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Registered Member #561
Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230
Got this variac pretty cheap, but no-one knows what sort of power rating it has, I’m pretty sure it must be over 15amps (at 240v), possibly into the 20amp range.
What I know: weighs about 20kgs, about 350mm across (not the frame), has the strange system where the brushes run along the side of the windings, instead of the top
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Strewth mate, looks like a bloody monster.
15-20A is probably about right. You can try loading it up and see how hot the brush gets. If you smell the brush burning, or see smoke coming from it, that's too much current!
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
Download:
1 - Carefully measure the tickness (diameter) of the winding wire, im milimeters. Lets say that you has measured the wire diameter as 2.5 mm 2 - Then calculate the wire cross section S as S=(pi/4) * d^2. S=(3.1416 /4) * 2.5*2.5 = 4.9 mm2 3 - If the wire is copper, the allowed current could be I= 3xS, or 3x4.9 = 14.7 amper, for continous operation service.
If the you will load on the variac 2 minuts and turn off for 8 minutes ( 20% working cycle ) you may use I=6xS or 6x4.9 = 29.4 amperes... Adding a fan , and keeping the 20% cycle, you may draw 8*S amperes ...
Anothe way to use all available amperes from the variac - Supposing that the insulation is class B, (up to 130C is allowed), one or two termistors placed inside the winding and conected with alarm in such way that the alarm rings when the temperature reach 130C. This will allow you draw more amperes without compromise the insulation or any part of the variac
Can you measure the winding wire with a caliper? An let us know the diameter ??
Registered Member #3700
Joined: Sat Feb 19 2011, 12:59PM
Location:
Posts: 107
Hi Dowload Hi Newton !
In addition to the Newton comments: Im suspecting that the variac is for 460V. Estimate on count how many turns are in the iron core, Measure the IRON CORE internal diameter, outside diameter and the high of the iron core. Calculate the iron core cross section. with this information we can verify if the windig is for 230, 380, 460V or other voltage.
I don't ahve any calipers on hand, but it would be over 2mm
I'm not sure more pics will help, there is nothing on it to identify it, no nameplate, seriel number, etc. The guy I bought this from had been using it with his valve amps
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Identifying a Variac
