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Old 12th September 2011, 11:40 AM   #1
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Default Too big variac, and 3 phase

I asked a friend if he could get me a big variac for a nice price. He knew what I needed it for, so I assumed he would find a ~1000VA one.

Since I got it for free, I couldnŽt turn it down. Even tho I wish I had when I went to pick it up. Its really really heavy.

The problem is that its 3phase, and I have no idea on how to convert or use it on single phase here at home.
If I just connect ground and two of the three hot wires, will it work?
I know im only getting 2x0-220 instead of 3x0-220, it dont matter.

The goal is to get X-0-X output, e.g 26-0-26 so I can test a chipamp.
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Old 12th September 2011, 11:58 AM   #2
AndrewT is offline AndrewT  Scotland
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Just insulate the inputs to the two phases you don't need.
Connect to the remaining Phase and Neutral, just as you would do for single phase Live and Neutral.

Ground, or Earth, or PE are quite separate. None of these are Neutral.

But, ask an electrician to check what voltage it is designed for use with. It could be 220Vac or 400Vac for each phase.

I think you could wire up one or both of the spare phases to give a second and/or third "in-phase" output/s. Again the electrician should be able to confirm.
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Old 12th September 2011, 12:09 PM   #3
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If you use it for a chip amp which u can do using your variac, BEWARE that it is not isolated and touching even 26Volts will be lethal.

Gajanan Phadte
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Old 12th September 2011, 12:16 PM   #4
AndrewT is offline AndrewT  Scotland
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I think I can see lots of transformers inside, along with the 3 Variacs.
It will be very easy to measure/check if any outputs are not isolated from the mains.
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Old 12th September 2011, 12:56 PM   #5
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Live and neutral. Got it.

Come to think of it, I have to connect at least one more fase for X-0-X output.

The correct ting would be....? tie the two live wires together? Tying the live and N together sounds very wrong :P

There are 3 large transformers (20cm/8" diameter) and one a tad smaller for the DC outputs.
The large ones have to be for isolation, right? What else reason is there for putting an extra 45kg of Cu inside?

Besides.. voltages below 50v dont scare me very much. To much resistance in our body, so IŽll take my chances with the chip amp.
The Perreaux on the other hand... 80-0-80v makes for a nasty rail voltage.
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Old 12th September 2011, 06:23 PM   #6
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What you've got there actually contains THREE variacs. (I'm well familiar with the configuration, though not that particular piece of equipment).

Take it apart and you will find three cores. May take some dissasembly as they are linked together in a carrier and threaded through with a motorized rotor unit.

After taking apart any one core may be connected to your mains as a normal single phase unit.

I envy you, thats a nice stack!

Doc
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Old 12th September 2011, 06:38 PM   #7
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Quote:
Originally Posted by thaumaturge View Post
What you've got there actually contains THREE variacs. (I'm well familiar with the configuration, though not that particular piece of equipment).

Take it apart and you will find three cores. May take some dissasembly as they are linked together in a carrier and threaded through with a motorized rotor unit.

After taking apart any one core may be connected to your mains as a normal single phase unit.

I envy you, thats a nice stack!

Doc
So there is no way I can get 2xAC from it without hooking it up to 3phase?
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Old 12th September 2011, 06:48 PM   #8
mpuman is offline mpuman  United States
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Too bad you are not closer! I'd make you a trade. Before you ASSUME anything, get a diagram or make one from the hardware.

My guess, like most variacs, it is not isolated. Can't really tell by the pix. Before you hook anything up - make sure that you fully understand the device, have a proper diagram, AND meter it out!

Good luck and SAFE - more people die with house current then all others put together.
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Old 12th September 2011, 06:48 PM   #9
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Quote:
Originally Posted by Forman313 View Post
So there is no way I can get 2xAC from it without hooking it up to 3phase?
Uh, sure. Take some circuit tracing though. Assuming you wish to use it as a standard type variac? If so then try to find which core has control circuitry paralelled to it. (Drive motor likely tapped off only one phase... that's the one you want.)


But reading back on your goals, the unit you've got is WAY overkill. Even so, if you've got it and it's yours to tear into it will certainly accomplish your goals.

To attain a 52V center tap (26..0..26) you may not even need to do any winding, dependingon existing taps on the cores. I myself have made a very nice amplifier power supply by just splitting existing windings with a dremel wafer and then deviding the new issolated secondary into the voltages I needed. Cores like in the unit you've got there typically have multiple taps spaced around them.

I'll help to whatever level I'm able to.
Doc



Doc
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Last edited by thaumaturge; 12th September 2011 at 07:02 PM.
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Old 12th September 2011, 07:27 PM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
Just insulate the inputs to the two phases you don't need.
Connect to the remaining Phase and Neutral, just as you would do for single phase Live and Neutral..
Quote:
Originally Posted by Forman313 View Post
Live and neutral. Got it........
...............The correct ting would be....? tie the two live wires together? Tying the live and N together sounds very wrong
insulate is not the same as tying the live & N together.
If you can't translate english back into something you can understand correctly then you are on the wrong Forum.
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