[ARC5] Need Help with Variac Diagnosis

[Kenneth G. Gordon]

On 19 Feb 2015 at 18:16, Phillip Carpenter wrote:

> 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.

Yes. Look at it very carefully: all it would take is for one winding to be shorted 
out. If that is the case, the longevity of your Variac would be compromised.

> I'm debating whether to hard wire the inrush current limiter in series on the
> input side

I would be wary of doing that: if that inrush limiter is the kind I think it is, then 
it can get very hot at full current through it.

> or whether I should add it via a switch like Ken did with the
> resistor so I can switch it out after startup.

I didn't use a switch: I used a time-delay relay, which I installed inside the 
Variac case so there were no external indications that it was in the circuit.

I bought a number of 115 VAC time-delay relays off eBay at a low price.

> 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.

Yes, and that is the problem: it heats up, and the amount of heat depends on 
the current drawn. Those things can get so hot they burn wires which are too 
near them.

> 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?

What is the input voltage to your transceiver? 110VAC or 220VAC? What is 
your normal line voltage? How much do you want to drop the voltage? To 
what voltage? At what current?

Ken W7EKB