[Prev][Next][Index][Thread]
Large Variac Help
From: gweaver[SMTP:gweaver-at-earthlink-dot-net]
Sent: Sunday, January 11, 1998 3:16 AM
To: Tesla List
Subject: Re: Large Variac Help
At 11:45 PM 1/10/98 -0600, you wrote:
>
>From: Barton B. Anderson[SMTP:mopar-at-mn.uswest-dot-net]
>Sent: Saturday, January 10, 1998 2:09 PM
>To: Tesla List
>Subject: 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 first
>expected a wire short, but from all the other tap to
>tap measurements, there would have to be multiple
>shorts between each. This does not seem probable. It's
>got me a bit confused. The winding core is epoxied to
>a metal base, but there's no short between base to
>windings. There's no burnt smell and no visible burnt
>wiring. I assumed the amount of wire wound would have
>to read larger than 0.6 ohm dc resistance? Has anyone
>with a large variac measured dc resistance with the
>same results? I don't feel comfortable plugging this
>in yet. Do I have a reason for concern?
>
>Any comments greatly appreciated,
>Bart
Try connecting the variac in series with a 100 watt light bulb and see if it
will vary the brightness of the bulb when connected to 120 vac.
3 of my 7 variacs were bad when I got them. One had a broken wire at the
center tap terminal and when I reconnected the wire it worked. The 2nd
variac didn't work because the wires were dirty where the brush rotates on
it. I sanded the wires with 400 grit sand paper and fixed it too. The 3rd
variac was out of adjustment. The brush didn't touch the wires.
Gary Weaver