New Variac for Joule Electra Amps

Outlier,

Is your Variac one that self-adjusts to keep the voltage constant within a fairly tight tolerance? Possibly made by Monster?
http://www.amazon.com/Monster-Cable-MPPROAVS2000-Channel-Conditioner/dp/B0002ZO5W2

Or is it the type where you set it manually to raise or lower the voltage for the desired loaded output voltage of the unit?

Does you mains voltage fluctuate a lot? Or are you just trying to compensate for a too high or too low of a voltage? If the latter you could use a buck/boost transformer configured as an autotransformer to solve the voltage problem

Outlier,

Sounds like you slowly ramp up the variac with the amps connected, powered on, and then set the desired voltage under load. This action over time will cause wear on the brush that contacts the autotransformer winding directly proportional to the connected load of the Joule Electra amps.

First I would not try to use the variac until you have it checked out. It could be something as simple as a fuse holder as Thaluza stated in his post. Or maybe even a loose connection. Or it could be more serious like a bad brush on the dial slider arm that contacts the winding of the autotransformer. If that is the case hopefully the autotransformer winding is not damaged.

If you are the least bit mechanically inclined you could pull the cover from the variac and have a look inside.... Make sure the variac is unplugged from the mains AC power before you start.... You could then see where the problem is. Look for a burned spot that will more than likely show signs of black carbon and will have a burnt smell.

Here is a nice video I found doing a Google search.

https://www.youtube.com/watch?v=M8cJrJyR87o
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Jim

Outlier,

It's toast! It is not worth repairing in my opinion. I would just see what a new one would cost. A new one will come with a warranty.

The variac is the latter; manually 'dialed up' to operating voltage of approximately 166 volts.
12-09-14: Outlier

166 volts? Why so high? Does the power amps have a regular US 15 amp 125V plug on the end of the cord?

You can buy variacs all day long that go up to 140V that plug into 120V mains power.

Somewhere on the variac should be a data plate showing the input voltage and the FLA, full load ampere rating of the unit. It should also list the max output voltage.

Here is one manufacture I found using google.
http://variac.com/staco_3pn10_20.htm

Scroll down the page to Portable Voltage Doublers - 120V input/0-280V output.

http://www.iseincstore.com/3pn2520b-xdamvariabletransformer120vacsinglephaseinput0-280vacoutput43acasedmodelwithcordplugreceptaclelightedswitchandfu.aspx

Note the 250 volt output receptacle.
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Outlier,

For what the Joule Electra VZN-160 amps retailed for new I would buy the variac the manufacture recommends from the manufacture. From your last post there is a lot more going on than just varying the voltage to the amps. It sounds like the variac is built/mated specifically for the amps.

I would suggest when you get the new one keep a log on the hours used. Check the autotransformer winding wiper brush for wear and have it replaced long before it’s end of life.
I also hope your amps were not damaged when the variac started arcing.

Best of luck,
Jim

Outlier,

For what it's worth had the 120V branch circuit that feeds the variac been protected by an AFCI,(Arc Fault Circuit Interrupter), breaker the breaker would have tripped open when the variac started series arcing. I am just not sure if under normal operation of the variac a slight arcing of the wiper brush contacting the bared autotransformer coil as the variac was ramped up or down might cause the AFCI breaker to trip open.

You could have an electrician install an AFCI breaker in the electrical panel that feeds the branch circuit and find out when you get the new variac.

Note, depending how old the electrical panel is and manufacture of will determine if the electrical panel manufactured breaker will fit the model/style/series of your panel.

AFCI breakers have been in use since 1999. As per the 2014 NEC code all newly installed 120V 15 and 20 amp branch circuits used for lighting and receptacles in habitable areas of a residential dwelling unit shall be AFCI protected. It should be said the AHJ, (Authority Having Jurisdiction), has the final say where they must be used.

http://www.afcisafety.org/qa.html
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