First variac, rebuild - Page 1
Forum section: electronics / general

author: electronics-whiz
author_rank: Regular Contributor
timestamp: January 16, 2015, 09:09:41 pm
content: I was working on a project the other day, asked a friend I could barrow a variac again. He said if I can find one, we found one, he pulled one out from a pile of stuff, said here keep it. This would probably be tossed when move into new building anyway.One of the really old standard electric Adjust-A volt models. Main cord was two prong non polarized, socket was polarized though. It worked fine as is, but I didn't like. I had a 3C cord from a microwave that failed, replaced the line cord and soldered it all up, connected GND to mounting screw for the terminal block. I thought about replacing the socket, but most sockets aren't round, and was low on space in the connection box. I then just took a wall adapter and soldered some 14AWG wire to the tab and put a screw terminal on other end and screwed that to one of the transformer cover screws.Then I did ohm test to see was wired right, all the GND was good. It was all good. Got a free variac and hour of work it's all up to date, and feel safer using it. I may build some sort of unit to go with it that will hold a 7+ amp rectifier and a few filter caps. I have a 0-140V DC supply for whatever.

author: GreyWoolfe
author_rank: Unknown
timestamp: January 17, 2015, 04:18:17 am
content: Good for you. Enjoy using it.At our last ham club meeting, someone came in with a 10A variac and said here, enjoy. You just need to replace the power cord because the insulation was cracking. As it was already 3 prong, a simple cord swap made it just like new. I thanked him profusely.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: January 18, 2015, 05:13:25 pm
content: That's a nice score. mines only a 7.5 amp, but can't really complain about that, and many they have were like 3A, or were 0-120 without the additional 20V overdrive.I may take the cover off too, and look at the transformer part. Some reason at like 40 and 100V there is something that it like clicks into. Feels like a DMM dial clicking into something. Why these positions I have no idea, only guess I have is it's some sort of like safety protection. The winding, brush looks fine, so seems some other thing doing it.

author: Yansi
author_rank: Super Contributor
timestamp: January 18, 2015, 05:20:21 pm
content: I've also scored one from junkyard some time ago. It is a 2.5kVA monster. It's 220V nominal input, with overdrive to I think 250V. (which goes up to 260 with the mains voltage we use now)

author: electronics-whiz
author_rank: Regular Contributor
timestamp: January 18, 2015, 07:05:19 pm
content: Some pics of my Variac.top two are after the updates I made. Bottom one is original cord which was in good shape, but not polarized or grounded. New cord is about 1/2 the length, but I figured most likely use on my bench anyhow and I can always use extension cord if need longer.

author: aaronwhite30
author_rank: Newbie
timestamp: January 27, 2015, 04:05:27 am
content: I actually built a metered variac out of a 3A commercial rheostat and an amp and voltage meter across the primary spending only $80 for the whole shootin' match.