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Jan 05, 2010, 10:47 PM
ancora imparo
jj604's Avatar
Thread OP
Discussion

Using two power supplies for higher voltage/capacity chargers: safety issues


NOTE: Post 183 has my conclusions from the discussion in this thread.

In addition, we know a lot more about these supplies since this thread was started. For me it is now preferable to isolate the DC output ground on the second supply rather than isolate a ground on the AC side (which is what this thread is about). However this requires disassembling one of the power supplies and having accurate and correct information about what to do to modify it.

If you have the necessary skills and knowledge it is in my opinion the better way to go.

If you don't have that skill and knowledge you need to ask yourself whether you should be doing this. These supplies can kill you if you you don't know what you are doing.

I am recommending nothing - it is your decision if you want to tackle a dual series supply project or not.


With the growth of high capacity battery chargers there has been interest in beefier power supplies capable of managing two chargers simultaneously of up to 500Watts each. Commercial supplies of this capacity are expensive, particularly if you want 24V to get the maximum performance out of some of the new chargers like the Hyperions and others.

There have been a number of posts on modifying IBM, Compaq and HP server power supplies to provide 12V at 40-110A and this is pretty simple. A number of people such everydayflyer and feathermerchant have successfully combined two of these to provide 24V at high currents at moderate cost. These guys are experienced experts and know what they are doing but not everybody is, and there are some genuine risks in this approach.

I thought it would be helpful to start a thread where we could amass some reliable opinion to help the rest of us. If you are a lurking qualified electrician who really understands wiring practice please contribute!
NOTE: This is not the place for the “I made a $20 PC supply work by connecting the green wire….” stuff. There is plenty of info on that all over the net. This is specifically about connecting two high power server supplies in series to provide double the voltage.

To get started here is the problem, as I understand it – corrections and clarifications welcome.
The crude diagram attached shows how 12V two supplies are connected with their outputs in series to provide 24V.
The difficulty is that these supplies are all metal cased boxes with a common ground connection for the output and the 110 or 240V Mains ground wire. Under these conditions there is a connection ABCDEFG that is essentially a short across the output of Supply#2. The way round this is to break the loop at EF by disconnecting the ground pin on the #2 Mains plug. The following issues arise:

1.If the cases touch, then the short is re-established. Easy to fix by simple insulation or mechanical separation.

2.The manufacturer didn’t ground the case to protect the power supply, they did it to protect you. In the unlikely event a PS fails by a short from one of the mains inputs to the case then the resulting surge to ground will blow the fuse. If there is no ground, the surge goes through you if you are touching the case. This can be protected against by FULLY insulating Supply#2 but it’s not as easy as 1 above.

3.Even if Supply#2 is “untouchable”, it is connected to your charger by the –ve lead and if the charger case is connected to that, then the charger and possibly your LiPo can reach lethal mains voltage.

Welcome informed comments on how real the risk is and how it can be managed. For instance, is a fully insulated PS fed from an Earth Leakage Circuit Breaker acceptable practice?
Let the conversation begin.

SEE POST 183 for the final conclusions.

https://www.rcgroups.com/forums/show...&postcount=183

THE DIAGRAM BELOW IS NOT HOW TO DO IT
.


Also, as noted above, we now know a lot more about these server supplies than when this thread was started 3 years ago largely thanks to xandrios and other experts on the 12V 100Amp supply thread.

Most people would now float the DC ground on the 12-24V supply, not the AC ground if there is information available on how to do that. It is supply specific and some are already built with isolated outputs.

Here's how one guy did this for the supplies I have used in this thread.

https://www.rcgroups.com/forums/show...&postcount=678
Last edited by jj604; Feb 27, 2013 at 04:33 PM. Reason: Added reference to Post with the conclusions
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Jan 05, 2010, 11:25 PM
Use the 4S Luke
feathermerchant's Avatar
First off, thank you for starting this thread John.
My observations of the 3 points above -
1) If the cases touch, then one supply's 12V output is shorted and as these are high quality supplies, the shorted supply will just turn off its output. No big deal. MAybea spark and a burned spot on the case. I've seen it before...

2)Even though one supply is ungrounded, by virtue of the fact that its ground contact is connected to the other power supply's +12V output, the ungrounded shpply's case is at 12V above ground. Not a big deal under normal conditions. Forthe case to go above 12V, the grounded supply must somehow have a mains fault to it's 12V or I suppose the ungrounded supply could have a mains to case fault. Maybe we (I) should construcht a test to see what would happen.
I did plug in the ungrounded supply and measure the case potential before connecting its outouts to anything and the case stayed within a few tenths of a volt of 0 anyway.

3)Since the power supply output is grounded on one side, I doubt there's any danger to anything connected to it.

The greatest risk I see is that because I cut off the ground prong on one of the power cords, it could find its way to another application where a ground should be used. I have marked it on both ends with red tape to call attention to its unusual configuration.

I have observed that if I power up the supply first and plug chargers in second, thereis a loud snapas I connect the first charger and one power supply shuts down. I must first connect the chargers then plug in the AC power.

I have been using my unit at our flying field for several weeks now with no problems. All our outlets are run from ground fault circuit breakers. The breakers trip if current traveling out does not match current returning. ie current is 'leaking' to another return path other than the neutral wire in the circuit.

I have posted pics and details on my blog. I can post them here too if helpful.
Jan 05, 2010, 11:36 PM
Registered User
Himalaya's Avatar
That's what I did, with a minor mod for conveniency(one plug) and EMI consideration(shorter AC grounding path)



Note the inserted capacitor is just to make the grounding wire DC floating, all protection connections are still connected to ground like before, e.g. the two blue Y-capactors, the shielding case..etc.

This is what it looked like when finished. I got a high quality PS that's quiet(fanless), powerful(220x2=440W), and CHEAP.
Last edited by Himalaya; Jan 05, 2010 at 11:53 PM.
Jan 05, 2010, 11:42 PM
Registered User
I'm with Feathermerchant here. Before posting this last year I intentionally shorted the output of one of my 235's dozens of times to ensure that the protection circuitry was doing its job and adequately protecting the supply.

Obviously, running power supplies in series should only be attempted by those who understand and are willing to accept the risks involved. I emphatically agree that more discussion regarding mitigation of said risks is warranted given the number of high power chargers that are becoming commonplace and the resultant desire for affordable high current 24 volt DC. Thanks for starting this thread.

Mark
Jan 06, 2010, 12:39 AM
ancora imparo
jj604's Avatar
Thread OP
Thanks, for the quick responses everyone. Looks like we might get some good info all in the one place.

re:
Quote:
Originally Posted by feathermerchant
Forthe case to go above 12V, the grounded supply must somehow have a mains fault to it's 12V or I suppose the ungrounded supply could have a mains to case fault.
That is exactly the case that concerns me. That is where the UNGROUNDED PS has a mains to case fault. Would be relieved if someone could authoritatively show it would never be more than a 12V potential but I'm not convinced.

John
Jan 06, 2010, 04:31 AM
Registered User
BTW - the risk of mains voltage appearing on the case and/or the output terminals is very real. I had this happen to me on a switched-mode power supply about a year ago. This was an unmodified commercial supply which simply had an internal component failure. Luckily the insulation breakdown on the coil was only partial so there was still considerable impedance and I received only a minor shock rather than a fatal one. It did trip the earth-leakage breaker as well. Whether that would have been fast enough to save me had the breakdown been worse is hard to say. I am glad it was not put to the test!

As you might expect, I did not replace the PS with another one from that manufacturer.

Most of us are very complacent about electrical products primarily because of the high level of designed-in safety that is provided. My own view is that encouraging folk to bypass the safety features in order to save a few bucks is unwise and I recommend against both giving such advice and taking it. No matter how many caveats are provided, there will be folk who do not understand what they are doing that will try it out. The risk of bad outcomes is real.
Jan 06, 2010, 06:05 AM
Use the 4S Luke
feathermerchant's Avatar
kgfly - If the case was grounded, how did it have any voltage on it at all? Even if there in an internal failure, the case ground should prevent it from being dangerous.
Jan 06, 2010, 07:23 AM
Southern Pride
everydayflyer's Avatar
How to, why we should not or just this is what I think?

I have a 40 year old Black & Decker Drill Motor ( hand drill)with a metal housing and I cut the earth ground off of it approx 30 years ago . Why not I never connected the earth ground adapter to ground anyway.

When I was young 120 AC plugs were not polarized,they could be plugged in either way. They were two prong only. Appliances has metal housings. If a toaster and a coffee pot were both turned on and connected the right(wrong) way and you touched both you got a tingle. Unplug one of them and flip the plug ,problem solved.

Now we have polarized plugs, 3 prong plugs, plastic double insulated cases and we still need(?) ground fault circuits to protect us.

A 120VAC circuit has a hot (line) and has two grounds. One ground is called a neutral and the other is called a ground or an earth ground, both grounds connect to the same place that being Earth Ground.

