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

RE: [TCML] Variac

dave - you are right about lamp inrush currents, but incorrect about protection in this case.  Let us consider - can the OP turn on a desk lamp with a 100 watt bulb (yes, of course he can) - now, put a variac in series with the desk lamp - the variac cannot have a negative characteristic, so the worst case is zero resistance which reduces to the prior case - e.g. it is no worse than turning on the lamp in the first place.  
> Date: Wed, 29 Oct 2008 14:35:09 -0500> From: dave@xxxxxxxxxxxxxxxx> To: tesla@xxxxxxxxxx> Subject: Re: [TCML] Variac> CC: > > 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> >> _______________________________________________> Tesla mailing list> Tesla@xxxxxxxxxxxxxx> http://www.pupman.com/mailman/listinfo/tesla_______________________________________________
Tesla mailing list