[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] solid state varaic



Paul Bidmead wrote:
Scott,

this is how most large ups's are built the difference from them to vfd's is that the output V/F is adjustable

this being simple in theory the practical implication can be quite unstable / expensive in comparison the the cost of a simple variac... not saying it cant be done but for the general hobbyist it can be quite daunting


Paul B
Greetings all,
So I'm wondering if it would be possible to make a solid state variac in a similar manner, the advantage would be light weight and I would assume it would be much cheaper when dealing with high powered systems, the disadvantage is I don't think it would be possible to get the 140/280V output like you can with the real thing.


Yes.. I've done it.. I used a bridge rectifier in series, with the FET as the pass device in the middle driven by a 555 biased by a couple 9V batteries. (hook the FET from the + to - terminals of the bridge, the two AC terminals go to line and load)

It works, but...

You need a fair number of components to make it work well and smoothly vary. It generates copious RFI and is quite sensitive to destruction from transients. The variac is a pretty convenient device.. robust, cheap, etc. Where I used to work, we'd buy 5A variacs for about $60 each in quantity, and we couldn't get the FET equivalent down to that, by the time we got the parts, assembled, etc.


_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla