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Old 04-16-2012, 09:32 PM   #1
Mukai
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Question What is a variac?

A co-worker was telling me he uses an old variac to slow a box fan down in his den. What is a variac?
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Old 04-16-2012, 09:36 PM   #2
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Default Re: What is a variac?

It's a variable transformer. Most allow you to go from about 0 to 140 VAC. It kind of looks like a giant potentiometer.
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Old 04-16-2012, 09:38 PM   #3
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Default Re: What is a variac?

Variac is the trade name for an autotransformer.

Basically it lets you change the output voltage. Some are adjustable and others have "taps" at preset levels.
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Old 04-16-2012, 10:09 PM   #4
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Default Re: What is a variac?

Wow, I haven't seen a Variac in 30+ years.
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Old 04-16-2012, 10:16 PM   #5
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Default Re: What is a variac?

We still have them at work. We use old stuff if it still works well, and variacs work very well. We use them to reduce power to electric heaters for thermal tests.

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Old 04-16-2012, 10:20 PM   #6
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Default Re: What is a variac?

Quote:
Originally Posted by thammel View Post
We still have them at work. We use old stuff if it still works well, and variacs work very well.
Honestly, I'm not even sure what the modern replacement is for high amperage portable testing.
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Old 04-16-2012, 11:05 PM   #7
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Default Re: What is a variac?

They also have the benifit of acting as an isolation transformer.
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Old 04-16-2012, 11:05 PM   #8
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Default Re: What is a variac?

The Variac is high on my thriftshop hunting list. I haven't seen one yet, but I know I will and it will be mine. Also high on that list is an Ohmega 2-channel strip chart recorder...
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Old 04-17-2012, 07:56 AM   #9
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Default Re: What is a variac?

I bought one at a garage sell for $2, its a 30 amp model, large dial like from the 50's. I use it to slow down my old router.
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Old 04-17-2012, 08:27 AM   #10
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Default Re: What is a variac?

If you like rock music, Eddie Van Halen used a variac to reduce the voltage to his Marshall amplifier so he could crank the amp's output while keeping the overall volume lower. It allowed him to get a lot of gain (sensitivity) while keeping his sound from being too trebly...i.e. his "brown sound". It sort of changed rock and roll!
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Old 04-17-2012, 08:46 AM   #11
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Default Re: What is a variac?

> Also high on that list is an Ohmega 2-channel strip chart recorder...
Wow, good luck on that hunt!
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Old 04-17-2012, 10:53 AM   #12
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Default Re: What is a variac?

Quote:
Originally Posted by ForceFed70 View Post
They also have the benifit of acting as an isolation transformer.
Wrong - they are an AUTOTRANSFORMER - no isolation from the AC line.
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Old 04-21-2012, 01:33 PM   #13
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Default Re: What is a variac?

That is correct. An Variac offer no isolation.
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Old 04-21-2012, 04:31 PM   #14
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Default Re: What is a variac?

Got about 10 of them in the barn. They were used for the dv-22 surgical lights for intensity control. Go up to 180 vac, handy to have. Search for Amsco dv-22 intensity controls. I'm sure they are still out there. Heavy suckers though.
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Old 04-21-2012, 09:39 PM   #15
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Default Re: What is a variac?

I have 2 of them
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Old 04-21-2012, 09:48 PM   #16
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Default Re: What is a variac?

If you search over on http://homedistiller.org/forum/ they go over it in GREAT detail.

They use them to build heater controllers to control their boilers.
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Old 04-22-2012, 02:58 AM   #17
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Default Re: What is a variac?

Quote:
Originally Posted by Roots View Post
Honestly, I'm not even sure what the modern replacement is for high amperage portable testing.
The modern replacement would be the VFD.

Quote:
Originally Posted by Falcon67 View Post
> Also high on that list is an Ohmega 2-channel strip chart recorder...
Wow, good luck on that hunt!
Hmmmm...I should see if we still have those 2 old 1 channel Honeywell circular chart recorders laying around....one of them even had an I/P.
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