High Voltage breakdown tester

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Maciek Szymanski
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High Voltage breakdown tester

Post by Maciek Szymanski » Fri Oct 16, 2020 8:02 pm

I’ve bought cheaply an old HV breakdown tester. I haven’t tracked the wiring diagram yet, but it looks quite simple - a variac, an iron core transformer and a bunch of ballast resistors (primary side) and simple relay control circuits plus digital voltmeter. I’ve bought it mainly for this nice panel controlled variac but does anyone have some experience with this kind of animal? What are those HV transformer characteristics? Surely not usable for fusor - I don’t know exact voltage rating but probably mere 5kV. But it looks like a 100mA (suppose time limited) so it should be able to make some nice plasma.
I think I have seen something like this in some movie torture scene...


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Richard Hull
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Re: High Voltage breakdown tester

Post by Richard Hull » Fri Oct 16, 2020 11:27 pm

We see impulse HV testers at our scrap yard here on occasion. A weak one is 30kv I have one that goes to 80KV. Un-fortunately, the one we get are designed to supply no more than a few hundred micro amps before they trip out due to punch through arcing. I think you might find it a lot higher voltage than 5kv. Let us know. That variac and transformer look like they can handle some power....More than microamps.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Maciek Szymanski
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Re: High Voltage breakdown tester

Post by Maciek Szymanski » Sun Oct 18, 2020 3:38 pm

I’ve disassembled and tracked the circuit. Even if it’s simple the tracking was not so easy because the cables are not marked and use only few colors. Also part of the Control circuit is not used - maybe it’s intended for some kind of proof testing the unit itself.
Primary side can be switched between three ballast resistance sets: four 270Ω resistors in parallel(67Ω total), 4,7Ω or 2,2Ω. The panel switch is marked 10, 50 and 100mA output. I asume output voltage as 5kV as the insulated test probes are rated 6kV. Interesting feature of the transformer is that it has a separate winding for voltage measurement to which the panel meter is connected. The variac has a mysterious 4th terminal to which the power indicator led is connected. Maybe it’s a fixed low voltage tap - I’ve to do the measurements yet.


The control board with ballast resistors. It’s amazing that there are total 4 relays each one of different type.
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Last edited by Maciek Szymanski on Mon Oct 19, 2020 10:02 am, edited 2 times in total.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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Dennis P Brown
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Re: High Voltage breakdown tester

Post by Dennis P Brown » Mon Oct 19, 2020 10:00 am

Wow, no integrated circuits! That is certainly an 'old school' electronics' device. Should be fairly straight forward to trace and fun.

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