High Voltage Probe

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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Nicolas Krause
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High Voltage Probe

Post by Nicolas Krause »

I'm hoping to get one or two more projects done before classes start up again. Over fall reading break I threw together a pcb in KiCad for a high voltage probe. It's nothing too complicated, just the usual string of resistors but I put in the order to digikey for the parts today. Due to the awkward size of the board I ended up using a chinese board house to produce the pcb. That means I've got about 10 copies of the board lying around. I might put them up for sale if there's any interest (10$ each + shipping is what I was thinking). I'll start soldering once the parts arrive and then I'm planning on putting it in a piece of pvc tubing filled with parafin wax to improve safety.
IMG_1467[1].JPG
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Nicolas Krause
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Re: High Voltage Probe

Post by Nicolas Krause »

Components arrived this morning, and after a whole whack of soldering I've placed nearly all the resistors, might make some cosmetic adjustments to position in a bit, but the bulk of the soldering work is done!
IMG_1470[1].JPG
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Bob Reite
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Re: High Voltage Probe

Post by Bob Reite »

Is that a series parallel arrangement? Or all in series with a zig zag?

To replace my 600 meg resistor that went bad, I opted to buy 6 Vishay/Dale 100 megohm resistors model ROX-2 that are intended for high voltage use.
Hopefully you don't have trouble with corona at the top end of your series string.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Nicolas Krause
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Re: High Voltage Probe

Post by Nicolas Krause »

It's all in series with a zig zag. I'm using VR37 resistors with the exception of the tuning potentiometer and a single 30kohm resistor at the very end of the chain
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Nicolas Krause
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Re: High Voltage Probe

Post by Nicolas Krause »

I've used the most recent bit of spare time to complete the High Voltage probe. I mounted the PCB inside some plastic piping and filled the tube with paraffin wax for insulation. A nail was driven through one end of a cap and then connected to the board via a soldered wire.
IMG_1650.JPG
IMG_1651.JPG
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Dennis P Brown
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Re: High Voltage Probe

Post by Dennis P Brown »

Extremely professional and well thought out 'high voltage' probe! Your approach is very clever and execution so clean. Your skills, like many here, are extraordinaire.

I some-what cheated on my HV 'build'; I bought a dirt cheap HV probe that didn't work. It had a simple but calibrated micro-amp meter in its base marked in kV (0-45.) Turns out its high voltage resistor was broken (about seven inches long and 1.1 giga-ohm.) I bought a cheap Chinese 1.1 giga-ohm resistor (hardily calibrated but no way to test it. So I have to trust, and not verify ... .) This resistor was only six inches in length so I added an extension inside. I did test the probe against a somewhat accurate 10 kV supply and it agreed well. So, I assume its ok to its limit of 45 kV. I had to reverse the leads to the meter to get a proper negative reading probe.
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Richard Hull
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Re: High Voltage Probe

Post by Richard Hull »

I was fortunate enough to find a 0-40kvdc @ 2ma, 1R high, brand new, rack mount, Spellman supply in box at a teslathon some years ago with a nice digital meter on it. It is my calibration standard for HV meter assembly and testing. I used it often back when I was custom making metering systems for fusioneers. Gave it up as I figured I made about $10.00/hr doing it. Image attached.

Richard Hull
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Calibrating one of the many metering systems I made and sold way back when...
Calibrating one of the many metering systems I made and sold way back when...
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nicolas Krause
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Re: High Voltage Probe

Post by Nicolas Krause »

Thank you for the kind comments Dennis, at some point I might carve a bit of plastic out of an end cap to seal off the back end of the tube, but for now I'm going to leave it as is. Fascinating photo of the calibration Richard, at some point I'll have to do something similar on my end, no clue how to go about it at the moment!
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