RE: [TCML] Variac

["Lau, Gary" <Gary.Lau@xxxxxx>]

If a cold lamp filament had too low a resistance to achieve the desired current limiting effect here, then that lamp would be tripping the breaker every time IT was switched on.

You really don't need much resistance at all to eliminate the nuisance tripping.  I noticed that the turn-on surge would only trip my breaker if the Variac was plugged in to a socket in close proximity to the breaker box.  If it was in a remote room or had an extension cord, it never tripped.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of David Speck
> Sent: Wednesday, October 29, 2008 3:35 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Variac
>
> 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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