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question about Variac use

Just got one for use with a fret burner. Since it is a power supply usable several ways, is it a viable idea to put a dimmer switch between the Variac and whatever is being powered? That way you could set the voltage on the Variac, but do the controlling with the dimmer, the dimmer maxing out at the set voltage. With proper operation, you'd never blow anything up, the power can never go overlooad.

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Permalink Reply by Timothy Hunter on November 27, 2019 at 7:46am

im with Cause here. not a safe way at all. if you want to use nichrome wire to burn fret markers there are safe ways. https://www.youtube.com/watch?v=qzaHd-BmROA

this video shows using a 9V battery. notice how hot, glowing red the wire gets! that will seriously burn you if not careful. the video also shows how you dont need a lot of voltage to make the wire hot enough to burn wood.

what you need is a cover that closes a switch when closed. as well as 2 other buttons in series,one either side of the cover. make it so the wire can not get hot unless all 3 switches are closed. ie place the wire where it is to burn. close the lid press the left switch with the left hand and the right switch with the right.

this way you can not ever burn anything accidentally.

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Permalink Reply by James Pobog on November 27, 2019 at 12:56pm

Kinda complex, but I understand the interlocks. Maybe a micro switch with a couple intermittent push buttons...

The 'build stuff to be able to build other stuff is piling up...

Permalink Reply by John Sawyer on November 27, 2019 at 11:05am

I've used a hot wire for years to cut foam for model airplanes. The first thing you notice is his use of a 12V battery charger. This doesn't eliminate the burn risk, but brings the voltage to a safe level.

Modern battery chargers are electronic, and won't work... you need an older one that doesn't auto-cutoff or look for a battery. (Basically, see if it produces 14ish volts with nothing connected on the battery end.)

THEN you can use your variac to reduce the voltage to what you need...

And no, a household dimmer is not necessary...

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Permalink Reply by James Pobog on November 27, 2019 at 12:48pm

OK, what about 6 volt lantern batteries, with an on/off switch?

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Permalink Reply by James Pobog on November 27, 2019 at 12:58pm

The whole idea of the dimmer was to act as a safety. If the Variac was set to 9-12 volts, doesn't matter what you do with the dimmer (or light switch for that matter) voltage will never go over 9-12 volts.

So is it the AC that everyone is worrying about? I can sell the variac on ebay...