UPS to 12v Power Supply?

[jmartin]

Hi, (posted earlier to a different forum w/o obtaining specific recommendations)

I grabbed a 1000kva UPS (minus batteries) from work's bone pile, hoping I could turn it into a 12v power supply for my soon-to-be purchased battery charger. I find it begins putting out a little over 5 volts and then steps its way down to lower and lower (trickle?) voltages.

The charger I'm looking at (DuraTrax IntelliPeak ICE DC Competition Charger) says it needs 15 amps.

Have I got something I can fairly easily modify to do what I need? Or am I better off going back to the bone pile? For example, next week we'll be tossing out a large laser printer.

Thanks for any help and advice,

Jay

[Zeta Phoenix]

As I understand UPS's and how they work, they are a 12v battery connected to a inverter that kicks in when the power is removed from the input. So the voltages that you are seeing are likely the voltage to restore the battery to capacity after being drained (aka, you now have a nice 12v trickle charger). Look for any old PSU from PC's, with a jumper wire (ATX) or a switch (AT) they can be configured as a powersupply.

-Jon

[Rodney]

UPS converts 12 volts (a DC voltage) to 115 VAC, just the opposite of what you want.

[Miami Mike]

The large laser printer won't work either. :D

[Zeta Phoenix]

Again, look for an old computer power suply. There was another form here about modifing one as a 12v supply.

-Jon

[jmartin]

I think I'll try and grab a PSU off eBay. Thanks all,

Jay

[Fluke63]

I found a UPS in a parking lot and have taken it apart to see if it has potential as a power supply. I already have a PSU power supply for my chargers but the UPS transformer has the potential for more amps. I pulled two 12 volt 7ah baterries out of it already, so that's worth it in and of itself. The pc board has a rectifier built in to charge the batteries. So I powered the transformer directly and measured the DC output to the batteries. It's about 18volts w/ no load. It looks as if I could cut away most of the circuit board and just keep the rectifier part. I may be crazy but this is looking like a good possibility. Any input anyone??

[MatC]

jmartin: what are you actually trying to do? why not use an old 12v car battery? (cheap).

a UPS is a 12v battery charger and a 12 -> 240 (110 in US) volt inverter.

if you want 12v for your charger, either get a comp PSU (cheap and very good) or get a 12v car battery and charger, or get a 12v battery for your UPS and hang your charger in parallel with the battery. This may or may not work (eg the UPS may deem your battery charged at inopportune moments, integrate charge, measure voltage, etc). Also, the UPS battery is internal, so may not have much in the way of consumer mains isolation/protection, use at your own peril.

Fluke: perhaps, depends what the voltage under load is. Decent lead acid chargers float the battery at around 14v, 18v seems high. Bear in mind the above about internal circuits and such. What is your application?

[GlowFly]

IME computer UPS in kW size and up using internal batteries rarely use a 12v DC rail for reasons of efficiency. They often use multiple batteries in series to reduce the switching currents. My 1.5kW UPS for example uses 48v of internal lead acid batteries. Yours may use 2x12 = 24v. Even then if it's 1kW, 1000W/24v = ~40A for a few minutes.

Also, they rarely need to supply the ultimate in charging current to replenish the batteries. Usually it's better for them to err on the side of safety and aim for several hours at lower current.

I would suggest that the other recommendations of a converted computer PSU or discarded industrial 12v PSU would be a better choice.
--
Steve

[Acetronics]

Hi,

12v 15A ... that looks like a HAM radio supply ...

see there, there are tons at " Hong Kong" price.

12v15A aboard a computer supply ...??? CRAY 3 , may be !!!

Alain

[Fluke63]

To start out, I already have a converted computer power supply, but it only puts out about 7 amps. If I try to run 2 chargers pretty heavy it can't handle the load. I recently converted a more modern computer supply but it couldn't run any charger at all. The more recent the supply, the lower the amp output. So I figured let me play with this UPS that I found and see what the possibilities are.

