VARIACS

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
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bwsparxz
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Joined: Fri Aug 16, 2002 11:03 am
Real name: Brian Willard

VARIACS

Post by bwsparxz » Sat Jun 03, 2006 12:18 am

Most of you use large > 20 - 30 A variacs for your XRT's. I was curious if was possible to use a large inductive ballast and a small variac , 10A, to control a XRT or potential trannie? If not , does anyone have a spare 20 - 30 A available.

DaveC
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Re: VARIACS

Post by DaveC » Sat Jun 03, 2006 1:09 am

Brian -

You can certainly use a smaller variac than 30 Amps to control the XRT's primary voltage. What the primary current is, depends on the XRT turns ratio and the secondary current being drawn. If your variac is fused properly, all that can happen, if the input current exceeds the variac rating, is the fuse blows. The current limiting inductor will tend to turn the XRT into a large version of a Neon Sign Transformer. You will have a nice high open circuit voltage, but as the current increases, the inductor will begin dropping more and more of the primary voltage, and thus the secondary (HV) output will fall off.

With some careful attention to settings, you probably don't need the inductor and can use the variac to feed the XRT.

Just be careful, though. A 10 amp primary current at 120V is 1.2 kVA and that's a serious output, whatever the actual output voltage turns out to be. Way more than you need to make toast of yourself.

Dave Cooper.

bwsparxz
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Real name: Brian Willard

Re: VARIACS

Post by bwsparxz » Sat Jun 03, 2006 10:13 am

I see. So do others just use larger one for overhead? Right now I only have (1) 10 A and don't want to toast it. Richard used to have all different sizes, but I am not sure if he sold them already. Also, the 60 Kohm ballast resistor on the HV side limits the secondary current.

UG!
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Re: VARIACS

Post by UG! » Sat Jun 03, 2006 3:03 pm

varacs are very tough due to the large iron core. if you point a few fans at them you can a) use them that at a higher current that they are rated for (at least on the short term) and b) tell when there getting hot by the smell :)

unless you are planning to activate your entire neighbourhood, i would say 10A would be fine :) i'm useing a 10A one to control the power to the huge 5Kv PSU on my website, and have never managed to make it warm.

Oliver

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