Some bumass DIY type and even some so called electricians have been known to reverse the hot and netural connections at the wall socket. Now if you plug a 3 prong in to such a socket the earth ground (round pin) does a great service.


Received report that latest find are not the same as others. Whomever figures out power up be sure to post.

FYI I have ran two IBM 235s in parallel at 12+ volts up to just past 60amps. I have ran two of them in series at just over 24 volts and 800 watts output. At this point they were causing the overhead room light in my room to flicker a bit.

My series pair has served me well and is used daily.

https://www.rcgroups.com/forums/atta...7&d=1262697082

Charles
Last edited by everydayflyer; Jan 06, 2010 at 11:52 AM.
Jan 06, 2010, 07:30 AM
Registered User
Quote:
...the risk of mains voltage appearing on the case and/or the output terminals is very real..
The 240V was present on the output terminal, not the case. You are correct that if the internal fault had been to the case there would have been no risk since the breaker would blow whenever the unit was plugged in or turned on depending upon where the failure lay. My point was simply that these kinds of failures are not unheard of.
Jan 06, 2010, 07:49 AM
7000mw of raw power!
rich smith's Avatar
The same piggyback supply issues were brought up some time ago in this thread:

https://www.rcgroups.com/forums/show....php?t=1098857

Risk is real but in my case worth it and solved several power supply problems at almost no cost. Risk of getting hit by meteor or "green ice" is also real and everyone must decide for themselves.
Jan 06, 2010, 02:34 PM
G=667x10^-8 cm^-3 gm^-1 sec^-2
dissymmetry's Avatar
Personally, I keep a car battery on a car battery charger, all the time, I run everything dc off of that, and I have another battery and charger I can bridge to 24v, if I need that much, I have before. The batteries can be individually charged with their own 12v chargers, even while bridged in a series to 24v, without any issues. I know that my setup uses just a 2-10 amp charger, but the battery will make over 600 amps, so since I always keep the charger on it, I can get away with pulling 100 amps for at least an hour or two, without discharging the battery completely.
It works, and doesnt complain if the plug gets pulled, the battery will continue on, for a while, depending on the load.
Jan 06, 2010, 05:32 PM
Southern Pride
everydayflyer's Avatar
Why can a Thread never stay on subject here on RC Groups?

Charles
Jan 06, 2010, 05:43 PM
Registered User
Quote:
Originally Posted by everydayflyer
Why can a Thread never stay on subject here on RC Groups?

Charles
Perhaps you can tell us....

I'm still wondering what, if anything, the cost to ship a ten pound bag of sugar or potatoes to Australia has to do with the "HYPERION EOS NET, DUO, and DUO2 Chargers" thread.

https://www.rcgroups.com/forums/show...postcount=1931
Jan 06, 2010, 06:17 PM
Registered User
earlwb's Avatar
My question si why would someone want to ship a ten pound bag of potatoes or sugar to Austrailia. it can't be that expensive there. Maybe in Tokyo japan.


Anyway I think jj606 has the right approach to it. the problem is trying to keep the power supply cases apart at least the metal from touching. Plus covering the power supplies somehow to accidentally prevent yourself from touching them too. it doesn't happen often, but every now and then a failure can cause mains voltage to be on the case. usually the powersupply will shut down when that happens as it is grounded, but on the floating ungrounded power supply it needs to get protected somehow.

I like the other guy's idea on the capacitor across the cut ground connection too. it is a good thought.
Jan 06, 2010, 06:43 PM
ancora imparo
jj604's Avatar
Thread OP

Why I started this thread


I think I need to clarify something here since this is the kind of thinking I was hoping to avoid.

1) I NEVER "advocated" this approach. That's your decision. What I was trying to do was get some discussion from people who actually knew something about the subject. There is no shortage of opinion on the forums. It isn't always connected to fact. I happen to think, until someone authoritatively convinces me otherwise, that I won't take the risk. Other equally intelligent people will decide otherwise because in their informed opinion the risk is negligable. That's perfectly OK. What is important is that decision is based on facts.

2) "usually the powersupply will shut down when that happens as it is grounded, but on the floating ungrounded power supply it needs to get protected somehow" is EXACTLY what I don't care about. I am aware these are well designed machines that will normally look after themselves if they fail. There is a whole room of them in the floor below my office and they do that very well. But they are in professional racks in a professionally designed data centre. If we use them as Charger power supplies on the bench and disconnect a designed safety feature to do so then it is irrelevant if the PS can protect itself - it's protecting me that this thread was supposed to be about.

John
Quote:
Originally Posted by earlwb
Anyway I think jj606 has the right approach to it. the problem is trying to keep the power supply cases apart at least the metal from touching. Plus covering the power supplies somehow to accidentally prevent yourself from touching them too. it doesn't happen often, but every now and then a failure can cause mains voltage to be on the case. usually the powersupply will shut down when that happens as it is grounded, but on the floating ungrounded power supply it needs to get protected somehow.

I like the other guy's idea on the capacitor across the cut ground connection too. it is a good thought.
Jan 06, 2010, 08:27 PM
Tree Antagonist
BobOD's Avatar
Here's a problem I see that I'm not sure has been brought up. If something were placed across, or fell across, the two cases, there is a possability of conducting current (at 12v) and generating sparks and heat....maybe a fire. It could be a strand of wire, a carbon rod...who knows. This isn't very much different than a car battery sitting there but it's something to be aware of. Sometimes years later, people forget about the danger.

And, btw, gfi protection works by disconnecting the power if there is current flow detected in the ground prong of the recepticle. If you disconnect the case from this ground point, and the 3 - 400 volts dc typically found in switching power supplies shorts to this case, the GFI will NOT trip. It might with the capacitor (AC grounded) setup shown above....but it might not too.

BTW, 120v is childsplay as suggested above. DC is far more dangerous...has a better chance of stopping the heart.
Jan 06, 2010, 08:39 PM
Tree Antagonist
BobOD's Avatar
By the way, my suggestion, assumming no liability of course, is to get yourself a used PC case. Mount the 0-12v one grounded and the second (or third...) on insulated standoffs. Then everything is inside a grounded case.
Jan 06, 2010, 09:33 PM
ancora imparo
jj604's Avatar
Thread OP
My understanding is that the original gfi/ELCB's worked this way but that more modern ones work by detecting the imbalance between the Active and Neutral lines. If the current isn't the same in each it must be going somewhere else and they trip. Could be wrong about that though.

Some of us live where 240V AC is the norm and it seems to stop hearts pretty effectively. It's the current that kills you of course so it will depend greatly on the source impedance, how you are connected, the current path and your body resistance at the time but I always thought anything above 60V DC or AC needed to be treated as potentially fatal unless it was intrinsically current limited.
Quote:
Originally Posted by BobOD
And, btw, gfi protection works by disconnecting the power if there is current flow detected in the ground prong of the recepticle. If you disconnect the case from this ground point, and the 3 - 400 volts dc typically found in switching power supplies shorts to this case, the GFI will NOT trip. It might with the capacitor (AC grounded) setup shown above....but it might not too.

BTW, 120v is childsplay as suggested above. DC is far more dangerous...has a better chance of stopping the heart.
Jan 06, 2010, 09:37 PM
ancora imparo
jj604's Avatar
Thread OP
Interesting idea. What about my third point - the Charger case may be connected to the -ve lead and hence to the fault?
Quote:
Originally Posted by BobOD
By the way, my suggestion, assumming no liability of course, is to get yourself a used PC case. Mount the 0-12v one grounded and the second (or third...) on insulated standoffs. Then everything is inside a grounded case.
Jan 06, 2010, 10:30 PM
Tree Antagonist
BobOD's Avatar
Quote:
Originally Posted by jj604
Interesting idea. What about my third point - the Charger case may be connected to the -ve lead and hence to the fault?
Well, the -ve of of the ungrounded supply would not be accessible outside the case. The +ve of the ungrounded supply is but that is no different than than the original supply and is unavoidable. I don't design power supplies or anything but I would guess that they are designed such that the least likely failure to occur would be one that puts internal, high voltages on +ve. In other words, designed so if a failure in insulation were to occur, it'll go to -ve ground instead. Putting both inside a grounded case maintains the safety measures quite completely as best I can tell.

Regarding the GFI, a switching supply isolates input from output. There will be no imbalance for the gfi protection to sense while you cook. As far as it would be concerned, you would be the load.
Jan 07, 2010, 01:14 AM
ancora imparo
jj604's Avatar
Thread OP
Well, no to both of those I think.

1) The obvious failure that concerns me is if the Active (Line) Mains input connects to the ungrounded case. It happens. Possibly through a component failure or broken wire. In that situation the case is directly connected to the active Mains. But it is not grounded so the mains fuse will not blow. Any connection to the case which provides a path to ground (such as you) could be lethal. I would love to be convinced that it can't happen because of other current paths through the low voltage side but I'm not yet. My Hyperion Duo does not appear to have the case connected to either input or output but I wouldn't want to assume that for every charger. If the charger case is connected to -ve OUT from the supply, then it becomes live also.