The UPS transformer puts out 12V AC on the main taps when powered with 110v. The rectifier built into the circuit board has 4 aluminum plates with diodes and and I'm presuming voltage regulators. These could easily be sperated from the rest of the UPS control circuitry. And depending on where I measure voltage on the rectifier plates, I can get 5.99, 13.5 0r 19.8 volts DC.

By the way, this transformer has 4 wires going in, black, white yellow and blue. It has two tabs coming out. I thought the blue and yellow would be like a computer and be 12 and 5 volts, but that doesn't seem to be the case. Anyone know anything about transformers?

[Fluke63]

I'll add that the UPS transformer has to convert 110volts to 12volts while charging the batteries and then 12volts to 110volts while providing power during an outage. I'm guessing that's where the 4 wires come in, but I don't really know.

[MatC]

> 12v15A aboard a computer supply ...??? CRAY 3 , may be !!!

... or totally standard PC. http://www.power-on.com/at30atpow.html

[Fluke63]

Wow,
Every time I yank one out of a PC nowadays they're only 2-3 amps for 12volts. The one I have now is 7amps but it's an old one I got for $5.00 from a small PC shop and converted. If I needed one bad, I would buy that 15amp one. With this UPS I'm just tinkering around because it was free. If it doesn't work out, no big deal. Still got the 2 gel cells out of it.

[Lakc]

Just keep your eyes open, computer PSU's are generally free for the taking everywhere, although you often need to take a case and old motherbord with it :)
I am running an old PSU (no brand) and getting 15 amps on the 12v circuit. Im pretty sure a 250 watt PSU doesnt have all 250 watts available for the 12v circuit, but there are also 300-450 watt units out there as well.

[Fluke63]

OK, I'm not looking to beat a dead horse, but I'm relatively sure that all the parts of a good PS are here in the UPS. Transformer, rectifier, voltage regulator, etc. There's lots of discussions on other threads in the DIY forum where they're posting schematics and building PSUs. That's where I'm trying to go with this thread. Which is why jmartin started it in the first place. He just let it go when his need for a PSU was filled. But I really think this is worth exploring for the RC "Build it for little to no money" metallity that prevailed before the ARF generation took over.

On a side note, by looking thru the other threads in the DIY forum I discovered that the latest computer PSU I converted (which I mentioned above didn't work) actually does work. You have to connect the charger BEFORE you plug in the PSU. Then it doesn't trip off. It's only a 2amp unit, but it will certainly run the Triton charging a single battery. I hope that little tidbit helps someone else the way it helped me.

So I now have two working converted PSUs so it's not about that. But the guts in this UPS could deliver 15 amps at 13.5volts easy with not allot of work. Does anyone want to go on this journey? There's a hell of allot of UPSs out there and more and more are becoming available. They also have allot more juice available than your typical computer PSUs which are getting to be lower and lower current in general. So again I ask, anybody interested?????

[JRuggiero]

I converted a UPS to a general purpose power supply, and it works fine. Yes, you can put 110VAC (in the U.S.) into the high voltage side of the transformer and extract about 18VAC from the low voltage side. Then you can rectify it and add filter capacitors and voltage regulator. On my unit, the low voltage side of the transformer was center-tapped, so it needed only two diode rectifiers to convert AC to DC.

Under load, it can output about 15 amps at about 15 volts. I still need to work on a bettery voltage regulator.

If all you want to do is run a pack charger, a converted UPS is more trouble than it's worth. You are better off converting a computer power suppy for that purpose. If you are looking for a general purpose PS, converting a UPS is fun.

Jim R

[Fluke63]

Mr. Ruggerio,
Fun is what I'm looking for. Did you use the rectifiers and capacitors from the UPS, or did you supply different ones?

[vintage1]

All you need out of the UPS is teh mains transformer rectifier and big capacitor to smooth it. Chances are you can find those on Ebaty cheaper.

Regulating it down is a few butch power transistors and some smaller ones to drive em and a voltage reference - zener probably.

I was going that route but I got an EX CB PSU on ebay for less..

