Large Variac Help

From: 	Adam[SMTP:absmith-at-tiac-dot-net]
Sent: 	Sunday, January 11, 1998 2:02 PM
To: 	Tesla List
Subject: 	Re: Large Variac Help

>I have a Variac I think is shorted. Here's the specs:
>GE, Input 120/240V, 50/60Hz, 1PH, Output 0 - 240/280V,
>30 Amps.

>There's 7 taps and #3 is the variable output tap. My
>problem:    I'm measuring winding dc resistance and
>the Fluke reading 0.6 ohms at pins 1 and 4 (full
>winding). Measuring all the other taps from tap #1
>common as well as all other combinations is below 0.6
>ohms. I don't have a lot of experience with variacs,
>but something tells me this isn't right.
>I assumed the amount of wire wound would have
>to read larger than 0.6 ohm dc resistance? 

You know what they say happens when you assume. :-)  The resistance is 
below the accuracy of your meter.  The inductance is significant and 
easily measureable, but the DC resistance is (and should be) very near 
zero.  Why are you measuring the resistance anyways?  If you are trying 
to find out if it works, apply a low voltage like 12.6 volts to the 
input, and sweep the knob.  Put your voltmeter across the common terminal 
and the moving tap, and check to see that it sweeps linearly from zero to 
a max of about 17% over the input voltage +/-2% without any surprises.


Adam Smith
Epoch, Inc. Digital Music Project

www.tiac-dot-net/users/absmith/                 MP3 Demo Tracks Now Available!