2) "There will be no imbalance for the gfi protection to sense while you cook. As far as it would be concerned, you would be the load"

Well that's a trivial case and I agree that if you put yourself across the active and neutral then there is nothing that will protect you. But the failure mode we are protecting against is between active and ground. Then there IS an imbalance and that is exactly what ELCB type devices are designed to detect.

"a switching supply isolates input from output." So what? It's connection of the mains INPUT to case that is the danger.

This is turning out to be an interesting discussion. Thanks to everyone. Next opinion???

John

Quote:
Originally Posted by BobOD
Well, the -ve of of the ungrounded supply would not be accessible outside the case. The +ve of the ungrounded supply is but that is no different than than the original supply and is unavoidable. I don't design power supplies or anything but I would guess that they are designed such that the least likely failure to occur would be one that puts internal, high voltages on +ve. In other words, designed so if a failure in insulation were to occur, it'll go to -ve ground instead. Putting both inside a grounded case maintains the safety measures quite completely as best I can tell.

Regarding the GFI, a switching supply isolates input from output. There will be no imbalance for the gfi protection to sense while you cook. As far as it would be concerned, you would be the load.
Jan 07, 2010, 01:15 AM
Registered User
On some chargers the +ve is connected to the case, on others the -ve. Switched-mode PS isolate the input from the output to a degree, but if the insulation on the coil breaks down, a common failure mode, then the isolation can be violated.

I think Bob's suggestion of enclosing the pair of PS in a case which is itself grounded, such that only the main -ve and the main +ve are exposed, should bring you back to a safe setup so long as the floating PS is isolated from the case as Bob said.
Jan 07, 2010, 01:20 AM
ancora imparo
jj604's Avatar
Thread OP
This sounds like a key part of a safe solution - I agree. Whether it is enough I'm not yet convinced.

In mathematical proof terms it is necessary but is it sufficient?
Quote:
Originally Posted by kgfly
I think Bob's suggestion of enclosing the pair of PS in a case which is itself grounded, such that only the main -ve and the main +ve are exposed, should bring you back to a safe setup so long as the floating PS is isolated from the case as Bob said.
Jan 07, 2010, 02:10 AM
Registered User
When I had a quick look my first impression was an isolation transformer on the floating power supply might be benificial. Will have to think about this a little more. Something is not making me happy about what I again see posted. So far what it is it has not totally jelled. I think it has to do with a transformer in the floating supply becoming defective and going to ground. There is no longer a ground there so 120 volts is going to appear. The isolation transformer on the floating supply may reduce any risk of that occurance being dangerous. Again I will have to think about this. All I think is the event of that likelyhood is small but must be protected from. A ground fault device may be able to be wired into the floating unit instead.
Last edited by barry wilson; Jan 07, 2010 at 02:23 AM.
Jan 07, 2010, 03:20 AM
Registered User
Stupid idea of the day:
How about a zener diode/SCR crowbar between ungrounded supply and ground, set at 15-20 volts or so? In normal use it would be off and isolation between supplies is maintained, but when high voltage leaks into ungrounded case, the crowbar is triggered into conduction, creating a short and tripping the elcb. Of course it would also short the output of the supply and possibly take damage itself, but that would be only collateral damage necessary to protect the more important pieces of the system (aka. you).
Jan 07, 2010, 11:14 AM
Tree Antagonist
BobOD's Avatar
Quote:
Originally Posted by jj604
If the charger case is connected to -ve OUT from the supply, then it becomes live also.
No, not really. If the -ve of the charger is connected to its case and to the -ve of the first grounded power supply, then the charger case is grounded and will not be live.


Quote:
Originally Posted by jj604

2) "There will be no imbalance for the gfi protection to sense while you cook. As far as it would be concerned, you would be the load"

Well that's a trivial case and I agree that if you put yourself across the active and neutral then there is nothing that will protect you. But the failure mode we are protecting against is between active and ground. Then there IS an imbalance and that is exactly what ELCB type devices are designed to detect.
You are assuming that the ground source for any particular situation is the GFI protected one. There are other ground sources...the ground is one of them and it is not GFI protected.


Quote:
Originally Posted by jj604
"a switching supply isolates input from output." So what? It's connection of the mains INPUT to case that is the danger.
No it's not...well, it's not the only danger anyway...nor even the major concern. Switching power supplies often generate high voltage DC as a first step. They do this as a way to regulate high power without having to deal with such high current. I have one here that runs a 375vDC buss and stores a good amount of this energy BTW. This is so much more dangerous than even 220vAC.It is clearly designed to send any faults into the ground circuit. The grounded case is the most relied upon safety barrier. Eliminating it avoids this safety measure.

Putting both inside a grounded case, in my mind...not an expert by any means...maintains this safety measure quite well. Probably not perfect but a whole lot better than removing a primary safety measure and leaving it exposed. Even forgetting about an internal failure, I go back to my first mention. You have, by design, a large metal case at 12v with a lot of current capacity. It may not electrocute you but it is a fire hazard. For someone who is conscious of it, probably be OK as long as we pay attention all the time.
Jan 07, 2010, 11:18 AM
Tree Antagonist
BobOD's Avatar
Quote:
Originally Posted by kgfly
On some chargers the +ve is connected to the case,
I really wish they would not do that.

Do they still make pos grounded autos these days. That's probably what that's all about.
Jan 07, 2010, 12:34 PM
Adam
xStatiCa's Avatar
Quote:
Originally Posted by BobOD
You have, by design, a large metal case at 12v with a lot of current capacity. It may not electrocute you but it is a fire hazard. For someone who is conscious of it, probably be OK as long as we pay attention all the time.
I am confused by this. I am no electronics expert but I do remember from electronics class many moons ago that current is the killer not voltage. I have heard 1 amp can be lethel but on the other hand extremely hight voltage at very low amperage(a few millivolts for example) would not. Vandergraf generator experiments with hair standing on your head is a good example. Can you clarify what you mean?
Jan 07, 2010, 01:08 PM
7000mw of raw power!
rich smith's Avatar
Current is the killer but it requires voltage to get through the skin. Static is high voltage (i.e. half million) but harmless because low current. 12 high current DC (car battery) is pretty harmless too because not enough voltage to penetrate. 110/220vac is the most dangerous and accounts for most electrocutions because it has both.

Note that you can never be hurt unless the potential is across your chest like one hand to the other or head to foot. Getting hit finger to elbow or finger to palm is painful but can never electrocute.
Jan 07, 2010, 01:44 PM
Tree Antagonist
BobOD's Avatar
Quote:
Originally Posted by xStatiCa
I am confused by this. I am no electronics expert but I do remember from electronics class many moons ago that current is the killer not voltage. I have heard 1 amp can be lethel but on the other hand extremely hight voltage at very low amperage(a few millivolts for example) would not. Vandergraf generator experiments with hair standing on your head is a good example. Can you clarify what you mean?
I never understood the notion that "current is what kills". Power is what does the damage and power is a funcion of voltage AND current.

Anyway,
Your body is a resistor and has a rather high resistance.
Current (I) = Voltage (v) / Resistance (Ohms)

If the voltage is only 12v, then the current will be 12 / 200000 ohms (just to pick a number) = 0.06 milliamps. Not enough to harm.
At 300v, it's 300 / 200000 = 1.5 milliamps. Enough to do harm.
Jan 07, 2010, 02:07 PM
Registered User
earlwb's Avatar
The problem is if the skin barrier is breached then the internal body resistance goes way down.
Usually it takes about 100 ma of current to maybe stop the heart.

1 mA Barely perceptible
16 mA Maximum current an average man can grasp and "let go"
20 mA Paralysis of respiratory muscles
100 mA Ventricular fibrillation threshold
2 Amps Cardiac standstill and internal organ damage
15/20 Amps Common fuse or breaker opens circuit

ref: http://www.cdc.gov/niosh/docs/98-131/overview.html
Jan 07, 2010, 02:44 PM
Adam
xStatiCa's Avatar
Thanks for the info everyone. Very informative.

According to that article...

dry skin 100,000 ohms
wet or broken/wet skin 1,000 ohms
skin under high voltage(not really defined) could be reduced to 500 ohms

So some simple math shows...

Broken skin:
20v source with broken skin(1000ohm) at 20mA can cause respiratory paralysis.
12v source is safe which would only give 12mA

Dry skin:
2000v source with dry skin(100000ohm) at 20mA can cause respiratory paralysis.

I am sure you can not depend on these numbers but they are probably somewhere in the ballpark if that article is correct.

I also read somewhere that the vandergraph generators that people use to make their hair stand up generally produce around 27 microamps which is way below even 1 milliamp so that is why they are safe with high voltage(millions of volts).

I got that from the excerpt below from that url.

