Foam cutting - electronics question AC to DC - RC Groups
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May 01, 2001, 10:52 AM
I'm disoriented!
ChrisD's Avatar

Foam cutting - electronics question AC to DC

I made a power supply for a foam cutting bow using a ceiling fan speed control and a Radio Shack 2 amp transformer. The transformer output is 24 volts AC at 2 amps. I tested the setup yesterday with a .022 diameter stainless steel fishing line. Works great in test, but not sure how it will work on a 24" wing core.

My question - should I put a bridge rectifier and a couple of capacitors on the output of the transformer to convert it to DC? Will this make a difference in wire temperature/amp draw???

I've read all the posts about using a car charger, ESC/Nicad pack, variac, feathercut etc. already, and they are next on the list of options. Total cost - $20 in parts.

Thanks, Chris
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May 01, 2001, 10:57 AM
Registered User
AC heats things up just as well as DC, after all electric fires work on house AC. There's no value in complicating it further. The only thing I'd be a bit wary of is the 2A transformer. The rating seems a little low, I'd check from time to time to see if it's getting hot !

May 01, 2001, 11:01 AM
I'm disoriented!
ChrisD's Avatar
Thanks, Steve,

I don't expect the cuts to be that long in duration, or making lots of them. The transformer was $9.99. I'll give it a shot.

May 01, 2001, 12:58 PM
Frequent User
yb2normal's Avatar
The primary advantage of a DC voltage is safety... AC voltage travels through your body much more efficiently.

I combined a couple of the suggestions from ezone (including yours interestingly enough), and plugged a cheap car battery charger into a high power light dimmer... The result is safe, isolated DC current, and as a bonus I can read the current draw off the meter on the charger. I simply adjust the light dimmer until the charger says that I'm drawing about 4 amps, then start cutting.
May 02, 2001, 01:28 AM
I'm disoriented!
ChrisD's Avatar

Hey, I've got a 12v Deep Cycle 10 amp charger as well.

I thought about it, but dismissed the idea because I couldn't control the amperage. Your solution sound great. I'll try it with my fan control. Yes, the charger has a meter as well. It didn't dawn on me to use it. duh!

May 02, 2001, 06:11 AM
Registered User
I don't think 2A@24V is short. I use a 70 cm bow, with stainless steel (0,3mm I think) and use a power supply with adjustable V and A.
To cut the foam with your setup just put the wire over the foam, and increase the power; as soon as the wire starts to cut, you have your "good" point.
In my setup, this takes 2,5 A @ 12VDC, which is about 30W. You have 24V x 2A = 48W.
It depends on the wire you're using, but turn of the power as soon as the cut is done, and I think you could use more power (I would say 60-70W, for 30-45s period).

About AC and DC: there's no problem at all. For security reasons, try to connect one AC line to earth. This way you should have no problem, even if the transformed fails in service...