Safely testing 22 kV capacitors

Hm... Were you trying to rectify a 60 Hz sinewave?

i

Well, first thing you need is a big capacitor...

>

Of course you can!! Do you have a piece of plexiglass about 15"-18" long, maybe 1"-1.5" wide? Just put 100X 1M resistors in series, and pick off

1/100 of the voltage at the bottom resistor. Silicone them down in sort of a zig-zag, solder the leads one to the next, trim them - leave a round solder glob at each junction to cut down on corona, and slather silicone all over the top and around the assembly.

Use a very high-impedance, input-protected voltmeter, like a VTVM ;-)

Good Luck! Rich

Both rectifying 400 Hz and use as a series diode in a resonant charging circuit. Actually I was using 1 ampere silicon rectifiers which were not fast enough. All it takes is one not turning off fast enough.

I don't remember just what we ended up using. I think it was about .001u and 10 Meg across each diode.

Another problem was that a few diodes had bad junctions and couldn't take the current. When you put 30 of them in series the probability of getting a bad one is pretty high. Had to weed them out first.

I guess my powers of observation are failing me Roy, but I always like to check out where I missed something and try and figure out why it escaped me.

Would you kindly point out where the OP revealed that he realized a HV probe would serve as a safe discharging means, albeit a rather slow one? (Before I mentioned it that is.)

Thanks,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat \'57 EE)

"Truth exists; only falsehood has to be invented."

Live and learn. I was remembering the ones I played with years ago which IIRC put out more like 20 ua, but I do agree that even that much current would make for an uncomfortably long wait.

I remember having to test the radiation hardness of some satellite equipment I designed. We went to a GE facility in Pennsylvania where they had a "flash x-ray" generator.

It used a BMF horizontally oriented Van De Graf IIRC about 25 feet long and two feet in diameter which took many minutes of running to build up the requisite high voltage in a storage capacitor. The charge was flashed through an x-ray tube to produce a humungous blast of x-ray photons into my poor little circuits.

Thanks for the mammaries,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat \'57 EE)

"Truth exists; only falsehood has to be invented."

People are regularly killed off the filter caps in microwave ovens.

You need to get a collection of EEM catalogs. Back in the 1993 edition, the Victoreen pages in the Resistor section says that it's most likely a MAXI-MOX rated at 22.5 kV. Rated at 4.5 watts if it's a MOX-3-13, epoxy coated or 7.5 watts for a MOX-3-12 silicone coated.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Why not keep them and start trying to shink coins? http://205.243.100.155/frames/shrinkergallery.html

This site has been recently edited to take out most of the technical details. I suspect it was a bit too dangerous for the average user.

Ignoramus27088 wrote:

According to Ignoramus27098 :

[ ... ]

You can make 30KV from a single 1KV 60 HZ transformer, with enough diodes and capacitors. The basic circuit of a voltage multiplier is:

(AC)---+--)|-+------+--)|--+-----(DC) | | | | \\---/ --- \\---/ --- \\ / / \\ \\ / / \\ --- /---\\ --- /---\\ | | | | (G)-)|--+-----+-)|---+------+

That one is enough for a 4X multiplication of the voltage. Keep adding pairs of diodes and capacitors and you keep adding voltage multiplications -- and losing current capacity.

1 KV AC is 1.414 KV DC peak, times 4 gives you 5.656 KV just with this simple circuit. At work, we used fairly small assemblies potted in epoxy to get 45 KV (three 15KV taps from a 1KV P-P input.

But -- it might take nearly forever to charge your caps.

Enjoy, DoN.

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You can't get more high-impedance than the electrostatic voltmeter which I posted a link to last night. (Probably the auction is closed by now.) But that kind of voltmeter would allow monitoring the voltage real-time until you decide that it is now time to discharge the capacitor.

Enjoy, DoN.

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Well, it's pretty hard to argue with that scenario.

I work at a similar facility and will have to see if they are doing the same sort of thing. Just the other day a Hardinge bed was sitting outside waiting for disposition of some sort. The stuff that gets thrown out there would make a die-hard scrounger cry, though most of it is probably entirely used up.

Mike

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On Fri, 31 Mar 2006 12:54:42 GMT, Ignoramus27098 Gave us:

Yeah. Those caps have a very limited number of pulse cycles where they are guaranteed to maintain their rated specs. After that they are typically swapped out of a system for new components. The old ones get used in the lab or get sold as a lot. That is very likely what those are.

Maybe Ignoramus is within his rights.

But Win has a very good point. In any event, if Ignoramus alienates Win and just a few other knowledgeable regulars here, his (Ignoramus's) experience will be badly degraded.

So he may want to think seriously about Win's protest.

--Mac

Thanks DoN. I think that I will just make a 13 kV charger with my 9 kV AC source and a diode.

i

What is worn out for some people, is treasure to other people...

i

Hm... So... DO you think that they are now useless, or simply a little out of spec?

i

I worked in a medical laser research group. We had 2u odd caps @ 10kv+ as part of a home brew laser supply. Before working on it we'd double check the caps were disharged in case the discharge resistors had failed.

A couple of PVC pipes 2m long with a 12" length of heavy neon sign cable linking them, a couple of M4 screws were stuck through the ends.

When the caps were charged it was like a gun going off - very sharp bang, it usually bought people out of offices all down the hallway. You never stood behind whoever had the rods in case you got a reacting elbow in the face.

r.