Cheap power supply for hot wire cutter - RC Groups
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Jan 15, 2003, 09:26 PM
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ferradas's Avatar

Cheap power supply for hot wire cutter

Just thought I'd pass along the info. I built a power supply for my wire cutter using Joedy Druilas plans

I don't know much about electricity and wiring but these plans were pretty straight forward.

It works great! The foam cuts nicely around 3-4 volts, it goes up to 8 volts ( using the dimmer switch ).

Cost was about $25.00 to build but you can reduce the cost by not using the voltmeter and using cheaper wood than what I got at the hobby shop.

So if anyone is looking to make one of these, I highly reccomend this one.

Now I'll focus on the vacuum pump
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Jan 15, 2003, 09:28 PM
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ferradas's Avatar
Oh yeah, all the components were bought at Radio Shack except for the dimmer switch ( Home Depot ), and I added the banana plug connectors that werent on the inventory list.
Jan 30, 2003, 04:42 PM
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I have a few questions about this power supply. First off it appears to me that the out put of this unit will be AC current. According to the specs on the transformer this would be either 13VAC or 26VAC depending on how you wire it. Is this amount current dangerous and which way should it be wired
Jan 31, 2003, 01:53 AM
Whadda YOU lookin' at?
CactusJackSlade's Avatar

It's DC

Ulrich Dick,

I built a unit just like "ferradas" above using the info at charles river.

It does indeed output DC voltage. I have only tested mine on a few blocks of foam and it works quite well.

Seems to cut good at about 4 volts or so on the meter.

I am no electrician and had to re-do the wiring on the voltage meter a couple times... had to ask ferradas for help. If I get around to it I will post a modified wire diagram a baby can understand (that would be me).

I also made a bow using an extension cord, PVC electrical pipe, a few bits of hardware and ss fishing line.

Here is what I built:
Jan 31, 2003, 01:57 AM
Whadda YOU lookin' at?
CactusJackSlade's Avatar

Hot wire cutter

Oh, I used a 110v socket inside the box to plug the bow into and the holes in the box are for ventilation... the transformer gets pretty hot. I chose a plastic electrical box because it was easy to work with and pre-made.

I think I have about $70 in everything, maybe less...

Here is another view....
Jan 31, 2003, 12:27 PM
Silent Majority
Bert's Avatar
Could you explain how you connected the meter up (which is also not in the parts list at Charles River).

Jan 31, 2003, 09:43 PM
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Those of us lucky enough to have one of the Astroflight digital chargers already have a power supply for cutting foam. I had heard about this before I got my FeatherCut and it's powersupply, but I had to try it! My Astro 110D works every bit as well as the unit that ships with the FeatherCut.

To do this you have to hold the red button down when powering up. This puts the chargers in a test mode that changes the display to show source voltage and turns off the peak detection.

Have fun,

Feb 01, 2003, 12:49 AM
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ferradas's Avatar
here's what it should look like... the diode is an IN4001 found at radio shack and the resistor comes with the voltmeter.
Feb 01, 2003, 04:03 AM
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OK, now I'm confused!
On the transformer it states output of 12.6 VAC. If I use my voltmeter, it also shows an AC output of aprox 12.6VAC across one output and the ground, or aprox 26VAC across the two yellow outputs. I am not an electritian either, just a little confused. Maybe you can wire in the DC voltmeter using the diode and use it on AC current. Anyway, as long as it works I will be happy. Thanks for trying to explain it.
Feb 01, 2003, 10:56 AM
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ferradas's Avatar
I'm not an electrician either but from what I understand, the bow uses AC current which is what the transformer supplies, if you notice the diagram, directly out of the transformer you go into the bow, you are supplying AC to the bow, then, the IN4001 rectifier converts to DC so the voltmeter can read the voltage rating. Something like that.

I cut another core yesterday using pink Foamular 250 and it cuts nicely at about 4 volts on the voltmeter.
Feb 01, 2003, 01:18 PM
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Thanks for all the help. I have never cut any cores so this is all new to me.
Feb 01, 2003, 05:26 PM
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ferradas's Avatar
me too man, you gotta fish for all your answers.
Feb 03, 2003, 03:57 PM
The flying squirrel!
Mr.Dickles's Avatar

Ground wire? What type of power cord?

Hi guys. I am almost finished with my cutter PS. Something in the instructions was unclear and I was wondering if someone could help me out.

1. What IS the correct way to connect the secondary outs on the transformer to the bow connections? I am using the transformer in the instructions, it has two yellow wires and one black wire. From some of the posts earlier it looks like I want to use the black wire and one yellow wire for the bow connectors. Is there a difference in which yellow wire? Im assuming one is 12V and the other is 26v?

2, Second question was regarding the use of a ground wire. Radio shack didn't have the power cord that was listed in the original instructions (I think the product number is wrong or they dont carry it anymore) so I'm not sure what kind it is: two prong or three? If its three pronged, do I attach a wire from the third 'ground' wire on the powercord to the transformer case? Should I solder it somewhere on the case, or should I put a connector on it and put in on one of the bolts that hold the transformer into the powersupply case? My friend said it was NOT totally necessary to use the ground wire, but I thought I might need it for safety. (my apartment is old and not properly grounded anyways.... yeeesh!)

Thanks again for all your help folks!
Feb 03, 2003, 08:56 PM
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ferradas's Avatar
Ken, here's a diagram that I drew up. You need to use both yellow wires off the transformer to the bows and don't use the middle black wire, cut it and put tape on it.

You can use any extension plug you want. 2 or 3 prong (grounded). If you use 3 prong, the ground wire goes to the transformer case, anywhere you want as long as it's touching the case.

I added a 115v plug to my unit in addition to the banana plugs. It was very easy to do, just splice from the wires going to the banana plug and route them to a wall socket plug.

Here are some pics.
Feb 03, 2003, 08:58 PM
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ferradas's Avatar

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