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4hv.org :: Forums :: General Science and Electronics
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variac used for higher voltage

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Patrick
Mon Dec 13 2010, 02:05PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
so we all agree that if you take a Variac way above its normal Vac, that it burns to the ground right?
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ubuntupokemoninc
Mon Dec 13 2010, 02:26PM
ubuntupokemoninc Banned on 1/22/2011 for repeated rule violations after multiple warnings.
Registered Member #3299 Joined: Sat Oct 09 2010, 08:11PM
Location: Bantown, USA
Posts: 220
if you ballast the variac, at the same kva thats its rated for i can't imagine any harm comming to the core, i think 35 amps wouldn't do it any good, best go with 25 because its half of 50, i get old variacs out of 3 phase welders, but there only rated for like 500va.
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Proud Mary
Mon Dec 13 2010, 02:40PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
It will be very quickly destroyed if a fuse doesn't blow first. A silly waste!
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Muttyfutty!
Mon Dec 13 2010, 06:28PM
Muttyfutty! Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
hmm... is it possible to wire a Variac in reverse. so, to get a higher voltage?
Or is insulation a problem as you go above 230V?
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Dr. Slack
Mon Dec 13 2010, 07:07PM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
hmm... is it possible to wire a Variac in reverse. so, to get a higher voltage?

To get to a higher voltage an your are inputting to it, yes. To get to a higher voltage than is on the nameplate, no.

Take a 240v input variac, turn it down to give 24v output. Now unplug it, and drive the output from a 24v transformer, and something like 240v will appear on the input terminals.

Try turning the varaic "up" from here. You increase the number of turns that you are driving from your 24v input, so the core flux decreases and the voltage generated on the input terminals goes down.

Try turning the variac "down". You decrease the number of turns, and so for a small variation, the core flux goes up and the voltage genertated rises. Encouraged you turn a bit more, core flux increases to saturation and you start pulling big current. The voltage on the input terminals never goes much above 240v because the flux hasn't increased much.
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radiotech
Mon Dec 13 2010, 08:35PM
radiotech Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
A vatiac is just an autotransformer. Autotransformers are
the most efficient way of using steel and copper. Unfortunately
they are very difficult to protect and have tricky behaviours
which requires a roomfull of electricians and mathmaticians
to gather in "network analysers"

Perhaps someone will invent a better automatic way of doing
this in the futur.


1292272502 2463 FT103140 Acnetwork
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