[jimimonet]

I think it is very simple, I use a UPS all of the time. I just opened it up and put a pair of bannana plugs on the battery. Now I have a fully charged 12 volt battery (really about 13.8 volts) to use with my charger. I just hook up my charger to the bannana plugs and it works fine and if I should need it I have a source of 110 volt AC as well in the field.

[MatC]

Lakc: indeed, most of the available power on older psu's is to the 5v rail, and 250W is of course the total. With more and more cpu/gpu/motherboards taking power from additional 12v connectors and converting it down to 1.3v or whatever they use these days, and increasing numbers of hard drives being used, the 12v line gets healthier by the year :)

[arx_n_sparx]

I know this takes the fun out of it, but..........

http://www.allelectronics.com/cgi-bin/item/PS-2157/480/DUAL_POWER_SUPPLY_--_2X_12_30A,_2.2_20A,_5_35A_.html

[JRuggiero]

Fun is what it's about. My UPS came from a thrift store. The battery was definitely shot, so I sent it to battery heaven. I used two other rectifiers from my stock, because I knew their ratings. Vintage1's comments on a few power transistors and such for output control are just what I tried. Got bored with the voltage drop, so for fun I'm now working on using power FETs. I used a computer-grade filter capacitor, also from my stock. Because the original case was an inconvenient size, I used the case from an antique -- and huge -- hard drive. Added two LED digital panel meters to monitor output voltage and current. A big handle from a screen door tops it off. Pics some other time.

Jim R

[Lakc]

On a side note, by looking thru the other threads in the DIY forum I discovered that the latest computer PSU I converted (which I mentioned above didn't work) actually does work. You have to connect the charger BEFORE you plug in the PSU. Then it doesn't trip off. It's only a 2amp unit, but it will certainly run the Triton charging a single battery. I hope that little tidbit helps someone else the way it helped me.

In my conversion it was mentioned that some sort of load must be put on the power supply or it will trip off. I believe I have a 10watt 10 ohm resistor across my 5v lines to keep it powered up.

MatC: Thanks for the feedback. Always good to know when your right or wrong.

[bravokilo]

JAY, WHAT YOU GOT IS PROBABLY A 1KVA UPS, NOT A 1000. CORRECT ME, BUT THAT LOOKS HUGE TO ME IF TRUE.

WHAT YOU CAN USE IS THE INVERTER TRANSFORMER TO MAKE A REGULATED POWER SUPPLY. AM SURE YOU CAN DOWNLOAD CIRCUITS IF YOU GO TO GOOGLE AND TYPE IN REGULATED POWER SUPPLY OR JUST SUPPLY. IF YOU HAVE A HAM NEARBY, HE SHOULD HAVE ACOPY OF THE ARRL HANDBOOK WHICH HAS PS CIRCUITS. THE INVERTER TRANSFORMER COULD BE A 12V TO 110 OR A 24 TO 110 IF YOU SAY YOU HAVE TWO BATTS IN THERE(OF 12V EACH i ASSUME). FORGET THE VOLTAGE YOU ARE GETTING WHEN IT IS PLUGGED IN, YOU ARE GETTING A TINY CURRENT TO CHARGE THOSE BATTS WHEN POWER IS ON. TO MAKE A 13.8V REGULATED POWEWR SUPPLY (OR 12V), YOU NEED A TRANSFORMER WHICH HAS AT LEAST 17 VOLTS AT THE SECONDARY. CHECK OUT IF THE TRANSFORMER IS ISOLATED BY TESTING CONTINUITY BETWENN THE TWO WINDINGS WITH A TESTER SET TO OHMS OF COURSE. FORGET ALL THE OTHER PARTS IN THE UPS. THE DIODES SHOULD BE OF THE RIGHT SIZE ANYWAY TO CONVER YOUR 17V SOMETHING TO DC. BTW, 24 WILL WORK, IT WILL JUST BE A LITTLE HOT ON THE BYPASS TRANSISTORS THAT YOU WILL NEED IN REGULATED PS. YOU NEED EXTRA COOLING.


BRAVOKILO