Cheap 20amp 110vac to 150vac variac where?

[rmay635703]

Anyone know what happened to the old variacs that can boost voltage?

I'm hoping to find a 20 amp unit with 110vac in and 150vac+ out

Most don't seem to top out around 1:1 in out but those that go into boost are way larger and usually go to full 220vac out, which I don't really need.

Any ideas?

[shovel]

There are a number on ebay... 20A units appear to be in the $150+ range but they appear to exist.

[oil pan 4]

I was searching for a bigger version of my 5kw 240v input 300v output auto transformer not that long ago and all I could find were those small 120v in 140v out units on ebay.
Most of the 120v ones are not 20 amp.

[Stubby79]

Do you need a set voltage, or an adjustable one?

[oil pan 4]

For lower voltage I just rewrap the secondary on microwave oven transformers.

[rmay635703]

Originally Posted by Stubby79

Do you need a set voltage, or an adjustable one?

Honestly a set voltage would be fine, but sadly I need to find what it is. (It's between 140-160 volts) the 220vac output variacs seem to be much larger and more expensive than I would prefer..

The 140 volt units seem to not go past 1:1 which makes them useless to me.

Being able to put in either 110vac or 220vac and get around 150 would be nice but not necessary.

Thus far there only seem to be 2 main styles of variac and the ones that boost aren't in those common categories.

Ah well

[ThermionicScott]

150ish volts at 20 amps is a lot of watts! What are you looking to do?

[Stubby79]

Originally Posted by rmay635703

Honestly a set voltage would be fine, but sadly I need to find what it is. (It's between 140-160 volts) the 220vac output variacs seem to be much larger and more expensive than I would prefer..

The 140 volt units seem to not go past 1:1 which makes them useless to me.

Being able to put in either 110vac or 220vac and get around 150 would be nice but not necessary.

Thus far there only seem to be 2 main styles of variac and the ones that boost aren't in those common categories.

Ah well

You can use an isolated AC source to add it's voltage to another AC source, as long as they're in phase with each other...

...meaning if you had a 120v to ~30V AC transformer, you could put it in series with the 120v from the outlet, and the two will add together to give you 150v AC. As per this informative article (which I would not recommend for complete novices to follow):
Battery Charger Schematic (Bad Boy)

You could also use an isolation transformer instead of straight-from-the-wall power to completely isolate it. Or combine a variac with an ~30v (isolated) transformer to give you the ability to alter the voltage.

Please note that a variac IS NOT ISOLATED...and trying to combine it in series with it's own source will end in the apocalypse...at least as far as you and anyone in the room with you is concerned anyway. Wasn't there something about not crossing the streams in ghost busters? Well, this won't have a happy ending...

Be safe! (and if you don't need this warning, well, some people out there reading probably do)

BTW, what are you trying to accomplish?

[RedDevil]

The reason you don't see many variacs around anymore is that for most appliances you get better control and efficiency with a triac which is cheaper too.
As a driver for brushless motors, not so much. But otherwise I'd go with the 220 Volt transformer, then bring it down to your desired voltage with a triac.

[rmay635703]

Originally Posted by ThermionicScott

150ish volts at 20 amps is a lot of watts! What are you looking to do?

Actually, my source will be a 20 amp outlet the output will use a max of 12 amps.

So I shouldn't exceed 16 amps on the supply side (even with losses)