Variac Current rating.

[ziggy007]

Hi Guys,
In the market for a Variac. Have some how managed to get by without one but have a current (pun intended) job that I need one to stop frying fuses.
What current rating do you guys recommend. There seems a lot with a 2A but that seems a bit low ball to me.
Just thought Id ask those more knowlegable than my self.
Cheers
Gav

[nosaj]

Hi Guys,
In the market for a Variac. Have some how managed to get by without one but have a current (pun intended) job that I need one to stop frying fuses.
What current rating do you guys recommend. There seems a lot with a 2A but that seems a bit low ball to me.
Just thought Id ask those more knowlegable than my self.
Cheers
Gav

I myself prefer the dim bulb tester http://www.geek-tips.com/2015/11/22/dim-bulb-tester/
nosaj

[Leo_Gnardo]

Australia is 220-240V AC supply, right? 2 amps is kind of marginal. I say splash for a variac with 5 amps rating. And you can use a combination of variac plus light bulb limiter if you have both. That may come in handy for testing solid state amp gear.

[Enzo]

I have a 1kW variac, it has served me well for 50 years. It is fused at 8A on 120v. On 240v that would be about 4A. So I have to agree with Leo, 5A is a reasonable level.

I agree with nosaj that a bulb limiter is simple and cheap and will stop bl;owing fuses. But I also see that as a differnt piece of gear than a variac. I cannot "ramp up" a bulb limiter. And I watch the mains current on a meter with my variac, such readings are not very meaningful with a bulb.

If I work on a 3000 watt power amp, my 1kW variac is overloaded at that level. But when using a variac, I never power a amplifier to its full power, I am generally working on an amp at idle, in which case the variac is perfectly happy.

[ziggy007]

Ta guys, grabbing a 5A one today. Cheers

[Jazz P Bass]

" I need one to stop frying fuses."

If this is truly your goal, then a variac is not a cure by itself.
It would be best to hook up a current meter to the unit.
And a current limiting device.

[The Dude]

Agree. If you can find a variac with a built in current meter, you'd be ahead of the game. Otherwise, I'd put one inline when you are firing something up for the first time.

[Leo_Gnardo]

Agree. If you can find a variac with a built in current meter, you'd be ahead of the game. Otherwise, I'd put one inline when you are firing something up for the first time.

This ^^^ or my variation: I use a clamp on ammeter, no clip leads needed, no chance of popping a fuse in a regular meter.

[ziggy007]

The clip on current meter is a great idea.

[Enzo]

In any case, a variac without a current meter is only half an instrument.

[nevetslab]

For general bench work, a 10A rating, or a 1KVA rating would be a good choice. The cost difference isn't that much different between a 5A rating and a 10A rating. Superior Electric has made excellent 10A rated variacs, and can be strapped internally to go from either 0-120V or 0-140V. I'd steer away from the Chinese imports, even though they look cool and have a meter, I wouldn't trust one. A friend of mine was asking me about buying one, and I see they have held their high prices just as they did 40 years ago. Might look in pawn shops or swap meets for one, or even garage sales it it looks like there's shop gear visible.

I've always used external meters with my variacs. You can find Weston AC Voltage and AC Ammeters available for not outrageous prices. Valhalla 2101's do fetch a bit of $$, but well worth it, owning a couple myself. They have greater than 20kHz BW, and can also be used to measure TRUE Amplifier Output Power when not being used for AC mains monitoring.

[Enzo]

Even if a variac had a meter on it, I too prefer a separate meter. I have a unit similar to this I use a lot:

https://www.ebay.com/p/Robinair-Volt...1478061&chn=ps

The large meters are easy to see, and my variac can stay off to the side, and I don't have to crane my neck to see it.


I occasionally pick up another variac at the university surplus facility nearby. Much cheaper than new. They generally have quality stuff like SUperior rather than Chinese.

[ziggy007]

Man, I just gotta move to the states. You guys are seriously spoilt for choice!

[DrGonz78]

You know I got this General Radio variac w/ ammeter for $175 back in 2012. With shipping I paid $200. But the money spent was all profit money that I made selling a really nice Polytone amp on eBay.

It looks similar to this one but this one toggles between 2A and 10A and mine is only 1A and 5A. I love this thing and it is built to last. I know I could have gotten a similar setup for less money but honestly it was worth the extra bucks. Now I see these going on eBay from $500-650 and that is outrageous!! To me I would pay $150-200 on one of these but not more than that. Mine is similar to General Radio meter below.
https://www.ebay.com/itm/VERY-GOOD-S...bdc8%7Ciid%3A1

The red painted chinese variacs have issues. For one, they are covered in red paint and the ground lugs are usually not making contact with the chassis of the unit. So you would need to take the unit apart and modify the unit to have dependable connections.

[Helmholtz]

I use a cheap plug-in energy monitor like this:

https://www.conrad.com/ce/de/product...requenz-LCD-00

It is quite accurate and gives me voltage, current, apparent and real power (especially useful to determine PT losses), cosphi and more.