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Old Sep 17, 2012, 10:00 AM
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richie967's Avatar
Cardiff, UK
Joined Aug 2008
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Power Supply number 2

The original power supply build quality was pretty poor, so i have doubled my spend and got a new power supply...30v, 2.5amp Varibale

DC 0 - 30V (2.5A), fixed DC 5 and 12V (0.5A) outputs
Separate analogue voltmeter and ammeter
Current can be limited from 0 to 2.5A using the ‘current’ control.
Fixed outputs through ‘snap-on’ terminals and variable supply available at pair of terminal posts
Overload and short circuit protected

It is less amps than the other one, 2.5 as opposed to 15, however it has more volts, 30v compared to 15v.

It also has overload and short circuit protection built in, unlike the other one, so i am a bit more confident in trying it out without a garden! I'll still have the fire extinguisher close by though!

R
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Old Sep 17, 2012, 10:52 AM
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Joined May 2005
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that looks like a good little power supply. Have you tried it out yet? My concern with a lot of the prebuilt power supplies is that they have a "short cut off" built in and will shut down to protect the supply. Each one is different but if that one works, it looks like you got a very nice little bench set up.

When I built my last one I scratch built it useing 14 LM-317 adjustable power regulators for a total of 21 amps of power handeling ability. I also have used it to load test motors and other projects to see what kind of power they pull.

you can take a look at the thread I started for it here:
http://www.rcgroups.com/forums/showthread.php?t=1450332
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Old Sep 17, 2012, 08:31 PM
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vtdiy's Avatar
Southern Vermont
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Quote:
Originally Posted by richie967 View Post
The original power supply build quality was pretty poor, so i have doubled my spend and got a new power supply...30v, 2.5amp Varibale
It's got a relatively low amperage capacity, which means you will be restricted to very thin (.010 - .016") high resistance wire like stainless or nichrome.

I use .011" single strand stainless steel fishing leader wire.

Thicker wire, or materials like steel or carbon steel guitar string might not work with that PSU because of its limited current handling capability. Check with the hot wire calculator when choosing a wire for it.
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Old Sep 17, 2012, 09:28 PM
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Canada
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Wow! Seriously elaborate PS build there. Nice bit of craftsmanship though.
I've just used an Aircraft Spruce hot wire PS.
Basically a 24 volt Tx, a Ceiling Fan variable speed control and a xeroxed wiring diagram.. $18 back then :-)
Still works fine .. 20 years later.
Also use 0.08 SSteel from a set of ruined 1/2A control lines.. Proving to be a lifetime supply.. this stuff is Durable.
Have dabbled with a 'spare' Computer PS.. which works quite well, in case someone is after a v inexpensive and capable unit.
Lotsa ways to the same/similar result.
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Last edited by Bare; Sep 17, 2012 at 09:33 PM.
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Old Sep 18, 2012, 08:48 AM
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Southern Vermont
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Yup there is a huge variety of home built power supplies for wire cutting. From isolated (hopefully) variacs to transformers (or battery chargers) controlled by light dimmers, fan controllers, router speed controllers, as well as PWM circuits, computer power supplies with LED dimmers, or homemade air resistors. Then there is the Lipo, brushed ESC and servo tester (or even TX/RX) route. An automotive lead acid battery can also be used.

Richie started this thread because he wanted a purchased supply, rather than one he had to build. And that actually makes choices a little more difficult than any of the above.

He's been basically looking at bench type variable power supplies -- but with an eye toward reasonable cost. With the added requirement that they be readily available in the UK. Thus Harbor Freight router speed controllers coupled with a battery charger (my own weapon of choice) are out.

The hot wire calculator was written to determine a particular wire size and type for any PSU, given the voltage range and current capacity. And for any length bow, including short formed wire cutters. Thus it can help make a decision about what purchased power supply would be appropriate.
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Old Sep 20, 2012, 02:58 PM
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Cardiff, UK
Joined Aug 2008
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Power supply #2 has arrived!

Quote:
Originally Posted by vtdiy View Post
Yup there is a huge variety of home built power supplies for wire cutting. From isolated (hopefully) variacs to transformers (or battery chargers) controlled by light dimmers, fan controllers, router speed controllers, as well as PWM circuits, computer power supplies with LED dimmers, or homemade air resistors. Then there is the Lipo, brushed ESC and servo tester (or even TX/RX) route. An automotive lead acid battery can also be used.

Richie started this thread because he wanted a purchased supply, rather than one he had to build. And that actually makes choices a little more difficult than any of the above.

He's been basically looking at bench type variable power supplies -- but with an eye toward reasonable cost. With the added requirement that they be readily available in the UK. Thus Harbor Freight router speed controllers coupled with a battery charger (my own weapon of choice) are out.

