[ARC5] Need Help with Variac Diagnosis

[Mike Feher]

Is it possible that you do not have it connected correctly? There is minimal
inrush current with no load, makes me think you used the wrong taps for the
input. Regards - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 


-----Original Message-----
From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Phillip
Carpenter
Sent: Thursday, February 19, 2015 2:01 PM
To: <arc5 at mailman.qth.net>
Subject: [ARC5] Need Help with Variac Diagnosis

I have a General Radio W20MT3 autotransformer, this one handles 20 amps, or
about 3,000 watts. It came without meters so I've added a Simpson AC
voltmeter in parallel on the load side and a matching Simpson Ammeter in
series with the reset beaker on the load side.

I'm having two issues: 1) the unit trips my 20A house breaker at no load. I
believe this is caused by inrush current so I have ordered a 20A inrush
current limiter to help solve that problem. 2) originally the voltmeter read
120 volts when the Autotransformer was rotated full, but now it only reads
117 volts. If I switch the output to 140 volts the voltmeter only reads 134
volts. Something has started acting like a resistor and dropping the
voltage.

Does anyone have an idea what could be causing this? I plan to use this
Autotransformer to drive my tube radios, such as the ARC-5s, as well as my
Hallicrafters SR-2000 ( which is why I have the 20A version). The AC voltage
here runs 120-121 volts, so I want to roll it back to 115-117 volts.

I can't figure why the output voltage dropped below 120 or 140, depending on
the winding setting. Could there be some metal shaving has fallen into the
winding that is shorting it?

Any thoughts from those with experience using a Variac is very much
appreciated!

Phil

Sent from my iPhone
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