High Voltage Probes

[eccerr0r]

Curious who owns a high voltage probe anymore these days... has it gone obsolete along with CRTs?

Unfortunately I don't have one, but I was wondering about how to measure high voltages and realized all my multimeters topped out at 1000V and some even less than that...except for one...

My Eico 555 analog has a 5KV range (and 100M ohm input impedance).

Next highest is my VTVM at 1.5KV. Then my Viz DMM at 1.2KV (AC, 2KV DC).

My Fluke and Mastech are 1KV and the rest go downhill from there.

I was thinking about making a resistor divider circuit to be able to measure CRT voltages but decided against it and just infer voltages... not worth building something that' may not be very safe and get by ones own jury rigged tools...

[xelectech]

Re: High Voltage Probes

Curious who owns a high voltage probe anymore these days... has it gone obsolete along with CRTs?

Unfortunately I don't have one, but I was wondering about how to measure high voltages and realized all my multimeters topped out at 1000V and some even less than that...except for one...

My Eico 555 analog has a 5KV range (and 100M ohm input impedance).

Next highest is my VTVM at 1.5KV. Then my Viz DMM at 1.2KV (AC, 2KV DC).

My Fluke and Mastech are 1KV and the rest go downhill from there.

I was thinking about making a resistor divider circuit to be able to measure CRT voltages but decided against it and just infer voltages... not worth building something that' may not be very safe and get by ones own jury rigged tools...

I made a HV-probe back in the 80's, the local electronics store had some HV resistors for real reasonable (can't remember how much, but well under 10 bucks), the rest of the parts'
cost were neglible, scrounged out of junk. Don't need it for TVs anymore, but still have used it to check things like a microwave oven or an electrostatic paint system.

I once used a dmm to check the output of a HID lamp ballast, that was supposed to be
8 or 9 hundred volts, that was the end of that meter's useful life, even though it was supposed to be good for 1000V. I can't really say how much the probe is good for but I used it regularly working on crts, probably at a max of 35Kv, was matched to 10Mohms input impedance. You could easily build one, if you could find one of those resistors (10Mohm replacement for HV probe), but I'd guess they're ridiculously expensive these days, though I haven't checked.

I'll attach a pic...

[Per Hansson]

Re: High Voltage Probes

This might be interesting if you want to build one:
https://www.youtube.com/watch?v=jUvSP3BQpvs

But then again some makes nowdays are really cheap, here is one rated for 28kV at under €100
https://www.elfa.se/en/high-voltage-...-40/p/17609540

[stj]

Re: High Voltage Probes

i could exeed that, i need a cheap one that goes to atleast 35Kv
27Kv is the running voltage of some industrial 26inch crt's

[Per Hansson]

Re: High Voltage Probes

I see it handles AC up to 28kV (at 300Hz max) but DC up to 40kV

[eccerr0r]

Re: High Voltage Probes

I've got a few 10Mohm resistors, alas hope the wattage is sufficient for voltage, and would need to make sure they don't arc over. Ouch.

Also kind of funny is that my meters are all over the place in terms of input impedance. My VTVM, Fluke, and B+K are 11M ohm input, though most of my other "10Mohm" input meters are actually 10Mohm (one is actually 9M ohm). I guess this matters when the HV probe assumes the meter to be of a certain input impedance else we'll need to do some math... However for CRT voltages, probably being off 10% probably isn't a big deal.

[budm]

Re: High Voltage Probes

I've got a few 10Mohm resistors, alas hope the wattage is sufficient for voltage, and would need to make sure they don't arc over. Ouch.

Also kind of funny is that my meters are all over the place in terms of input impedance. My VTVM, Fluke, and B+K are 11M ohm input, though most of my other "10Mohm" input meters are actually 10Mohm (one is actually 9M ohm). I guess this matters when the HV probe assumes the meter to be of a certain input impedance else we'll need to do some math... However for CRT voltages, probably being off 10% probably isn't a big deal.

You need to check the breakdown Voltage of your resistors, most regular resistor has 250~500V rating so to handle something in 10 of thousands of Voltage you will need to string up a bunch of resistor or get high Voltage rating resistors.
I.E.:
http://www.high-voltage-resistors.co...s-and-dividers

[xelectech]

Re: High Voltage Probes

I've got a few 10Mohm resistors, alas hope the wattage is sufficient for voltage, and would need to make sure they don't arc over. Ouch.

Also kind of funny is that my meters are all over the place in terms of input impedance. My VTVM, Fluke, and B+K are 11M ohm input, though most of my other "10Mohm" input meters are actually 10Mohm (one is actually 9M ohm). I guess this matters when the HV probe assumes the meter to be of a certain input impedance else we'll need to do some math... However for CRT voltages, probably being off 10% probably isn't a big deal.

I was trying to recall exactly what is in my probe, it's just 2 resistors, I think the high voltage one must be 1000 megohms, its about 4 or 5 inches long and has a hole in either end where a screw goes for attaching a wire, the other resistor is just a normal 1/2 watt 1 megohm one, which the voltage is picked off of, so I guess that makes its input impedance 1 megohm. I wrote down a correction factor that accounts for different input impedances: if R=impedance of the meter, then (1.11 + R) divided by (1.11 X R) is the multiplier to correct for different input impedances. Don't remember where I got that info, but I wrote it on the probe and clear-coated over it.

So, it's a thousand to one voltage divider, but is assembled in such a way that I'd probably have to break it to get it apart and confirm it's contents, except for the 1 meg resistor, I can confirm that with my meter. I don't know why I was thinking it is 'matched'
for 10 megohms input impedance, been too many years since I made it...