VARIAC....MEX?

That'll work just fine. These units have an easy-access glass fuse (AGC?) to protect them just in case a boo-boo happens. To make the switch last longer I always tweak the dial down to zero before throwing. Same for shutoff. I posted a link to a neat set of AC gauges, it would be neat to measure incoming voltage and total amperage when using it with a genset.

Hi mena,

Lots of capacity on that one for the purpose you want it for.

If you want a better one, Staco or Superior Electric (Powerstat) are almost bullet proof.

Hi,

Many variacs say to not turn the dial with a load on it. I would not be turning the load down to 0 volts before shutting it off. Rather I would shut off the charger first, then with no load you can adjust the voltage.

I had been thinking of using a 10 amp variac to recharge a electric car project I have been thinking about. I would be recharging a 72 volt battery bank, and use the variac to control the input voltage to a home built rectifier.

2 amps at 110 volts is about 220 watts, while the charger input is around 150 watts with output being 10 amps at 13.4 volts. So you should have about 30% more capacity than the charger input. Yet be careful that nobody puts the charger on "Start" mode, even for a little while, that mode will have about 20 amps output at 15 volts or so, more than 300 watts output, so much more than 320 - 330 watts input. Still not enough to trip a 3 amp fuse on the Variac, so be careful.

Hi Fred,

It is good to know that the dial should not be moved when there is a load on.

The unit referenced is rated at 500 VA. Give the battery charger 0.7 for power factor. 500 X 0.7 = 350 watts. Plenty for the 10 amp setting and enough for 20 amps. (20 x 12 = 240 / 0.7 = 343 watts)

westend wrote:
If you want a better one, Staco or Superior Electric (Powerstat) are almost bullet proof.

I've had this one since high school 40+ years ago. She's still grindin' along, just a tad light tho.

pianotuna wrote:
Hi Fred,

It is good to know that the dial should not be moved when there is a load on.

The unit referenced is rated at 500 VA. Give the battery charger 0.7 for power factor. 500 X 0.7 = 350 watts. Plenty for the 10 amp setting and enough for 20 amps. (20 x 12 = 240 / 0.7 = 343 watts)

Thanks for doing the math PT, Golden had me sweating for a moment. So I'll need to turn off the load BEFORE turning the dial?? Hmmm. I was hoping I could adjust the VARIAC while the charger was on to keep the output steady or to slow the rise. Turning it on and off seems like a PITA although I guess I would know where to turn the dial to after messing with it.

I have an old 6 amp charger that is nothing more than a transformer and diode. I installed a small variac within the charger case decades ago. I can adjust it to charge any voltage battery up to 12 volt and any current from zero to 6 amps. I have had no issues adjusting it while under load.

Golden_HVAC wrote:

"Many variacs say to not turn the dial with a load on it. I would not be turning the load down to 0 volts before shutting it off. Rather I would shut off the charger first, then with no load you can adjust the voltage."

I have used hundreds of variacs over the last 40 years or so. Used to control many kW of power. Most of the equipment needed to start at zero volts and slowly brought up to operating voltage. Shutting down was also a slow reduction of voltage. Some equipment had motor driven variacs that automatically adjusted the voltage, always under load. I don't ever remember a variac spec that said not to adjust under load. It would be interesting to see such a spec.

The manufacturer doesn't want the transformer field to collapse. I've started out a zero and went to 50% capacity so many times I lost track at the thousand mark.

But no, the dial should not be "spun". Incrementally increasing or decreasing voltage has never posed a problem for me AS LONG AS THE UNIT IS NOT LOADED MORE THAN 80% capacity. I have had too many loaded variac switches fail when flipped.

So starting at 0 then modulating the dial upward to where you want it isn't a problem as long as it isn't horsed. Same for decrease. When Mena posted his question I calibrated the % load by the charger and it does not approach saturation level of the toroid. Twisting from 0 to 65 volts should take longer than 10 seconds.