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Old Jan 13, 2013, 10:38 PM
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Power supply for hotwire cutting

I know a lot of people are succesful at buiding a power supply unit with a transformer etc. I am however not to keen on trying to build such a device that will most likely be faulty on behalf of my electronics skills. I would like to know if anybody has used one of these types of power supplies to do the job. Any suggestions or thoughts.

http://www.mastechpowersupply.com/dc...a/prod_65.html

or

http://www.powersupplieswarehouse.co...wersupply.html

I also found this nichrome hotwire calculator to figure out the proper gauge wire and length of wire to stay within my parameters of the power supply.

http://www.jacobs-online.biz/nichrome/NichromeCalc.html
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Old Jan 14, 2013, 12:28 AM
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Battery charger

I don't know about the safety (so copy at your own risk) or the impact on my charger but I use the charger, which is a cheap 2-6-10 amp model. I used a "b" guitar string (.11 gauge) set the charger on 2 amps. It works well. Good luck.

Should clarify the charger is a trickle type car battery charger.
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Old Jan 14, 2013, 02:04 AM
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The first one is way too good for the application, but if the price is OK for you it will be an excellent PS for wire cutting.
Do Not use Nichrome . It's good for other applications but not for hot -wire-cutting foam.
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Old Jan 14, 2013, 02:37 AM
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I use a supply that I made since I do have the skill to do so, and it only cost me a few dollars because of that. But I was looking at a supply similar to what you've listed. They work great for bench power supplies but the thing that always held me back was that a lot of those units have a "short protection" that shut them down should they detect a "dead short", basicly when the positive and negative sides of the power touch each other, like when piece of wire is hooked up in a loop like what you would use for making a hot wire. You need a supply thats a bit more "dumb". Im not saying that the supplies you listed would not work, but it is possible they have that short protect circuit and be not really usefull for hotwire cutting.

here is another supply that I was looking at before I built mine:
http://www.mpja.com/0-18V-0-3-A-Vari...tinfo/9600+PS/

Most of my tools that I use range from 11watts (small hand tools) to 26watts (large 26" bow) of power. the table I use with about 5" of 22g steel wire uses 14watts. To figure out watts you take voltage and multiply it be the amps used. My table runs at 2v but pulls 7 amps. This is simply because of the way my power supply sends out the power. One of my older set ups would send out more volts, but less amps. Since my current set up uses 14 LM-317 variable voltage regulators, the way it is wired up it favors more amps for less volts. Watts is simply a unit of measure of electricity.

Sorry if Ive confused you more. Good luck with the hot wire cutting.
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Old Jan 14, 2013, 03:46 AM
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Outcast said: "... a lot of those units have a "short protection" that shut them down should they detect a "dead short", basicly when the positive and negative sides of the power touch each other, like when piece of wire is hooked up in a loop..."

