I got this
Fluke 80K - 40 kV High Voltage Probe for free in a broken and dead state and since I have to take it apart anyways for the repair attempt, I thought to document the repair here.
Problems:
- 999 Mega Ohm resistor is broken at the end
- 1 Mega Ohm resistor seems to be dead (Open)
- Cable broken (and far too stiff)
- dual banana plug broken
- High Voltage tip broken.
First, I need to find a way to attach the 999 MOhm resistor to the front tip again.
Very nice! I have a RCA probe like this. Clean the 999M resistor before putting it back in. Your fingerprints are basically HV short circuits.
Solder the same points together carefully, and exacly in the center. I used some epoxy to bond them together, as the solder connection broke quite fast when I turned the tip back on.
If it is impossible to repair the resistor: You can easily get 1G resistors rated at up to 50kV.
Solder the same points together carefully, and exacly in the center. I used some epoxy to bond them together, as the solder connection broke quite fast when I turned the tip back on.
This resistor tip/metal must be some kind of stainless steel because no solder is sticking to it.
Even right in the center, I can not get any solder to flow.
So, I think I will solve this problem very differently.
I drilled a 2.6 mm hole in to the metal adapter of the tip and inserted an Ingun spring loaded test-pin.
This should work great, as far as it looks now.
I just have to build a ring guide for the resistor out of PTFE (Teflon) so it will stay in the center of the probe.
After you have repaired this, how are you going to convince yourself that it is safe to use (for instruments and yourself)?
What tests will you do?
After you have repaired this, how are you going to convince yourself that it is safe to use (for instruments and yourself)?
What tests will you do?
It's a fluke probe, i have the same one. The only thing that really protects you or a device is the single 1G resistor and the ground connection. I guess fluke has confidence in this part. It is over 10 cm long. flash over is unlikely at 40kvdc. But still, just one resistor.
After you have repaired this, how are you going to convince yourself that it is safe to use (for instruments and yourself)?
What tests will you do?
First I will keep the ground clip installed, which will have a good ground connection up to the handle and where the 1 MOhm resistor is grounded.
Installing new cables will help a lot for safety, since the old one is partially broken
May be I will test the tube for high voltage leakage but I am not convinced that this is needed.
Since I have to build a a guide for the resistor anyways, I might build a Teflon tube, to add some additional level of safety.
You have any further ideas?
Well, I just tested the 999 MOhm resistor with my Keithley 2450 SMU
With 100V source voltage, the resistance is measured kind of stable to 994.6 MOhm
So, I will assume that the main resistor is working well.
Just be safe when you use it.
I measured the output voltage of a 100kva 15kv transformer with it.
Turn all power off, hook on the probe and set the dmm to the right setting.
Turn power on, read the measurement but don't touch the meter or the probe.
Power off before changing dmm settings. This way nothing can go wrong really when the resistor fails. just the dmm.
Mine was in perfect nick. But still ,a single resistor even by fluke is not a good enough protection for me between a serious hv supply and me.
Whilst I have a lot of respect for 20kV, an interesting comment inside my old Tek 545, warned that the "low voltage" supplies (150-500v DC) were more dangerous than the HV - as the HV could only supply few mA, whereas the 'LV' supplies could supply almost an amp.
I have a "chicken pedal', an idea I heard from EEVblog forum, its a foot switch which powers all the devices under test, lift your foot off and it switches the power off.
However I agree with ArjanEmm, if at all possible, don't touch and work with another fellow standing by.
Ok, I am kind of happy with my outcome so far
I made some Teflon spacers that fit perfectly in to the original Fluke tube
Then I cleaned the 999 MOhm resistor with some alcohol
and made another spacer to have a positive force against the new spring loaded connector.
Actually, I think this is how Fluke should have done the probe to begin with.
And then I installed a new cable
This is a high quality, very flexible "MultiContact, MC" cable with silicone jacket.
The new ground cable is also a silicone insulated cable.
OK, all is together now and ready for testing.
Ok, tested and passed for up to 5 kV
It seems to be very accurate as well.
1 kV show: 1.001 V
2 kV show: 2.020 V
5 kV show: 5.053 V
Now I have to build a jig to test for up to 40 kV
I'd be wary of those nylon spacers, as they change the distribution of the fields inside the tube, potentially creating gaps of air with a high
density of field lines which will result in sparkovers
Actually, I think this is how Fluke should have done the probe to begin with.
Have you considered that Fluke chose
not to do that for some good reason?
I suspect there are many subtle and infrequent failure mechanisms in HV kit, and that specific design features are there for a good reason. Long-term contamination and deposits spring to mind.
With HV you have this thing called surface tracking. Where air meets the insulator surface, the break down voltage is actually lower than air it self.
This is one of the reasons hv insulators have complicated shapes. To create more length over that surface.
100kvdc will just bridge a 10 cm air sparkgap, but will easily spark over a 30 cm sheet of hdpe for example.
Thanks for all the feedback
I have an older HP high voltage probe and the main resistor was housed inside a teflon tubing, before it was inserted in to the housing of the probe.
The hole inside my PTFE spacers are a little larger than the resistor and the resistor surface is not touching the spacer.
I am now testing at 10 kV DC and everything is working great so far.
Will see how it looks, when we reach higher voltages.
@HighVoltage - while there Amy be some additional paths for surface contamination with the teflon spacers, I would imagine the extra support on the high value resistor ( and poss reduced micro fracturing from bumps etc) may overall be beneficial.
@MasterTech - great idea - sorry I couldn't give you credit by name - dementia onset!
I have a newer design to offer
The newer design uses ceramic substrate and film resister (I guess). The one I got has the tip base/holder detached from the pad, cold joint I suppose. I tried to re-solder it. I know it’s mostly likely a silver pad on ceramic, I also have 2% silver solder from Goot. But this is the first time I work on ceramic, and silver solder cooled down slower than I expected, too long and overheated the pad :’(.
Lesson learned:
Lower soldering temperature, I read somewhere around 300°C
Tip on component lead, not on the pad
Secure your component to avoid movement during plastic range
Fast in, fast out
Now I must find some silver epoxy to fix it. Hopefully the silver under the mask is still good and intact.
Ps
https://groups.io/g/TekScopes/message/144610?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3ACreated%2C%2CSilver+epoxy%2C20%2C2%2C0%2C12123998“ I suspect that if you did a really good job of cleaning the ceramic, you could replace the silver with a silver epoxy paint made for electronics work. I have successfully soldered
to such paint in the past. “
-Chuck Harris
Yes, the new version of the FLUKE80K probe also uses ceramic chip resistors inside.
I have the same one as your picture
Thank you HV. May I know if yours from MG is solderable?
I'm trying a silver adhesive from China, it seems working, 0.1~0.2 Ω when use as bridge between pads, cured on hot plate. But seem not solderable onto.
Thank you HV. May I know if yours from MG is solderable?
I'm trying a silver adhesive from China, it seems working, 0.1~0.2 Ω when use as bridge between pads, cured on hot plate. But seem not solderable onto.
No, this is not solderable.
And no need for it.
0.1~0.2 Ω will have no effect on measurements.
Just use the conductive epoxy and it will work well, I am sure.
I don't think silver paint should be used.Use a knife to scrape off the place where the pad falls, use fine welding, pull out the copper needle and fix it with green insulating oil.