"The presence of moisture from environmental conditions such as standing water, wet clothing, high humidity, or perspiration increases the possibility of a low-voltage electrocution. The level of current passing through the human body is directly related to the resistance of its path through the body. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms. The following illustrations of Ohm's law demonstrates how moisture affects low-voltage electrocutions. Under dry conditions, Current=Volts/Ohms = 120/100,000 = 1 mA, a barely perceptible level of current. Under wet conditions, Current=Volts/Ohms = 120/1,000 = 120 mA, sufficient current to cause ventricular fibrillation. Wet conditions are common during low-voltage electrocutions.

High-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms. Once the skin is punctured, the lowered resistance results in massive current flow, measured in Amps. Again, Ohm's law is used to demonstrate the action. For example, at 1,000 volts, Current=Volts/Ohms = 1000/500 = 2 Amps, which can cause cardiac standstill and serious damage to internal organs. "
Last edited by xStatiCa; Jan 07, 2010 at 02:52 PM.
Jan 07, 2010, 04:07 PM
ancora imparo
jj604's Avatar
Thread OP

A plea from the OP


Folks this is proving very informative. Thanks to everyone. I need to think about the comments BobOD has made, particularly about a failure in the primary DC side - excellent point.

Can I ask that we don't go off on a "Effect of electricity on the human body" path. I sense it coming.

There is plenty of info on that elsewhere. For this thread I wanted to look at the design requirements for safety. Let's just agree these little boxes are dangerous if a high voltage gets out and figure out how to gauard against that.

Thanks, John
Jan 07, 2010, 05:45 PM
Use the 4S Luke
feathermerchant's Avatar
Oh JJ and I work for the electric Co.

Does anyone think we (I) should conduct a test to see what would happen if one of these 24V "supplies" were to suffer a mains to case fault on the ungrounded power supply?
Jan 07, 2010, 05:51 PM
Registered User
earlwb's Avatar
Quote:
Originally Posted by feathermerchant
Oh JJ and I work for the electric Co.

Does anyone think we (I) should conduct a test to see what would happen if one of these 24V "supplies" were to suffer a mains to case fault on the ungrounded power supply?

I would not ask someone to do it. But if you have your heart set on it. Do video record it for posterity. You could blow out a power supply doing the test. Maybe even the components would let out all their stored up smoke too.

jj604,
I would fabricate some sheet plastic boxes and covers to minimize the chance of accidentally touching both cases at the same time. Here in our Home Depot or Lowes big box hardware stores, they sell assorted types of acrylic plastics in varying thicknesses that one can buy. Then one can slice it up and glue together or something to make some covers. The covers do not need to completely encase the power supplies. If you had both supplies next to each other, you could just make a U shape affair to put over the top and leave the ends open. heck if one can heat the plastic up, they could bend it over like one does for sheet metal. That way if you happened to accidentally lean over or put a hand on them, you wouldn't actually touch the metal cases. You would have to be deliberate and remove the cover, so at that point you would be more careful.
Last edited by earlwb; Jan 07, 2010 at 05:56 PM.
Jan 07, 2010, 05:52 PM
Registered User
No better way to find the truth than experimenting. If it isn't too much trouble, I would appreciate a well documented test. Of course only if, as a professional, you feel confident that you can do it safely.
Jan 07, 2010, 06:44 PM
Southern Pride
everydayflyer's Avatar
Two 3235s under glass, Plexieglass that is. They have been happy with their home for months.

https://www.rcgroups.com/forums/atta...7&d=1262697082

Charles
Jan 07, 2010, 07:16 PM
Team SCHC
zguy's Avatar
From this document:

http://www.meanwell.com/images/print%20pdf/faq.pdf

4. If we need a 24V output power supply, but MEANWELL does not have this model, can we use two
12V power supplies connecting in series instead of one 24V power supply?
Ans: YES, basically you can do this to get the right output voltage, but be careful that the rated output current of the series
system should be the rating of the minimum one in these series connected power supplies. Furthermore, we like you
to parallel a diode at the output of power supply to prevent possible damage of internal capacitors.

5. If we need a 600W output, can we use two units of S-320 connected in parallel?
Ans: No, you can not do this connection because S-320 is not equipped with the parallel function. When two power supplies
are connected in parallel, the one with higher output voltage will share more loading and deliver more (even “all”)
power to the load and cause these two power supplies to be unbalanced. We suggest using PSP-300 or PSP-500
because it is equipped with the current sharing function.
Jan 07, 2010, 07:43 PM
ancora imparo
jj604's Avatar
Thread OP
Thanks for that. Anybody know about the diode for series use?

Re the quote below. The particular server supplies I use are "hot swappable" and are designed to run in parallel and load share. HOWEVER I don't know whether the smarts are entirely inside each PS and/or rely on signals to the staus/control pins. Everydayflyer, feathermerchant and others have used server supplies in parallel I'm pretty sure and have measured load sharing currents. Charles can you put in your experience here please?

John
Quote:
Originally Posted by zguy
From this document:

http://www.meanwell.com/images/print%20pdf/faq.pdf



5. If we need a 600W output, can we use two units of S-320 connected in parallel?
Ans: No, you can not do this connection because S-320 is not equipped with the parallel function. When two power supplies
are connected in parallel, the one with higher output voltage will share more loading and deliver more (even “all”)
power to the load and cause these two power supplies to be unbalanced. We suggest using PSP-300 or PSP-500
because it is equipped with the current sharing function.
Jan 07, 2010, 08:25 PM
Southern Pride
everydayflyer's Avatar
From over a year ago

IBM 235 Server Power Supplies in parallel

--------------------------------------------------------------------------------

Notice !! Not responsible for sparks and such. Proceed with caution. The power supply you kill may be your own.


These IBM 235 Server Power Supplies seem to have some rather sophisticated power management built into them.
As stated in post above 15 amps. is the max. current load they will start under and then amps. can be increased up to 30 without any problem and they hold 12 volts+.

Note: The problem I experienced with more than a 15A starting load was due to the type of load( bulbs) not the power supplies. They will handle a 30A load at startup or atleast as fast as a charger can ramp up.

Well I decided to connect two in parallel and do a little load testing.



If they are started with no load then a 30 amp load can be connected after they have booted up,no problem. Now here is the interesting part. Only one is carrying the load and the other is just there. One can be powered down and the other wil carry the full 30 amps.. Next power the other one back up and start to increase the load. At just over 32 amps. the second one starts to share the load. At 45 amps they are each supplying approx. 1/2 of the total.

Not sure who would need a 45 amps. plus PS but it can be done.At 45 amps. I noticed the volatge starting to drop just below 12 volts and as I could not see any point in pushing them anymore I stopped the test.
================================================== ===

I have sense ran they at just over a combined 60 amps. and I have ran them in series at just ove 12V and just over 30 amps. for 800 watts output.

The IBM 235 are just about bullet proof. I have done all kinds of destructive testing, shorting outputs,shorting cases together while connected in series with one earth ground removed , powering up and shuting down one at a time,running only one for hours on end with other one not powered up. Worse outcome has been one or both shutting down requiring them to be powered down and back up.

The Diodes . I have used a full wave bridge on a switching ps output to protect it from reverse current from a battery in case of a power outage, It Is also a good idea to perhaps place diodes from neg. to pos. on power supplies operated in series in case one loses power blowes a fuse or happens to be on a seperate AC line that drops outs . Same could be applied to ones in parallel.


A bit OT but not really.

http://www.school-for-champions.com/.../ac_wiring.htm

An explanation with drawing of why IMO we now have polarized and 3 prong AC wiring..
Charles
Last edited by everydayflyer; Jan 07, 2010 at 08:46 PM.
Jan 07, 2010, 08:59 PM
ancora imparo
jj604's Avatar
Thread OP
Thanks, Charles that's useful. Also the link to what is a nice straightforward summary of supply conventions.

For folks who live in different countries, the US explanation is still valid with the exception that some places don't allow 2 pin at all TBofMK (eg the UK and HK where plugs are also independently fused) and other places use angled plugs for the two supply connections to ensure a more obvious orientation on two pin varieties (eg Aus and NZ). Also the voltages may be 220-240/415 rather than 110/220 although in 240V countries virtually all domestic use is 220-240V single phase. Wire colours will be different as well. Old here used to be Red and Black where US has Black and White and we had Green or bare for the 3rd pin. Modern is Brown (Active) and Blue (Neutral) with Striped Green/Yellow for the 3rd pin. Accomodates for colour blind electricians.

One thing that may be important in this discussion is the supply capacity. Two of the HP supplies I am using would rate at 1820Watts for a 110V supply or 2600Watts on 240V. That's about 17Amps US and 11Amps in Australia. My 40 year old house has 16Amp fuses/circuit breakers on the power circuits.

Have one of these double supplies running on the same circuit as the TV and your wife turns on the iron or clothes drier and everything goes off. I would regard this as as safety issue of a different kind if she happens to be watching a particularly important program at the time.