Short protection is just what you want. It saves the unit from damage if it is overloaded by a short or other great demand.
A cutting wire is not a short circuit. It's the resistance of the wire that gives us the heat we so desire.
I use computer power supplies.
If the wire is too short the protection kicks in and keeps everything safe.
If the wire is just the right length I have a good hot wire cutter..
If the wire is too long it becomes a warm wire foam non cutter.
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Old Jan 14, 2013, 07:25 AM
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The first one is way too good for the application
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Old Jan 14, 2013, 07:47 PM
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Quote:
Originally Posted by Whiskers View Post
The first one is way too good for the application, but if the price is OK for you it will be an excellent PS for wire cutting.
Do Not use Nichrome . It's good for other applications but not for hot -wire-cutting foam.
I have two spools of braided picture framing wire. Used for hanging large artwork and medium sized artwork. Stainless steel wire. Would these work out for the hotwire? I also have some old guitar strings sitting around I can use. I know these will work. How does stainless steel heat up in comparisson to the nichrome. I would like to make a jig saw type hotwire with the hotwire only about 12" long coming out of a base to a jig.
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Old Jan 14, 2013, 08:15 PM
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Quote:
Originally Posted by Whiskers View Post
Short protection is just what you want. It saves the unit from damage if it is overloaded by a short or other great demand.
A cutting wire is not a short circuit. It's the resistance of the wire that gives us the heat we so desire.
I use computer power supplies.
If the wire is too short the protection kicks in and keeps everything safe.
If the wire is just the right length I have a good hot wire cutter..
If the wire is too long it becomes a warm wire foam non cutter.
Like I said, it was what held me back but Im glad someone has experiance with the more computerized systems and chimed in on that.
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Old Jan 14, 2013, 08:23 PM
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Originally Posted by OutcastZeroOne View Post
Like I said, it was what held me back but Im glad someone has experiance with the more computerized systems and chimed in on that.
Well if the wire is to short and the suplly kicks into protection mode and shuts down. Could you just reduce the amount of amps or volts and it would work or would it just keep shutting down meaning that you need to make the wire longer or use a larger gauge wire?
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Old Jan 14, 2013, 08:33 PM
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The SS will work far better than Nichrome which in optimized to work as a high temperature heating element that is under no tension loading.
It resists oxidation when red hot, but for foam cutting we're nowhere near red heat and the Nichrome's stretch and lack of strength is a pest.
If you buy that rather expensive but very nice PS you can easily get any SS wire to work.
Connect it up with the power turned way down and gradually come up until it is cutting the foam cleanly and without burning a wide kerf, A good cut usually has fine strands of thread on the cut surfaces. They are usually referred to as Angel Hair.
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Old Jan 14, 2013, 08:45 PM
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Thanks for all the help.
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Old Jan 14, 2013, 08:57 PM
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The SS picture wire can work very well. Just unwind one strand, put a it in a bow and carefully rub a dowel or screwdriver along it to take out the curl.

The power supplies listed should work. I think that the best wat to set them for hot wire cutting is to use the current adjustment. Start by setting the current limit high, adjust the voltage up until your are cutting too hot then adjust the heat down by turning the current limit down. Or... Just set the current limit below 1A, voltage high and slowly dial the current up until you get the right heat.

It is up to you to decide whether current or voltage limit works better. There are arguments both ways. In my personal experience current seems to work better.

J.P.
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Old Jan 15, 2013, 01:00 PM
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I want to know how I could utilize this power supply that I have sitting here. I used to use this for my old battery charging station. Would I be able to add some kind of dimmer dial to the output and use this for the hotwire?
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Old Jan 15, 2013, 02:02 PM
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If you have a charger that has a NiCd mode you can use that. A friend uses an old HiTec 325 charger to power his bow. I have used an Astro Flight 112. Set it for about 2A and dial it up or down from there as necessary to get the right heat. Most of our cutting has been done at about 2.5-3A when using .012 and .020 Stainless Steel wire.

J.P.
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Old Jan 15, 2013, 04:27 PM
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Originally Posted by VIDEOPRO View Post
I want to know how I could utilize this power supply that I have sitting here. I used to use this for my old battery charging station. Would I be able to add some kind of dimmer dial to the output and use this for the hotwire?
One way to do it is to make up some nice long leads to plug into those output sockets and terminate these leads with small alligator clips.
Then take a long piece of the cutting wire, say about 2 meters, and stretch it out fairly tight between some suitable supports.
Clip the leads on to the cutting wire spaced about as far apart as is convenient.
Apply the voltage and test the wire with a piece of scrap foam and move the clips closer together until the wire cuts the foam nicely.
Turn off the juice.
Now let's say the clips are now 1.2 M apart. This is now your *standard length*.
Make up your cutting tools so that the actual cutting wire and another piece of the same wire wound on a former slightly exceed the *standard length*
Hardwood can be used as a former and one of the clips is used to tap the wire and adjust the cutting temperature.
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