Safely testing 22 kV capacitors

Tim, I lost you a little bit here, sorry. Are you saying that I need single 30kV diodes and that putting 1 kV diodes in series is unsuitable? Or are you saying that twenty 1,000 V diodes is not enough?

Yes, tat would be very nice.

i

Yes, although I will probably keep one for myself.

Yes, you are right, it is indeed not easy. Thank you for your post, I saved it for future reference.

i

It's more likely that lab "junk" is sold off for salvage and that the salvagers or someone they've sold to are auctioning off the stuff. It seems really unlikely to me that anyone at Fermi Lab, or DOE for that matter, would bother to check Ebay seller names for usurpers of their "name". I haven't checked, but would guess that Fermi Lab's budget is at least a few hundred million dollars per year and technical staff probably bill out at around $125 and up per hour. They'd have to get pretty good prices for those caps at that rate to break even - did they?

Mike

It is, doubtless, definitely Fermilab. I will go to him on tuesday into Fermilab itself. I find it difficult to imagine a private individual sellings his own things in this manner.

i

[alt.marketing.online.ebay -- I am talking about an item that I won on ebay recently, see

Mike, I am going to Fermilab to pick up these capacitors on Tuesday and they want payment in form of checks made to Fermilab. They take my check on the spot and do not require it to clear. I would be greatly surprised if that was not a legitimate Fermilab operation.

I think that what we are observing is typical government/public funded surplus bullshit. I see the same stuff all over in military surplus. Everyone is going through the motions ("we are auctioning surplus to get highest competitive value"), but no one really cares to even understand what they are selling or what it costs to sell that stuff. Some things sell well for them (like high dollar electronic test equipment sold one piece at a time), some do not.

Now if this item was adequately described with love and care, then, I would suspect that it was not Fermilab but some private person who actually cares to get money for his stuff.

i

30-50kV PIV "diode", collectively. You can make that "diode" out of as many 1N4001 diode*s* as you need. :)

Tim

-- Deep Fryer: a very philosophical monk. Website:

News flash: the person doing the writing gets to decide how, or if, his work is distributed and stored. Demanding that he do it differently is no different than the people who ask a question and demand an email response. (equally stupid and arrogant, is the point I'm making).

Thanks, now I understand a little better. I will soon make a stack of, say, 30 1N4007 diodes. That would let me test the capacitors with 13 kV.

i

Dave, I sort of agree with both of you. I think that I have a right to hide my posts, but, on the other hand, I decided not to exercise it anymore. At least in this newsgroup.

i

Given that they were made by Maxwell and sold to Fermilab, they are probably spec'ed for pulse discharge. That said, I'd not want to be on the same city block when iggy crowbars them.

Putting a hard metalec short across them will no doubt blow half the terminal away, create a deafening blast and generate a nice EMP pulse. There's no way I'd do it.

Likely not, based on that label - it's simply something that, if you have ever had to deal with, you NEVER make assumptions about from that point on, because they were so widely used when they were in vogue.

Did something like that about 40 years ago. In our case we had to bridge each diode with a small capacitor and large resistance resistor because when seeing the reverse voltage, they did not all turn off fast enough.

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

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