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Old 4th Nov 2006, 4:26 pm   #1
Bob_Moss
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Default Economy Variac. Is this a good idea?

If you were to connect a cheap and nasty light dimmer to a radio via an isolating transformer, would the transformer help restore some sort of sine wave, whilst isolating the test radio from the mains?
This could provide a cheap and safer pseudo variac.
Has anyone out there tried it, or have you got more sense?
I'd like to give it a go but my 'scope's on bricks at the moment.
Comments please.

Bob.

Ps you could use an in-line mains filter as well I suppose.
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Old 4th Nov 2006, 4:44 pm   #2
ppppenguin
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Default Re: Economy Variac. Is this a good idea?

Not recommended. The nasty edgy waveform from the dimmer will annoy the transformer with unpredictable results. The tranny certainly won't restore the waveform to a nice sine wave.
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Old 4th Nov 2006, 5:43 pm   #3
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Default Re: Economy Variac. Is this a good idea?

Hi Bob, I wanted to use an infra-red remote controlled lamp dimmer for turning on power to a transformer but it did not work. The dimmers are meant for mainly resistive loads and shut down if the load is too inductive. I tried to cheat it by making it control a mains relay with a 15W lamp in parallel. It worked but clearly did not like it as operation was a bit hap hazard and the whole set up buzzed loudly. In the end I bought a radio controlled 13A socket. I have a 10 Amp variac which I use mainly for servicing switched mode power supplies in conjunction with an isolating transformer, if you just want to service valve radio's etc. then the series ballast lamp method has a lot to commend it.
Les
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Old 4th Nov 2006, 7:41 pm   #4
Superhet Si
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Default Re: Economy Variac. Is this a good idea?

Most light dimmers crop the sine wave with a Triac , causing problems with massive noise on the supply.
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Old 4th Nov 2006, 8:14 pm   #5
Steve_P
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Default Re: Economy Variac. Is this a good idea?

Bob - for all the reasons listed, in answer to your question....

NO !!!!

I tried it....

Steve P
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Old 29th Nov 2006, 1:55 am   #6
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Default Re: Economy Variac. Is this a good idea?

And many lamp dimmers still arent inductive rated. Chinese variacs are not dear these days!!
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