Diy high voltage probe

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Sarmad suseyn
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Diy high voltage probe

Post by Sarmad suseyn »

Hi
I built hv probe 1000:1 can measure up to 40 kv
Easy to make . Im attaching circuit diagram. With printable pcb board .
Adjastable resistor for calibration.
You need :
80 10m resistor
1 820k resistor
1 33k resistor
1 50k variable resistor.
1000 volt on the meter 1 volt.
On the pictures with voltmeter with and without the circuit.
Good luck
Ps. Don't forget to make housing for it. A pipe for example and sink it in epoxy or paraffin. Just expose the variable resistor for calibration.
Attachments
high voltage.pdf
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ready high.pdf
(95.97 KiB) Downloaded 447 times
20200920_213252.jpg
20200920_212656.jpg
20200920_212444.jpg
20200920_212346.jpg
111937_11mg.jpg
111937_10mg.jpg
John Futter
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Re: Diy high voltage probe

Post by John Futter »

Sarmad
Well done I see from the resistors you have used that it is good for 24,000volts with no safety margin ie most small resistors are rated @ 300 volts
If you had used VR37 resistors you would have had a theoretical maximum of 280,000 volts
I do remember the Silicon chip article as I subscribe to that magazine
Sarmad suseyn
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Re: Diy high voltage probe

Post by Sarmad suseyn »

Dear John
I think those resistors can hold 40k volts which is enough for me
And you are right about the VR37 resistors. They can hold more.
Check P.S i have told you have to sink it in epoxy or paraffin in pvc pipe
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Rich Feldman
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Re: Diy high voltage probe

Post by Rich Feldman »

Nice work there; thanks for demonstrating by doing.

It's OK to talk about using parts above their ratings. This is no worse than using MWO diodes to rectify a NST output, when operating PRV can be more than 21 kV.
Electrical component abuse is a popular theme on Tesla coil forums.
All are cases where component failure won't precipitate death and destruction.

An industrial maker, or user, can't validate a little resistor by applying 500 V and seeing that it doesn't arc over.
He can check for departure from Ohm's Law (an effect I found dramatic last year with carbon composition resistors).
Then check that the properties don't degrade after years of 500 V at rated operating temperature.
Hint: they do degrade, at least for some R values in the series. That's why 500 V resistors and VR37's are special and cost more.
All models are wrong; some models are useful. -- George Box
John Futter
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Re: Diy high voltage probe

Post by John Futter »

Sarmad
I knew you were putting the resistors away from air by potting oil. paraffin, epoxy
That is not the point it is the resistors themselves that cannot stand the voltage stress unless specially made for that use.
Rich has pointed out a couple of the possible failure mechanisms -there are more!
The VR37 series are quite cheap for what they do there are others that are just as good if not better.

My problem with what you have published is that someone will copy it with maybe even more inferior resistors and put themselves at risk from electric shock or at minimum pop an expensive digital multimeter for the sake of a couple of dollars difference in the cost of the resistors. Nowhere did you give the specification for the resistors you used and they look like ordinary 0.25 or 0.5 watt leaded ones.
Sorry I'm an aging Electrical Engineer with 43 years of experience in high voltage engineering--I'm just trying to keep readers safe
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Richard Hull
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Re: Diy high voltage probe

Post by Richard Hull »

Of course the quantity of resistors can make this make up capable of 20 watt or 40 watt dissapation handling easily a 1 ma current. the DVM will not demand a tiny fraction of 1 ma. The key factor is that at least 1/4 watt resistors would be needed for the 500 volts across each one at 40kv. Film resistors are a must. Carbon comps of yesteryear are far too likely to change values rather quickly under the stress. 500 volts will never arc over any resistor in the 1/4 watt size. 1 kilovolt will also not arc over such a clean resistor supported on its leads in air. I doubt is 2kv would arc over either.

The real issue is dust, corona and associated string value change, over time, which will naturally accumulate within such a string exposed, naked, to air. Oil dunking in pure, unscented, boiled mineral oil would obviate a lot of issues.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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