The hot wire calculator was written to determine a particular wire size and type for any PSU, given the voltage range and current capacity. And for any length bow, including short formed wire cutters. Thus it can help make a decision about what purchased power supply would be appropriate.
Cheers, that's spot on! I would like to venture into the world of home built power supplies and light dimmer switches, it does sound interesting, When i have a garage/outdoor area to play in, i will certainly do that! I'm looking at best ways to ventilate the apartment whilst cutting, do you reckon a straightforward dust mask will do?

The power supply has arrived - it looks a lot better than the last one, about 3 times the weight, and built properly! will power it on tomorrow and hopefully get the Cathedral tail cut!
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Old Sep 20, 2012, 05:55 PM
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I'm looking at best ways to ventilate the apartment whilst cutting, do you reckon a straightforward dust mask will do?
No, it will not help in any way, styrene fumes are not dust. Maybe an organics cartridge respirator would work.

Mechanically, in cold weather, I guess you could ventilate fumes with some sort of blower and a couple of suction nozzles near either side of the blank, exhausting through a dryer hose outdoors.

Or maybe a big window fan exhausting outside behind the blank, in warm weather.

I cut my foam in an outdoor shed with 6 foot wide sliding doors open -- about 2 feet from the cutting table. Still I get plenty of fumes. Luckily I can leave during the cut, since my cutter is CNC!
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Old Sep 21, 2012, 07:30 AM
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Cardiff, UK
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Success!!!

Quote:
Originally Posted by vtdiy View Post
No, it will not help in any way, styrene fumes are not dust. Maybe an organics cartridge respirator would work.

Mechanically, in cold weather, I guess you could ventilate fumes with some sort of blower and a couple of suction nozzles near either side of the blank, exhausting through a dryer hose outdoors.

Or maybe a big window fan exhausting outside behind the blank, in warm weather.

I cut my foam in an outdoor shed with 6 foot wide sliding doors open -- about 2 feet from the cutting table. Still I get plenty of fumes. Luckily I can leave during the cut, since my cutter is CNC!
I have completed by first cut, it was supposed to be a test piece, just a small 200mm x 500mm Cathedral tail half, its turned out so well, There is a picture below, I am going to use these test initial cuts to learn how to fibreglass

Thanks all for all the input and comments, it has helped me achieve my goal, I am fairly happy that the Power supply and cutter are safe enough to use indoors.

I did it with Window open and fortunately the wind sucked the fumes out so i think it was okay,

i'll be in touch with another update shortly!!
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Old Sep 21, 2012, 09:19 AM
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That's a lot better looking than my first wing panel!
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Old Oct 10, 2012, 04:32 PM
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United States, MO, Fenton
Joined Jul 2012
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Novice trying to build a hot wire foam cutter

Hi, all,

I am planning to build a hot wire foam cutter. I have to confess that I am not very confidence with my understanding of electricity (besides turning on and off the light switch... ). After reading through and following the threads, I am still a bit confused as to how best to proceed.

I have a power supply that I use to run my LiPo battery charger (Thunder T610). It is printed on the power supply "12 volt, 20 amp". I know that this power supply outputs DC power. There is a LED screen on the power supply indicating the amperage. When I run my battery charger, the amperage would show a certain number and then starts to drop as battery charging is near completion. So, my understanding of this power supply is that it outputs a maximum of 12 volts, but the battery charger asks for a decreasing amount of voltage as time goes by, hence a drop in the amperage (V=IR, resistance is constant in this case).

So, I would like to be able to use this power supply as my power source for the foam cutter. I have not decided on the materials of the wire yet. I was thinking of using a guitar string as I have them lying around. Or, use carbon steel welding wires. The length of cutting wire probably less than 1 meter (3 feet). However I am concerned about electrocuting myself (with the 20 amp electricity). My questions are:

1) Is this power supply safe to use?

2) My understanding is that, without any voltage regulation, the power supply will put out 12 volts constantly. So, if I were to vary the length of the wire or distance between the two alligator clips (changing the resistance), I can get different amount of current going through the wire. Therefore, finding an optimal heat level. Is that correct?

3) If the power supply heats up the wire too much and, instead of changing the diameter or length of the wire (increasing R), I would like to regulate the voltage going into the wire, could I put a potentiometer in between the power supply and the cutting wire? If so, what kind of specs on the potentiometer should I be looking for?

Thanks for your input and suggestions!!
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Old Oct 10, 2012, 05:21 PM
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Southern Vermont
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Personally, I wouldn't use a Lipo charger for a cutting supply. There's often a lot of logic internally for providing a proper charge profile, and preventing overcharging or charging cells with too low voltage. etc.

Not saying it can't be done, but I wouldn't. A wire heating supply really can be a very simple power supply.

