Vari-AC failure modes

[ruairioflaherty]

Hi all,

I picked up a Powerstat autotransformer a little while ago at a yard sale.  I needed to use it today for the first time.  I connected it to a working compressor that I was investigating and with the control knob at 100% I was getting only 95 VAC at the IEC input to the compressor (I was getting a normal 118VAC when the comp was connected directly to the wall outlet).

When I started dialing back the Vari-AC control the AC voltage actually started rising until it reached about 105VAC (with the knob at 85%) and then started dropping again.

I have almost no experience with Vari-AC, is this unit beyond repair or is there something simple that could be done to rehab it?

Edit - this is the exact model I have - http://www.gsisinc.com/posecom/products.php?product=PowerStat-3PN126-Variac

 

[moamps]

You should first check your Variac using a bulb as a load. If the voltage cannot be smoothly regulated, you can try to fix it by cleaning slider and whole contact area on the autotransformer.

https://www.youtube.com/watch?v=ixKNrLjv91Y

 

[ruairioflaherty]

Thanks Mo,

The unit failed the lightbulb test badly.  I'll take it apart tonight and see if I can clean everything.  I bought this for $15 but the used prices I'm seeing for the same unit are closer to $200 so it seems like it will be worth some parts if needed.

Cheers,
Ruairi

 

[emrr]

The contact brush will go, pull it out and see what it looks like.  Usually spring loaded. 

 

[dfuruta]

I see these fairly regularly with burnt windings.  If that's what you've got, it might be possible to either splice around it or to use different output taps to skip that section.