Building a variac

[bereanbill]

building a variac

Hi again..anyone have plans for building a variac ? How hard can it be ?

 

[Brett]

Why would you bother? They're cheap enough second hand.

 

[bereanbill]

I guess just for the sake of accomplishment...

 

[zman3]

I'll have to agree with Brett; there are many other things you can do in this hobby that would fill you with a greater sense of accomplishment for far less money and/or aggravation (custom winding an output transformer or building a line-level preamp both spring to mind).

Just in case nobody has mentioned it, try to attend a local hamfest. I've picked up 10 A variacs fused and in housings for as little as $5 - and I can assure you they're FAR safer and more reliable than anything you can build.

 

[Robert McLean]

Here is a possible compromise answer :
Buy one of the cheap readily available variacs, you will have a good safe one, as Brett and Zman3 suggest,
then
copy it, and your desire for a sense of accomplishment will be satisfied.

 

[Brett]

I didn't mean to rain on anyone's parade, but for the same effort you could wind your own audio transformers which will teach you more and you'll get a lot more use out of. I use my variac a bit, and on a busy week it'd be lucky to get an hours use.

 

[bereanbill]

Thanks for the input. Winding trannies is on my accomplishment list, but I don't think I'm quite ready for it yet...baby steps first. I'm kind of a Rube Goldberg-type, so anything is gratifying to me. With the clunkers I have around, a variac will get quite a workout in my laboratory.

 

[Brett]

Some reading for you then.
Turner Audio Educational pages

There's quite a bit on load matching, as well as OPT design info a bit further down.

 

[Iain McNeill]

I have to reinforce the sentiment here...

A variac is an instrument of death (anything that connects directly to the mains is lethal) This isn't a good choice for a 1st build.

Buy a good safe one and it will help protect you during your other experiments

 

[TubeMack]

Any recomendations? I just picked up one as a part of a test equipment buy. It looks to be from the 30's,and the cord appears to have caught fire! I'm guessing I shoud just junk it. I'd like something newish and cheap.

 

[Brett]

Any recomendations? I just picked up one as a part of a test equipment buy. It looks to be from the 30's,and the cord appears to have caught fire! I'm guessing I shoud just junk it. I'd like something newish and cheap.

If in doubt about it's safety, don't use it.
Variacs are on ebay all the time, new and used quite cheap.

 

[nhuwar]

Any recomendations? I just picked up one as a part of a test equipment buy. It looks to be from the 30's,and the cord appears to have caught fire! I'm guessing I shoud just junk it. I'd like something newish and cheap.

Why junk it just check it out real well and replace the cord.


As for building a variac, I sort of tried it when I was young before I knew that transformer core had to be made of laminations. I wound it on a tee post with about 400 to 500 turns and hooked it to 120 vac and pow the breaker tripped.

It was a good learning experience and it made a good electro magnet LOL.

I got the idea from a hipotronics voltage regulator which had a long variable transformer. It was about 3 feet long and not a toroid. It drove a buck and boost trans.


Nick