If you are in the US and don't want to wire anything, you can just get a 12 Volt 6 amp automotive battery charger and plug it into a Harbor Freight Router speed controller. Done. No wiring needed. And the speed controller has a built in fuse, 3 way switch and adjustment potentiometer, as well as a cord.

Not only that, you can also use both the charger and the speed controller for their original purposes as well -- just unplug them!

Be sure to use the hot wire calculator to determine what wire you can use for the length bow yo build.


EDIT: important -- you want the old style automotive battery charger -- the type with a meter on the front. There are some newer computerized chargers -- with LEDs for indicators -- these won't work. Computers screw it up for anything other than a battery charger (and the one I got is lousy at that as well!).

The old style (good) chargers always have a meter on the front.
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Old Oct 10, 2012, 06:02 PM
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Quote:
Originally Posted by vtdiy View Post
Personally, I wouldn't use a Lipo charger for a cutting supply.
Sorry to have mis-led you, vtdiy. The power supply I have is a separate unit from my LiPo charger. The power supply is supposed to put out 12 Volts and 20 Amps (somehow?). What I am confused about are the amount of voltage this power supply would put out and the amperage when I connect the cutting wire to the power. Also, I wonder if I need to regulate the voltage and/or amperage some how.


Quote:
Originally Posted by vtdiy View Post
If you are in the US and don't want to wire anything, you can just get a 12 Volt 6 amp automotive battery charger and plug it into a Harbor Freight Router speed controller. Done. No wiring needed. And the speed controller has a built in fuse, 3 way switch and adjustment potentiometer, as well as a cord.
Yes, I am in the US. I do own an automotive battery charger. It's a Black and Decker Smart Battery 10/6/2 Amp Battery Charger (http://www.sears.com/black-and-decke...SPM1055114501P). So, I would assume, from your post, that I could plug the Router speed controller into the wall socket and plug the battery charger into the Router speed controller to control the input AC power into the charger. Consequently, the DC output could be regulated. Am I correct on that? Should I set the output amperage to 6 Amp then?

By the same token, could I plug my other power supply (12 Volt 20 Amp) into the Router Speed Controller? Would the 20 Amp be an overkill or a buffer? I don't want to burn out that power supply or cause a fire somehow.

Thanks for educating me on this issue!!
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Old Oct 10, 2012, 06:05 PM
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Quote:
Originally Posted by vtdiy View Post
EDIT: important -- you want the old style automotive battery charger -- the type with a meter on the front. There are some newer computerized chargers -- with LEDs for indicators -- these won't work. Computers screw it up for anything other than a battery charger (and the one I got is lousy at that as well!).

The old style (good) chargers always have a meter on the front.
Just finished reading your post. I guess that my B&D automotive charger is one of the new kind. It won't work then...
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Old Oct 10, 2012, 06:10 PM
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Southern Vermont
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Nope that charger does not have a meter -- it has a digital display, and it's "Smart" which you don't want . You want Stupid!

You want a charger designed for humans to be smart about charging. These have a meter on the front (an ancient analog device with a needle that moves over a scale -- similar to the old device called a clock which had hands and a dial you could read.)

Here's an example of the old style charger:

http://www.harborfreight.com/automot...ger-45005.html
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Old Oct 10, 2012, 06:23 PM
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Southern Vermont
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Quote:
Originally Posted by f14tom View Post
Sorry to have mis-led you, vtdiy. The power supply I have is a separate unit from my LiPo charger. The power supply is supposed to put out 12 Volts and 20 Amps (somehow?). What I am confused about are the amount of voltage this power supply would put out and the amperage when I connect the cutting wire to the power. Also, I wonder if I need to regulate the voltage and/or amperage some how.
This one is probably a regulated DC supply so you can't use the router speed controllerwith it. The router speed controller works with ONLY with simple old fashioned unregulated transformer/rectifier type power supplies to provide DC, or a transformer alone to provide AC. (A hot wire can use either AC or DC since it is a simple heating element. Voltage should not exceed 24 V for most purposes. 12V is fine if you have enough current capacity (amps).)

If this is a regulated DC supply (check to make sure) you probably can use it if you put an adjustable DC regulator on the output. These are sold as LED lamp dimmers on Ebay. NOTE: that is NOT the same as an AC lamp dimmer switch.

Here's an example of a DC LED dimmer:

http://www.ebay.com/itm/New-12V-8A-L...-/180790381665

In this case you would wire the DC output of your power supply to the input of the DC LED dimmer. Then the output of the LED dimmer would go to the hot wire.

But you MUST be sure that your power supply is a DC 12 volt supply for the LED dimmer to work.
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Last edited by vtdiy; Oct 10, 2012 at 06:34 PM.
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