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[TCML] Re: Variac troubles

Hi Jay,

Not sure if I can really help yet...

But are you running this on single phase or 3 phase input?
Not clear with info you gave so far.

If 3 phase supply, what is the type exactly?

So if using single phase, did you rewire the 3 cores and get and use the 3
required chokes?

You are already on the expected inrush when they are big like this and
various methods to try to deal with this... but if there is a problem

Are you using just "standard residential" breakers?

There are industrial motor delay types available, but not likely to be the
same type to fit into a standard residential breaker box. So would require
a different high main supply branch and then these motor delay breakers in
it's own breaker box.

So a few more details needed and a few suggestions from me here.

And I am sure some others more knowledgeable on variacs will soon chime

Chris Reeland

Sent from my Samsung Galaxy Tab® S

On Sun, Aug 8, 2021, 7:39 AM jhowson4 <jhowson4@xxxxxxxxxxx> wrote:

> All, I would like to pic your brains. I acquired a stacco 5010-3Y, its
> labeled as a 240V 3 phase unit set at 0-280 out. 50A per core. Only 3
> terminals per core. Clearly marked. I'm running it on a 30A breaker at the
> moment. With no load you'd think that would be fine. Sounds great, except I
> can't get the darn thing to operate. Pops the breaker every time. Makes a
> hellacious 60hz hum in the process on all the cores. This is with it
> connected to nothing on the output, just applying voltage. Logically I
> checked for anomalous resistances, everything showing proper
> isolation.Visual inspection doesn't show anything noticable, Brushes and
> contact surface looks good. One of the cleaner units i own..  Inrush
> current seemed to be the next logical thing to try, got a 35A CW rated
> varistor 2 to.02ohms (i only wanted to run these at 30A for the time
> being)  which promptly exploded.  A relay shorting a high power 6ohm
> resistor was the next step. Powered on at 240v with series resistor for
> about 5 seconds then kicked on the relay to remove the resistor, bzzzzzzz
> pop goes the breaker. No magic smoke or smells of burnt enamel.
> Unfortunatly I havnt been able to observe the actual current its drawing
> yet. But I will set up a scope in the near future to record it. I've
> brought many variacs back into service, as have many of you. But this is
> the only one thats been a real head scratcher. Next step is to pull the top
> plate and see if anything is going on in the middle with the connections,
> but alas Its not like I'm reading any shorts. There are 3 little inductors
> or something that seem to be inside each core. I assumed they were on each
> input/output to act as a current limiter of some sort.  But ill have a
> better look when I pull the cover and go over a core with a fine toothed
> comb.Anyone have any ideas of what I could be looking for or potential
> causes. What ever the matter is, it seems to effect all 3 cores. Unclear if
> the effect is equal on each core, but the result is the same. -Jay
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