John
Quote:
Originally Posted by everydayflyer

http://www.school-for-champions.com/.../ac_wiring.htm

An explanation with drawing of why IMO we now have polarized and 3 prong AC wiring..
Charles
Jan 08, 2010, 03:56 AM
Registered User
Himalaya's Avatar
Quote:
Originally Posted by BobOD
Here's a problem I see that I'm not sure has been brought up. If something were placed across, or fell across, the two cases, there is a possability of conducting current (at 12v) and generating sparks and heat....maybe a fire. It could be a strand of wire, a carbon rod...who knows. This isn't very much different than a car battery sitting there but it's something to be aware of. Sometimes years later, people forget about the danger.

And, btw, gfi protection works by disconnecting the power if there is current flow detected in the ground prong of the recepticle. If you disconnect the case from this ground point, and the 3 - 400 volts dc typically found in switching power supplies shorts to this case, the GFI will NOT trip. It might with the capacitor (AC grounded) setup shown above....but it might not too.

BTW, 120v is childsplay as suggested above. DC is far more dangerous...has a better chance of stopping the heart.

That is why I modified jj604's diagram to mine, as shown in post #3. All casing/shieldiing/filtering/protecting connections that were originally connected to Mains ground are mantained connected to ground. The only mod to do is to make the negative output DC floating.
Jan 08, 2010, 07:37 AM
Southern Pride
everydayflyer's Avatar
Himalaya your post will not be grasped by many who read it. It is extremely difficult at times to get a point across here on these Forums.

Turns out we and not really talking about removing a ground any way.







Snip:

Quote:
MORE ABOUT "GROUNDING" AND "EARTH"
In electrical circuits, the word "ground" can be very confusing. The word has several different meanings. Your instructor might know which meaning he or she is using in any spoken sentence. But this spreads confusion, because students aren't even aware of the multiple meanings. Or even when students know that "ground" is a multi-facted term, they may lack skill in connecting each definition. It's better to ban use of the word "ground" in the classroom. That forces everyone to use less confusing words.


The word "ground" means:

A 'common' connection, but not connected to Earth.
A connection to the power supply (usually to the negative terminal)
A connection to the inside of a shielded metal box
A connection to a metal stake driven into the earth (or a connection to a metal water pipe which extends out of the house into dirt.)
Only number four is actually connected to ground!
For those with a curious mind.

http://amasci.com/amateur/whygnd.html

Snip:
Quote:
Another thing: sometimes an appliance with a metal case will suffer internal wear or damage, and then the "hot" wire will wiggle around inside and end up touching the metal case. Anyone standing on wet ground will feel pain and death if they should grab that metal case.


Some unnamed genius realizes that if we could somehow permanently connect all the metal cases of appliances to the "neutral" wire, then if the "hot" wire should ever accidentally touch the case, a short circuit would blow the fuses in the building and quickly remove the electrical connections, and the hazard. However, this is not entirely safe. Occasionally an electrician will accidentally wire an outlet backwards. This can't be helped, because Perfect Electricians are far more expensive than the normal human variety. And so we cannot intentionally wire appliance cases to the Wide Prong of the plug, since it would cause a lethal hazard if the appliance was plugged into a miswired wall outlet. Miswired outlets look exactly the same as the normal ones.


The solution? Why, add a Third Prong! Connect this prong to the neutral side of the network, but do it only in one place in the circuit, and run a new third wire out to all of the wall-outlets. Give this wire a new color, one which is different from the other two. Give this this third prong a very different shape as well, so even Highly Imperfect Electricians will rarely connect the special prong to the wrong wire. Inside metal-cased appliances, insist that manufacturers connect this third wire to the case.


The idea works! Like magic the faulty metal-cased appliances start blowing their fuses to indicate trouble. And power tools dropped into water will create a current path to the metal case rather than to nearby humans standing in the puddle. We've entered the "Age of Electrical Outlets Having a Little Face and Different Sized Eyes."


Charles
Last edited by everydayflyer; Jan 08, 2010 at 09:21 AM.
Jan 08, 2010, 11:35 AM
Tree Antagonist
BobOD's Avatar
Quote:
Originally Posted by Himalaya
That is why I modified jj604's diagram to mine, as shown in post #3. All casing/shieldiing/filtering/protecting connections that were originally connected to Mains ground are mantained connected to ground. The only mod to do is to make the negative output DC floating.
That may work for power supplies with isolated outputs but some have the - terminal grounded internally. A supply with isolated outputs should have a separate earth connection and it is up to you to properly earth any connected devices. These supplies could have their cases (assuming they are metal cased) grounded no problem. It's the non-isolated supplies depicted in the drawings of post 1 and 3 that present the problems.

And BTW, your capacitor is a good idea for shorting AC mains leakage but it doesn't block a HV DC potential...the more dangerous one.
Jan 09, 2010, 05:39 AM
Which way is it going now
mstone's Avatar
Why not just stick a 16VDC MOV between the cases then and high voltage will be shorted to ground if a fault does occur.

I haven't seen the insides of the cases but is it not possible to isolate the outputs from the case so the cases can touch?

Cheers
Mark
Jan 09, 2010, 07:28 AM
Southern Pride
everydayflyer's Avatar
Quote:
I haven't seen the insides of the cases but is it not possible to isolate the outputs from the case so the cases can touch?
Another computer with the can not view the first post of a thread syndrome.

Charles
Jan 09, 2010, 08:52 AM
Registered User
earlwb's Avatar
Quote:
Originally Posted by mstone
Why not just stick a 16VDC MOV between the cases then and high voltage will be shorted to ground if a fault does occur.

I haven't seen the insides of the cases but is it not possible to isolate the outputs from the case so the cases can touch?

Cheers
Mark
Generally on these types of power supplies most all if not all of the circuit board mounting screws are grounded to the case. It helps to prevent RFI.
You may or may not be able to redo the mounts to isolate the circuit boards.
Plus on many of these power supplies the heat sinks for the power transistors can actually be part of the case sides too.
Jan 09, 2010, 09:08 AM
Southern Pride
everydayflyer's Avatar
Can we first agree that PS # 1 is still safe as it is un modified?

If so then PS # 2 is the issue. Simplest solution IMO is to house it so that it is insulated and is reasoning behind my Plexiglas shield as posted in the past.

Now if some feel that is not enough it could be fully enclosed with only the power leads going in and coming out.

If that is still not enough then the Hot 110-120 AC line could be fused and in fact I believe if one checks they are indeed already fused. Now I realize that fuses are slow to blow and may not prevent electrical shock so what if a 110 V AC coil relay is added as shown. According to my logic the relay would only be powered up and thus close the open ground circuit if the case somehow goes hot with 110 AC going to it. An even simpler Warning Only solution would be a 110 V panel indicator light wired same as the relay coil.

I guess this still leaves the possibility of DC in some form making its' way to the case. This brings us back to encasing the power supply or coming up with a means to sense both AC and / or DC on the case and shorting it to ground.

I am not an EE but I have been shocked a few times.

If this post is really off base then I will gladly delete it.


Update to below update: The two I checked are as follows, two others have posted same experience with their's however there are conflicting reports as well. Perhaps these are not all the same.

Update This is a significnate ,please read carefuly.
If you are using these very same power supplies as singles then nothing has charged however if you are using them in series ...

I have done more testing and determined that in fact the DC grounds are in fact isolated from the AC (case/earth)ground. What does this mean. In simple terms it means that the can be used in series with the earth ground connected to both units and it also means that the cases do not have to be isolated from each other(tey can touch) and it also means that with the earth ground connected they are now much safer to use.

Very same being hp Series ESP 114
Part # 192147-001

Charles
Last edited by everydayflyer; Jan 20, 2010 at 05:22 PM.
Jan 09, 2010, 10:01 AM
Which way is it going now
mstone's Avatar
I did read the first post. It didn't say why the case could not be disconnected from the output.

Anyway, a MOV will protect you from a fault. Will limit the case voltage to say 16VDC, above ground, which should give the fuse and/or RCD a chance to blow before killing any one.

In most cases with power supplies the FG is all about passing EMI/EMC tests.
Jan 09, 2010, 10:24 AM
Use the 4S Luke
feathermerchant's Avatar
I have looked inside a few supplies. In one, not only were the circuit board mounting screws grounded but that socket where you plug in the mains cord is actually an EMI/RF filter. The outside is metallic and grounded and there is even a schematic on it showing how the various components are connected. It has a ground pin that is wired to the case but even if you remove that, the metallic outside of the socket is grounded and mounted to the metal case makes the case grounded anyway.
In several supplies I have seen there is a fuse in the 'hot' (120V) input which, if blown, would remove any hazard from thepower supply. I think the MOV might be a good idea because it could clamp the voltage and give the fuse time to blow. MOV's are also much faster than a relay.
Jan 09, 2010, 03:18 PM
Southern Pride
everydayflyer's Avatar
Everything I read about MOVs seems to imply that they need to be used with a properly connected ground. I guess I do not understand how they would function in this application.

