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[TCML] Re: Variac troubles



Hi Jay,

I think Bert has "hit the nail on the head".   :^)

These are individually 120v input each when not 3ph Y setup, and I am
agreeing after looking at the current catalog of my stacks and your stack.

You could very easily series two for 240 input, is an option...

I just took a look at my Staco stacks. I have models 5020's (2 parallel)
and 5021's (3 parallel).
Both 240v input.

Current catalog model is 5021. 5020 is an older design of same I think.
These 5020's of mine are "slightly older" looking than my 5021's.  But
otherwise identical looking. What the difference is not physically apparent
to me.

So something similar 5010 vs. 5011 I'm thinking.

Chris Reeland
Ladd IL USA

Sent from my Samsung Galaxy Tab® S

On Sun, Aug 8, 2021, 2:10 PM Bert Hickman <berthickman1@xxxxxxxxx> wrote:

> Hi Jay,
>
> Try running them off 120 volts to see if they operate correctly.
>
> Although I wasn't able to find the specs for your specific variacs, Staco
> does show what may be a similar version (5011-3Y). Deciphering the part
> number suggests that your ganged variacs may be actually be configured to
> operate off 120 volts. Staco's varics often have a variety of
> terminals/taps that allow them to be configured for operation in various
> single-phase and 3-phase modes and ganged for higher currents.
>
> The chokes are likely "paralleling chokes". These are are actually small
> transformers that are used to balance slight output voltage differences
> when
> multiple variacs are connect4ed together to increase output current and
> eliminate unwanted circulating currents between paralleled variacs.
>
> Once you remove the covers, you should be able to rewire them to operate
> of
> 240 volts by changing jumper settings. The Staco web site has lots of
> information that you may find useful.
>
> Good luck!
>
> Bert
>
> 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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