Variac

[Bushbaby]

Hi All,
I'm thinking of buying a variac of which I know very little. I'll assume that I need one to 240V output but what sort of ampage do you recommend?

I was think of something like this from ebay

Item number: 290534883755

Whats the chances of picking up a cheap one at a radio fair???

Regards

Rob

[OldTickTock]

I've had mine over 12 years and is a 2A Zenith, served me well on radios and now on TV's. I've built mine into the bench and added a voltmeter and extra plug sockets. It actually goes up to 260V. I think you will find most go over 240V. I'm sure the test gear guru's like Rob (glowinganode) will have more extensive advice to provide you with to make a more informed choice.

Chris

[Bushbaby]

Hi Chris,
Do recommend buy one from new?

Regards

Rob

[OldTickTock]

It's your choice, Victor VanTickTock hates new so always goes for something vintage. Igor prefers it too

Chris

[glowinganode]

My bench variac / isolating transformer is rated at 2A / 500VA, which is plenty for most jobs.
I've also got a 8A unit that I hardly ever use.
Radio Rallies are always a good place to look, expect to pay £10-15 for an uncased or around £20 for a cased one.
Most important thing to check is the "track", look for arcing or burning. Check the graphite brush too, though these can be replaced.
When you turn to knob, you should get a nice smooth feel across the entire range with a slight buzzy sound / feel. If it's at all notchy, walk away.
Rob.

[Bushbaby]

Hi Rob,
Thanks for the very valued advice

Regards
Rob

[beam me up schottky]

My advice would be to go for a portable cased version, this makes it very convenient to test stuff away from the bench, something I've found myself doing quite frequently ! Mine is a Zenith, has a normal mains socket on the side, a voltmeter on the top and is rated at 3 amps, never needed any more than that. It is a vintage one, probably 40 years old at least, in a very nice, ventilated cast aluminium case. They don't make them like that anymore, as they say.

[Skywave]

Just to add a helpful comment.
When you do install it, make sure you fit an adequately rated anti-surge fuse in series with the primary (at least): it's easy to overlook this during the excitement of installation. A "Variac" has the most hardest time when the ratio between Vin and Vout is large, since under those conditions it is the common part of the winding that is doing most of the work. Consequently, when inspecting a "Variac" for intended purchase, check for smoothness of operation at the ends of the rotation. Since "Variacs" are most commonly used to provide 110v / 115v from 230v / 240v, it is also the approximate centre of the windings where overload damage is most likely also; usually manifest by darkened areas of enamel on the copper windings.

Finally, and just as an aside, the name "Variac" is a registered name of the Zenith Corp. A bit like the word "Hoover", where one name has become synonymous with all makes of a given product.

Al.

[beam me up schottky]

Good advice there Al.

Just a little thing though, I thought Variac was a trade mark owned by General radio ? Also, I've always understood Variac to be short for variable AC ?

[tiv48]

mine is a 2.5 amp job from maplins about 10 years ago built into a case with a cap reformer 2 amps should be plenty above this they tend to be big heavy and expensive, i did try a dimmer switch but the one i used was no good on anything with a mains transformer
rob t