Best site I found

http://www.answers.com/topic/varistor

I am also confused on how in the world we ever survived all those years with next to no protection against electrical shock . I mean non polarized 110 plugs,incorrectly wired sockets, metal housed appliances and tools yet somehow most were never electrocuted to death.



Charles
Last edited by everydayflyer; Jan 09, 2010 at 03:46 PM.
Jan 09, 2010, 03:47 PM
Registered User
earlwb's Avatar
I don't beleive it is all that bad. Just go ahead and setup one power supply to float and shield them so you don't accidentally touch both power supplies at the same time. You are only trying to prevent yourself from doing something stupid when the brain housing group isn't working right at the moment.

Important tip, don't stand in water when you are messing with the power supplies plugged in to the mains.


If a power supply fails or has a problem, it'll shut down, more or less automatically. These server supplies have a lot of smarts built into them already.
Jan 09, 2010, 03:56 PM
7000mw of raw power!
rich smith's Avatar
Duct tape does a great job of insulating the upper supply as mentioned in my original thread. Even before the supply was insulated they were shorted several times, both by accident and on purpose. The only thing that happend was they had to be powered down and up again. Fuse never even blew.
Jan 09, 2010, 04:34 PM
Registered User
Even if you have protected the human involved when an accident occurs what is going to happen to the charger plugged into the supply? Based on the fact we are talking 500w chargers as stated in the original post you aren't exactly talking about a throw away charger. If I were setting up a charging system as being discussed here I would be very sure that any sort of fault wouldn't trash the charger. If that chance was there I'd go to an electrical surplus place or ebay and find an HP 1000W supply. They appear to be going for around 500-800 dollars at this time.
Jan 09, 2010, 04:43 PM
Southern Pride
everydayflyer's Avatar
Perhaps read post # 6 again

The only way to insure that a charger is never exposed to any danger from a power source is to use only batteries as a power source.


Charles
Jan 09, 2010, 05:00 PM
ancora imparo
jj604's Avatar
Thread OP
Just to make it clear:

"I don't beleive it is all that bad. Just go ahead and setup one power supply to float and shield them so you don't accidentally touch both power supplies at the same time. You are only trying to prevent yourself from doing something stupid when the brain housing group isn't working right at the moment. If a power supply fails or has a problem, it'll shut down, more or less automatically. These server supplies have a lot of smarts built into them already."

"Duct tape does a great job of insulating the upper supply as mentioned in my original thread. Even before the supply was insulated they were shorted several times, both by accident and on purpose. The only thing that happend was they had to be powered down and up again. Fuse never even blew. "

For this thread, I wasn't really interested in protection of the PS while it is working as designed. I have always assumed the design of these things is such that they will protect themselves against most abnormal conditions and that is clearly the case. In practice we have found that they just shut themselves down if they are overloaded or unhappy in any way.

"I am also confused on how in the world we ever survived all those years with next to no protection against electrical shock . I mean non polarized 110 plugs,incorrectly wired sockets, metal housed appliances and tools yet somehow most were never electrocuted to death."

Fair enough Charles and I totally agree. I actually have come to the conclusion that simply insulating the second supply case from the first and putting a big label on it saying "Ungrounded Case - Do not touch while switched on" is probably reasonably adequate for the folks who are in discussion here. It's the old psychological solution. I am not in favour of modifying a professionally designed high power device by adding components when we don't have a schematic or clear understanding of how they are designed in detail. Adding a case/wrapping that isolates the second supply and ensuring that the supply which still has a mains grounding pin is the one connected to the output -ve is what I will probably do myself as a reasonable balance of protection and hassle.

Like you, I think the risk is very very small of one of these things failing in a dangerous way - but it can happen. We had over 50 power supplies literally blow up in a data centre some years ago due to an environmental contaminant no one could reasonably have predicted before the fact. (According to the guys that were there at the time it was quite exciting!)

However, the reason I started this was the concern that there are people out there who will happily stick two of these supplies together if they see advice that it can be done and who haven't the faintest clue how electricity works or what the dangers are, particularly because it is "only 12Volts". That was what prompted my original comment way back in the 12V 100A supply thread about this technique. Of course it works and of course it is perfectly reasonable and safe if you know what you are doing. A brief peruse of some of the wacky actions on YouTube will remind us that ignorance of consequences leads people to do some really dumb things - the point is they don't necessarily know they are dumb.

It just seemed to me that if we could pull in the good minds on this topic we might end up with some fairly simple accepted views for anyone who wants to try it. Bit like LiPos. In the early days when people didn't understand how they were different from NiCds and everybody had DeltaV chargers, then sharing what we knew got us to where we are today - a quite reliable fantastic mass produced energy source that although it is being used outside "normal" practice is by and large perfectly safe.

And no, I don't want to start another feral track on the pros and cons of LiPo safety please.

John

PS: By "normal" practice above I meant that sticking an uncased LiPO in a fragile toy aeroplane and sending it dashing round the sky in a sometimes controlled manner with the real possibility of abrupt termination from a great height while drawing continuous currents at the limit of the battery capacity is probably not "normal".
Last edited by jj604; Jan 09, 2010 at 05:12 PM.
Jan 09, 2010, 06:18 PM
Registered User
earlwb's Avatar
Yeah you are correct. The big worry is someone reading that we have done it, and then they go out and try it without understanding what it is they are doing.

Please people, if you read this, use extreme caution, it can be very dangerous.
Jan 09, 2010, 07:58 PM
ancora imparo
jj604's Avatar
Thread OP
UPDATE Apologies: I didn't read the post properly. You are of course correct in referring to the charger cost. I think the risk to the charger however is negligable. The chances of getting a higher than designed voltage on the charger that would blow it seem very small to me.

Well earlwb has discovered a nice one that will provide 55A @ 12V and 45A @ 3.3V so two of these would give you a 12, 15.3, 24V supply at 45/55A. Total cost $20 plus shipping. Sounds just about throw away to me in the very unlikely event anything happened to one of them.

Also the supply that I converted that started this thread IS a 1000Watt HP supply. Actually 900/1300 depending on supply voltage. See picture of the label in

https://www.rcgroups.com/forums/show...5&postcount=91

Cost about $30 each depending where you get it from.

Quote:
Originally Posted by linkless
Even if you have protected the human involved when an accident occurs what is going to happen to the charger plugged into the supply? Based on the fact we are talking 500w chargers as stated in the original post you aren't exactly talking about a throw away charger. If I were setting up a charging system as being discussed here I would be very sure that any sort of fault wouldn't trash the charger. If that chance was there I'd go to an electrical surplus place or ebay and find an HP 1000W supply. They appear to be going for around 500-800 dollars at this time.
Last edited by jj604; Jan 09, 2010 at 09:54 PM.
Jan 09, 2010, 08:56 PM
Registered User
i have 4 of the 40 amp from feathermechanic and am looking into combining them.
A 2p2s setup would be nice but i am getting ahead of myself.
Current i have a simple queation ; while here people have used tape to insulate the case i think its a messy solution and am looking for the shrink tube like used for battery packs to insulate them (and avoid them to scratch ect) so does anyone have source for the right size stuff i am looking for?
Jan 09, 2010, 09:02 PM
Registered User
I would be very suprised if you can heatshrink the PS as it is likely to be covered with vents for cooling air flow.
Jan 09, 2010, 09:05 PM
Registered User

front rear only


the ones i have have only vents at the rear and front so using tube insulating will not cover that

Quote:
Originally Posted by kgfly
I would be very suprised if you can heatshrink the PS as it is likely to be covered with vents for cooling air flow.
Jan 09, 2010, 09:16 PM
Registered User

how one of mine looks now


i use 4mm "banana" connectors as standard so i also aded them to this one.
While measuring the epoxy board i forgot that the metal of the case did not reach all the way down.

on the other 3 i have it does but i did not yet install the connectors since i only use one so far anyway
Jan 09, 2010, 09:44 PM
Registered User
earlwb's Avatar
Quote:
Originally Posted by linkless
Even if you have protected the human involved when an accident occurs what is going to happen to the charger plugged into the supply? Based on the fact we are talking 500w chargers as stated in the original post you aren't exactly talking about a throw away charger.
Well actually the power supplies that everydayflyer and myself are using are 800w max (660w max on 12v) and they cost$10.00 each, refurbished. So yeah we could probably blow up a few and still not be too upset about it.

