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Ben Solon

Mon Feb 25 2013, 03:03AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Back again.

I'm looking to buy a variac, but I don't want to spend a lot on it. For general usage and tesla coiling, what power level should I be looking at? The 20 amps look nice, and they'll take anything my wall can dish out, but they cost a pretty penny. What do all of you use? If I got a 10 amp would I be able to do short runs with it pulling higher power? Any suggestions? I know I can get a good deal on ebay, but how much should a 10A or a 20A cost?

thanks

Physics Junkie

Mon Feb 25 2013, 04:23AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

I just bought a 10A 140VAC Powerstat on ebay for 40 bucks. I'm using it for tesla coils. It should come in the mail this week so if you want more info I can let you know how it works. But to answer your question, for general usage 10A is fine and you should be able to get a good deal on ebay for less then $100. 20A would work but just consider the power level of the stuff you're going to be using it for and cost. 20A will be $100+ at least for the ones I've seen.

Ben Solon

Mon Feb 25 2013, 04:58AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

The problem is that for testing my mid-sized drsstc(a good 2 kw) I'd be concerned with burning it up. A 10A might hold for 30 seconds or so, but after that all bets are off :) I can spend 100 on one just fine, I just don't want to be spending 300 or so on one piece of equipment unless its just that necessary.

Houdini0118

Mon Feb 25 2013, 10:46AM

Registered Member #8558 Joined: Thu Dec 06 2012, 11:38PM
Location: usa
Posts: 57

i have a 10A one i got for free and i quite like it but one thing to remember is even a 20A one WILL NOT TAKE WHAT EVER THE WALL CAN DISH OUT. Its a transformer so if you run it at 12v you cannot pull 2kw through it. I would not recomment running them over their power limit to much or replacing the fuse with a bolt etc. It might work but it also might shorten the life of the variac.

Steve Conner

Mon Feb 25 2013, 10:54AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Exactly, the limiting factor is the current that the brush can stand. It's a good idea to put a fuse or breaker in series with the brush.

Ben Solon

Mon Feb 25 2013, 03:15PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Houdini0118 wrote ...

i have a 10A one i got for free and i quite like it but one thing to remember is even a 20A one WILL NOT TAKE WHAT EVER THE WALL CAN DISH OUT. Its a transformer so if you run it at 12v you cannot pull 2kw through it. I would not recomment running them over their power limit to much or replacing the fuse with a bolt etc. It might work but it also might shorten the life of the variac.

What I mean by that is that running a tc at full line voltage, the breaker will trip before the variac will go up in flames.

Thomas W

Mon Feb 25 2013, 03:30PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

try finding a ham fest near you and chat with EVERYONE, i was chatting with a guy there and thats how i managed to get a large 40-50A variac for $25

HV Enthusiast

Mon Feb 25 2013, 03:43PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

A variac can be pushed to about 2x its rated current for short periods of time (not continuous), however, you should still properly fuse it as in a fault condition, you could weld the brushes to the core and create a dimple spot.

IamSmooth

Wed Feb 27 2013, 03:06AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I think it is a good investment if you are serious about electronic experiments to buy a fused high current variac. You will always use it, and you won't have to fear that it will fry. I have a 10A fused one for general purpose development.

GrantX

Wed Feb 27 2013, 06:05AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

I am also currently in the market for a larger variac. I own a tiny little 2A, 0-260V model, which is perfect for small scale work, but I do find it a bit limiting. Occasionally I run it up to 3A intermittently (currently have a 5A fuse installed), but only with a clamp meter and a low-current breaker, so that I have appropriate sized protection and constant monitoring.

RS components have a 28A variac on their website, but it's about $1100, so I'm trying to find something second hand.

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