Re: [TCML] Variac

[David Speck <dave@xxxxxxxxxxxxxxxx>]

Actually,  a light bulb has the wrong temporal characteristics for your 
application.  A cold lamp filament has near zero resistance, and may not 
protect you much against an inrush surge.  A 10 ohm 100 Watt resistor 
can't be more than a buck or two at a hamfest or surplus place. 

To implement, wire the power resistor in series with input leg of Variac 
(black wire to power switch to the wall plug).  Wire the two normally 
open relay contacts across the two ends of the resistor.  Wire the coil 
windings of the relay between the black output terminal of your power 
switch and the white return wire to the wall plug.  When the relay coil 
pulls in, it shorts out the resistor.  Only takes a few AC cycles, but 
that's all you need.  That's all there is to it. 

As far as depotting the Square-D transformer, as they say, just 
fuggeddaboutit.  That's a glass filled epoxy potting, and you will 
destroy the windings, shred your fingers, and lose your temper long 
before you get the stuff off, not to mention wasting hours of 
frustration.  Go look for a bunch of discarded microwave oven 
transformers and you will be way farther ahead with a lot less work.  
See previous postings on series connecting these MOTs into very usable 
TC power supplies.

Dave

jhowson4@xxxxxxxxxxx wrote:
> the light bulb sounds like a much cheaper idea for me at the moment. but i am still curious about the relay thing.  could you possibly draw a diagram.  I am a visual kind of person. thanks
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