Actually my inexpensive chargers could be considered throwaways. $46 each. The Hobby King Quattro charger costs $99, but has 4 chargers built into it. But yes my iCharger models are more expensive though not exactly throwaway items.
Last edited by earlwb; Jan 09, 2010 at 09:52 PM.
Jan 09, 2010, 09:47 PM
Registered User
earm linkless refers to the charger not the cost of the psu
Jan 09, 2010, 09:50 PM
Registered User
earlwb's Avatar
Quote:
Originally Posted by cmulder
i have 4 of the 40 amp from feathermechanic and am looking into combining them.
A 2p2s setup would be nice but i am getting ahead of myself.
Current i have a simple queation ; while here people have used tape to insulate the case i think its a messy solution and am looking for the shrink tube like used for battery packs to insulate them (and avoid them to scratch ect) so does anyone have source for the right size stuff i am looking for?
I don't like duct tape as it leaves a yucky sticky gummy residue that is difficult to remove. Plexiglass or acrylic plastic sheet from our local Home Depot or Lowes hardware superstores would work well. Heck plywood would likely work well too as long as you don't get it wet.
Now heat shrink tubing is a interesting thought. But I do not remember ever seeing it that large in size though. So I'll have to check out what they have at our local Altek Electronics store next week. I work near the store.
yes one leaves the ends open if you have a powersupply that blows or pulls air through the ends and out through the ends.
Jan 09, 2010, 09:54 PM
Registered User
Here in Ireland we don't have those huge stores like home depot or lowes..
Was in the states last year and have spend a hour or 2 wandering around in a lowes store.
If only overweight luggage was not so expensive........
Jan 09, 2010, 09:55 PM
ancora imparo
jj604's Avatar
Thread OP

Aplogies


Thanks, you are absolutely right. I have updated my original reply.

Quote:
Originally Posted by cmulder
earm linkless refers to the charger not the cost of the psu
Jan 09, 2010, 10:06 PM
Use the 4S Luke
feathermerchant's Avatar
Quote:
Originally Posted by cmulder
Here in Ireland we don't have those huge stores like home depot or lowes..
Was in the states last year and have spend a hour or 2 wandering around in a lowes store.
If only overweight luggage was not so expensive........
Hey -Try emailing TanicPacks. Brian is real nice and as he builds hs own battery packs, he probably has the right size shrink lying around.
If he won't ship, I can get it from him and ship. It should fit in a USPS small flat rate box. I'd gusee $25 or so for shipping.
Jan 09, 2010, 10:33 PM
kit
kit
Registered User
Heat shrink film

http://www.mcmaster.com/#shrink-wrap/=5b2xl9
Jan 10, 2010, 03:07 AM
Electric Helis is my game
MrMel's Avatar
Sidenote, but what are the aspects of running powersupplies in parallel?
I have 2 x 40A, 1 x 60A 15v powersupplies, problem is that I cant use them fully unless I can connect them in parallel.

Can it be done (at least for the 2 x 40)?
Last edited by MrMel; Jan 10, 2010 at 03:47 AM.
Jan 10, 2010, 04:30 AM
ancora imparo
jj604's Avatar
Thread OP
Hot swappable server supplies are designed for this. Charles did quite a bit of work with his IBMs. See Post #40 below.
Quote:
Originally Posted by MrMel
Sidenote, but what are the aspects of running powersupplies in parallel?
I have 2 x 40A, 1 x 60A 15v powersupplies, problem is that I cant use them fully unless I can connect them in parallel.

Can it be done (at least for the 2 x 40)?
Jan 10, 2010, 04:40 AM
Electric Helis is my game
MrMel's Avatar
What about those that are not designed for it(or unknown at least), can it be done?
Jan 10, 2010, 06:21 AM
ancora imparo
jj604's Avatar
Thread OP
Anyone out there tried two dissimilar/non hot-swap supplies in parallel? My guess is you might run into problems where the voltage out wasn't exactly the same if the regulation kept trying to hold a target and the second supply was doing the same but for a different target voltage. Unlike batteries in parallel, the PS regulation is expressly designed to actively work to keep the output reaching a "natural" common level. Just speculation though - I don't know.
Quote:
Originally Posted by MrMel
What about those that are not designed for it(or unknown at least), can it be done?
Jan 10, 2010, 06:27 AM
Registered User
If they are not specifically designed for parallel/load-sharing operation then it is very unwise to attempt it. I believe the most likely outcome is blowing one of them.
Jan 10, 2010, 07:23 AM
Southern Pride
everydayflyer's Avatar
Once again as to insulating the case(s) see one of my earlier poast in this thread with link to mine. According to my calculations it would take approx. 25 oz. of Plastic coat / Dip It or Liquid tape to put a 10 mil (0.010") coating on one of these hp power supplies.

http://www.plastidip.com/diy.php

I think my Plexiglas looks cool.

https://www.rcgroups.com/forums/atta...7&d=1262697082


and reposted here for those with linkless computers.


Charles
Last edited by everydayflyer; Apr 04, 2010 at 12:30 PM.
Jan 10, 2010, 08:02 AM
Registered User
earlwb's Avatar
In my opinion they look pretty good.
Could you go over your method of bending the plexiglass over for the one piece U shaped cover?
Jan 10, 2010, 08:23 AM
Southern Pride
everydayflyer's Avatar
Plexiglas can be formed when heated.Measure ,cut, clamp (between straight edges) heat,apply pressure, watch it bend. I clamp between 2X4s using C clamps and heat with a Towers Mono Coat Gun which I have had for close to 30 years.

Like many things best to practice with scrap pieces at first. I have fabricated similar guards , shields for many machines, assembly fixtures, etc. I designed / built during my working career.



Charles
Jan 10, 2010, 09:48 AM
Tree Antagonist
BobOD's Avatar
I've bent plexiglas in an oven. Make a mold which could be as simple as a block of wood. Put the plexi on top of the mold and put into a 250 degree F oven. Watch it bend over the edges of the mold (about 10 minutes). For smaller pieces, I've even used a toaster oven.
You'd be surprised how easy it is to work with.
Last edited by BobOD; Jan 10, 2010 at 02:48 PM.
Jan 10, 2010, 10:41 AM
7000mw of raw power!
rich smith's Avatar
You are both confusing Plexiglass with Lexan. Plexiglass (acrylic) will burn before bending while Lexan (polycarbonate) will bend. The difference is important.
Jan 10, 2010, 10:54 AM
Southern Pride
everydayflyer's Avatar
What ever you say professor. I have yet to see any plastics that can not be formed after heating.

The Plexiglas I use comes from Home Depot ,Lowe's ,Ace Hardware etc. and is sold as a replacement for window panes where breakage is an issue.

http://www.diynetwork.com/decorating...ets/index.html

The issue here perhaps is spelling similar but different. I concede there may be a registered trade name with very specific spelling that perhaps is a form of plastic that tends to burn before being able to softened enough with heat to be form but I am unaware of such.

When most request a Kleenex they will be satisfied for the most part with any decent grade tissue.



Charles
Last edited by everydayflyer; Jan 10, 2010 at 11:15 AM.
Jan 10, 2010, 12:43 PM
7000mw of raw power!
rich smith's Avatar
Quote:
Originally Posted by everydayflyer
What ever you say professor. I have yet to see any plastics that can not be formed after heating.

The Plexiglas I use comes from Home Depot
I'm not sure what planet your shopping on but I'm positive the half dozen around here do not carry Plexiglass but a cheap imitation of Lexan called "crystal" something. Being a polycarbonate it can be bent with heat but acrylic cannot.

The people in your link are just as confused as you which is probably true of 99% everybody else too. Like you say the "kleenex" syndrome. But the difference is critical not just semantics.

http://www.professionalplastics.com/...YLICSHEET-CAST

Key word "CAST".

I suggest as an after class exercise you research acrylic/polycarbonate.
Jan 10, 2010, 12:54 PM
Electric Helis is my game
MrMel's Avatar
Searching "bend acrylic" comes up with lots of videos & tips how to do it, all using heat?
(even "plexiglass with a copyright sign")
Jan 10, 2010, 12:59 PM
Southern Pride
everydayflyer's Avatar
As I posted above

Quote:
I have yet to see any plastics that can not be formed after heating.
Charles
Jan 10, 2010, 01:05 PM
7000mw of raw power!
rich smith's Avatar
Quote:
Originally Posted by MrMel
Searching "bend acrylic" comes up with lots of videos & tips how to do it, all using heat?
(even "plexiglass with a copyright sign")
I'm guessing they are all making the same mistake, thinking they are working with acrylic when actually it's polycarbonate. All I can say is personal experience shows me otherwise. Attempts at heat bending resulted in microcracks and anything more than couple degrees it just snapped.

Higher temperatures only result in disintegration and fire.

We will have to agree to disagree on this subject. Nothing pleases me more than being the only one in the room with a clue.
Jan 10, 2010, 02:31 PM
Registered User
Quote:
Originally Posted by everydayflyer
As I posted above

Charles
We saw your post the first time.

Just because a plastic may be be able to be formed by heating doesn't mean there aren't some types of plastics that work better than others for the task at hand.

Acrylic vs Polycarbonate
Jan 10, 2010, 02:40 PM
Electric Helis is my game
MrMel's Avatar
Quote:
I'm guessing they are all making the same mistake, thinking they are working with acrylic when actually it's polycarbonate. All I can say is personal experience shows me otherwise. Attempts at heat bending resulted in microcracks and anything more than couple degrees it just snapped.

Higher temperatures only result in disintegration and fire.

