[ARC5] Need Help with Variac Diagnosis

[Phillip Carpenter]

Mike,

I am pretty sure I have it wired correctly. I have the manual for the Autotransformer and I wired it as per the manual.

I believe Ken has the right answer to my problem #2. There must be some metal shaving or a loose washer that has fallen into the winding shorting it near one end. That would explain the decreased voltage reading. I'm going to take it back apart and after I carefully inspect the winding blow it out with air pressure and see it anything comes out.

I'm debating whether to hard wire the inrush current limiter in series on the input side or whether I should add it via a switch like Ken did with the resistor so I can switch it out after startup. I'm not sure I want to drill anymore holes for another switch. The inrush current limiter (thermistor) is supposed to be able to stay in the circuit all the time. It's resistance drops to zero as it heats up.

Many thanks for the discussion.

I'm going to look at bucking transformer setup too. But I'll need one that can handle up to a 2000 watt transceiver. Any ideas on what bucking transformer to use for this situation?

Respectfully,

Phil

Sent from my iPhone

> On Feb 19, 2015, at 2:05 PM, Mike Feher <n4fs at eozinc.com> wrote:
> 
> 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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