ziggy007 7/26/2018 7:27 PM
Variac Current rating.
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 7/26/2018 7:40 PM
Quote Originally Posted by ziggy007 View Post
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 7/26/2018 8:01 PM
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 7/26/2018 8:23 PM
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 7/27/2018 6:43 AM
Ta guys, grabbing a 5A one today. Cheers
 
Jazz P Bass 7/27/2018 11:40 AM
" 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 7/27/2018 6:20 PM
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 7/27/2018 6:24 PM
Quote Originally Posted by The Dude View Post
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 7/27/2018 6:44 PM
The clip on current meter is a great idea.
 
Enzo 7/27/2018 6:49 PM
In any case, a variac without a current meter is only half an instrument.
 
nevetslab 7/27/2018 11:53 PM
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 7/28/2018 12:17 AM
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 7/28/2018 12:27 AM
Man, I just gotta move to the states. You guys are seriously spoilt for choice!
 
DrGonz78 7/28/2018 12:45 AM
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 7/28/2018 8:19 AM
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.
 
Enzo 7/28/2018 9:21 AM
Over here we have the similar Kill-A-Watt. Not expensive at all. Useful tool.
 
nosaj 7/28/2018 9:56 AM
Quote Originally Posted by ziggy007 View Post
Man, I just gotta move to the states. You guys are seriously spoilt for choice!
Check your local ham clubs That's where a lot of good quality stuff can come from. I'd even imagine where you are too. Make friends with the hams let them know what you do and more often than not they are more than willing to help and provide a very fair deal when they know you won't flip it.
nosaj
 
olddawg 7/28/2018 10:31 AM
I always used one of these:
https://rover.ebay.com/rover/0/0/0?m...2F223044211989
The AC leakage test was required by law in CA. We added $2 for the test and put a signed sticker on the unit. Paid for the variac over time.. The meter displayed line voltage, output voltage, current, leakage to chassis, etc. I used to hook it to a bridge rectifier and a 4700uf cap to make an adjustable DC supply as well that would tell me the current draw.
 
Tom Phillips 7/28/2018 10:35 AM
The energy monitors give you a lot of information for the price. However, for test bench use, I want analog meters! There is a lot a value is seeing the true rate of change of the voltage and current as you ramp up the voltage. One can even see pulsing of the current flow which would be obscured by the sampling rate of the inexpensive digital device. I always power the amp under test through the variable transformer. That allows me to know the exact line voltage appled to the amp and to set a standard test value so that my readings are not affected
 
Helmholtz 7/28/2018 11:15 AM
Quote Originally Posted by Tom Phillips View Post
The energy monitors give you a lot of information for the price. However, for test bench use, I want analog meters! There is a lot a value is seeing the true rate of change of the voltage and current as you ramp up the voltage. One can even see pulsing of the current flow which would be obscured by the sampling rate of the inexpensive digital device. I always power the amp under test through the variable transformer. That allows me to know the exact line voltage appled to the amp and to set a standard test value so that my readings are not affected
True, I have and use both at times. No problem to wire the digital power meter and an analog ammeter in series. The issue is that analog meters mostly are of a certain age and often develop a hysteresis caused by mechanical friction in the instrument's bearing. Thus, for accuracy I prefer digital meters.
 
Tom Phillips 7/28/2018 1:13 PM
Quote Originally Posted by Helmholtz View Post
... The issue is that analog meters mostly are of a certain age and often develop a hysteresis caused by mechanical friction in the instrument's bearing...
I have seen that issue on some old meters. Especially those that were used on standard consumer equipment or medium to lower price test equipment of the day. However, the good quality analog leaders of the day just seem to go on forever giving excellent performance. Unfortunately those high-quality movements can be hard for the average person find. When you have good ones at your disposal they are a joy to use.
 
Helmholtz 7/28/2018 1:35 PM
Quote Originally Posted by Tom Phillips View Post
I have seen that issue on some old meters. Especially those that were used on standard consumer equipment or medium to lower price test equipment of the day. However, the good quality analog leaders of the day just seem to go on forever giving excellent performance. Unfortunately those high-quality movements can be hard for the average person find. When you have good ones at your disposal they are a joy to use.
I was speaking of premium grade professional analog meters. I have a nice collection of those. Fine, if yours don't show the issue.