We will have to agree to disagree on this subject. Nothing pleases me more than being the only one in the room with a clue.
Think its more like PeteB says, different type is better for the job at hand.
You can bend all with heat, some is harder and require better tools like PMMA (Acrylic)
(There is special machines built for it)
Jan 10, 2010, 02:55 PM
Tree Antagonist
BobOD's Avatar
Well, for the record, I was talking about acrylic (plexiglass).
If I had been talking about polycarbonate, I would have suggested a higher temperature (325 degrees F plus) as it has a higher glass transition temperature than acrylic.

I'm not sure which material is easier to work with but I have bent plexiglas in a toaster oven many times with good results.
Jan 10, 2010, 03:13 PM
Southern Pride
everydayflyer's Avatar
Using link Pete provided above


Quote:
Dec 17, 2009 ... Even with high grade acrylic and polycarbonate the trend continues. ... Home depot usually stocks acrylic but polycarbonate can be scarce ...
www.overclockers.com/forums/showthread.php?t... - 21 hours ago - Cached
So which one was I most likely to have purchased from Home Depot?

Charles
Jan 10, 2010, 03:58 PM
Registered User
My local Home Depot has a ton of plexiglass/acrylic in all sorts of sizes/thicknesses. They do stock some polycarb but it's ridiculously expensive compared to acrylic sheet.

Like Charles, I've had no issue forming plexiglass to my heart's content with no cracking or breaking issues.

Mark
Jan 11, 2010, 01:58 AM
Registered User
Himalaya's Avatar
Quote:
Originally Posted by BobOD
That may work for power supplies with isolated outputs but some have the - terminal grounded internally. A supply with isolated outputs should have a separate earth connection and it is up to you to properly earth any connected devices. These supplies could have their cases (assuming they are metal cased) grounded no problem. It's the non-isolated supplies depicted in the drawings of post 1 and 3 that present the problems.

And BTW, your capacitor is a good idea for shorting AC mains leakage but it doesn't block a HV DC potential...the more dangerous one.

All switching PSUs(AC adaptors) are isolated inside using transformers with strictly insulated primary and secondary windings instead of a single coil. They CAN appear as a non-isolated one if the manufacturer wants it to be. Mine are like this. Open it up, find the wire that connects neg. output to mains ground, cut it and insert a capacitor to make it DC-floating, and you're done.

As for the DC potential, please note that the PS#1's neg.output is grounded, so the DC potential appears across the added cap is only 12V.

Finally I realized opening the case up may look threatenning to many. Looks like the guys here are talking about serializing two PSUs without internal mod. I didn't post in a right thread and I am sorry for that.
Jan 11, 2010, 11:18 AM
Tree Antagonist
BobOD's Avatar
Quote:
Originally Posted by Himalaya
All switching PSUs(AC adaptors) are isolated inside using transformers with strictly insulated primary and secondary windings instead of a single coil. They CAN appear as a non-isolated one if the manufacturer wants it to be. Mine are like this. Open it up, find the wire that connects neg. output to mains ground, cut it and insert a capacitor to make it DC-floating, and you're done.

As for the DC potential, please note that the PS#1's neg.output is grounded, so the DC potential appears across the added cap is only 12V.

Finally I realized opening the case up may look threatenning to many. Looks like the guys here are talking about serializing two PSUs without internal mod. I didn't post in a right thread and I am sorry for that.
Yes, this is a great way to do it. Then both cases remain connected to earth ground. In fact, at that point, I would just attach both cases together with some metal straps. The only issue is that disconnecting these internal connections can be a bit of an effort depending on the design of the power supply.

For those that don't want to work internal to the supply, the same can be achieved by mounting both supplies inside another metal case, one PS case grounded and one on insulators without the earth wire on the input. Then put this capacitor between the floating case and the outer case. This results in the same thing. PS#2 will have its neg line grounded for AC and the exposed case will be earth grounded for AC and DC.

Adding the capacitor is a good point, thanks.
Jan 11, 2010, 11:24 AM
Registered User
what i guess is that in the psu i use (see pics) they use a mounting point of the board to also act as ground connection to the metal case so removing that would mean grinding away one of the board supports.
Btw since the case is the issue has anyone already taken the boards out of the case and just combined 2 inside a new case?
that would be the nicest looking solution and relative save.
Jan 11, 2010, 02:19 PM
Adam
xStatiCa's Avatar
Quote:
Originally Posted by Himalaya
All switching PSUs(AC adaptors) are isolated inside using transformers with strictly insulated primary and secondary windings instead of a single coil. They CAN appear as a non-isolated one if the manufacturer wants it to be. Mine are like this. Open it up, find the wire that connects neg. output to mains ground, cut it and insert a capacitor to make it DC-floating, and you're done.
There is very little chance of me attempting anything like this because I am happy with just 12v but I am curious. What do you mean with the capacitor. Are you saying cut the wire, put a capacitor in line with the wire you cut and then connect it up again or leave the wire unconnected? If you just cut the wire and put a capacitor on the end of the wire without connecting it up again would the cap charge without being connected on one end? You have be doubting my limited understanding of electrical circuits.
Jan 11, 2010, 04:57 PM
ancora imparo
jj604's Avatar
Thread OP
If you look at the picture of the internals of the HP "100A" supply I posted at

https://www.rcgroups.com/forums/show...9&postcount=28

You will see that these are a tightly integrated mechanical unit. You could take the board out of the case but it's going to be a bit of work to put them in a new case with proper cooling paths etc. Starting to look like a major project I think.

John

Quote:
Originally Posted by cmulder
Btw since the case is the issue has anyone already taken the boards out of the case and just combined 2 inside a new case?
that would be the nicest looking solution and relative save.
Jan 17, 2010, 02:09 PM
Southern Pride
everydayflyer's Avatar
http://www.doityourself.com/stry/qnawiring7

Snip:
Quote:
Q. My receptacle tester (yellow with three prongs) indicates open ground on my GFCI outlet. The reset button on the GFCI works. Please tell me if open ground means the GFCI is not working. In addition, part of the house has been updated with new wiring and circuit breakers, but the older wiring doesn't have a ground wire. At least one of the GFCI's with the open ground does have a ground wire to the receptacle. Maybe it is not connected at the breaker or fuse box?

A. GFCI receptacle will work just fine without a ground wire, so having an open ground on the receptacle will not reduce the shock protection. Be leery of using computers or other electronics on this ungrounded circuit, however. GFCI will protect people from shock, but will not protect equipment from lightning/ spike damage even with a surge protector.

It's quite possible that the ground wire is not connected at the panel box if your original wiring was not grounded. The inspector may want you to replace the GFCI receptacles because newer GFCI's have better technology that makes them more reliable. I doubt he can enforce this unless there is a code article giving him that right, however.

With an ungrounded GFCI, it's okay if pushing the "TEST" button on the face of the GFCI causes the receptacle to lose power, then the GFCI is working properly. No other test is reliable, especially the GFCI test button on any external tester. It is amazing to me how many inspectors don't realize that just because their external tester won't trip an ungrounded GFCI, it does not mean that the GFCI is not working properly.
So if I understand this it would seem that a GFCI on the ungrounded( no earth ground) power supplies would be a fairly simple safe solution and in fact it would appear that neither case would need the earth ground,

Any professional electricians out there care to weight in?

Charles
Last edited by everydayflyer; Jan 17, 2010 at 02:14 PM.
Jan 17, 2010, 02:26 PM
Registered User
http://en.wikipedia.org/wiki/Residual-current_device
Jan 17, 2010, 05:01 PM
Registered User
don;t those devices only "trip" when there is current "missing" ?
For the current to be "missing" it has to return to earth trough another path for example the body of a person tutching a live wire (or case).
So the person will still experience a (shorter ect) shock.

Not a problem for me personally but others might dislike it
Jan 17, 2010, 05:10 PM
Southern Pride
everydayflyer's Avatar
My point all along has been if you do not touch the ungrounded supply it can not shock you. Others say but what if. I suggested (asked why not) the GFCI device for the just in case group. Yes you could still get zapped a bit but it would not be leathal.

Charles
Jan 17, 2010, 05:59 PM
Registered User
Good thing is that here mains voltage is 220 instead of the whimpy 110 volts you guys have overthere (who came up with that anyway ; higer currents / more losses in cabeling ect)
So anyone who tutches live here ussaly gets verry motivated not to try that one again.
Jan 17, 2010, 10:38 PM
ancora imparo
jj604's Avatar
Thread OP

Here we go


Oops, wrong answer. Stand back folks - Charles the field is yours.

Me, I'm a 240V person but neutral on this. As far as I can tell the quality of the electrons is identical; except of course that down-under ours run in the other direction through the circuits.

Quote:
Originally Posted by cmulder
Good thing is that here mains voltage is 220 instead of the whimpy 110 volts you guys have overthere (who came up with that anyway ; higer currents / more losses in cabeling ect)
So anyone who tutches live here ussaly gets verry motivated not to try that one again.


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