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Safely testing 22 kV capacitors
"Ignoramus27088" wrote in message
. .. The seller was wrong in describing them as 22 VOLT capacitors. They are 22 KILO volt capacitors. (the seller is Fermilab). This is kinda a sad commentary on the kind of people they'll hire at Fermilab these days, no? I don't know the proper care and feeding of such high energy storage capacitors, but when I've seen people working with them they always carried a long (about 6') wooden stick with a shorting strap (about 1"x6") on top to always ensure the caps were discharged before they touched them. |
Safely testing 22 kV capacitors
On Thu, 30 Mar 2006 19:52:44 GMT, Ignoramus27088 wrote:
The procedure would be - connect everything - put on hearing protection - turn on the franceformer - disconnect franceformer with remote disconnect. - turn face away, short the steel flats using broomhandle - hear BOOM - describe testing in the ebay ad Something in the dim recesses of my mind is telling me that a "boom" discharge would be bad for caps. I'd rather, as a buyer, see a one, five, and ten minute voltage check, and know that it was discharged through a power resistor. Those, I can help you with. |
Safely testing 22 kV capacitors
Last time I did a boom with a capacitor, it broke the "broomhandle" AND
the capacitor terminal leaving a nice leak hole... And that was ONLY 300V, but 10uF. I think the resistor way is safer. |
Safely testing 22 kV capacitors
OBones wrote:
Last time I did a boom with a capacitor, it broke the "broomhandle" AND the capacitor terminal leaving a nice leak hole... And that was ONLY 300V, but 10uF. I think the resistor way is safer. For some reason I'm not seeing the original post, so I'll tack this on here--if their condition is unknown it would be a good idea to have a solid barrier between you and the capactor when charging and discharging the first time, and do one at a time.. Also, have good ventilation in the test area--if one blows you probably don't want to breathe what comes out of it. -- --John to email, dial "usenet" and validate (was jclarke at eye bee em dot net) |
Safely testing 22 kV capacitors
Discharging caps that way can ruin the cap. Just turn off the supply or
apply a resistor load. The internal plates violently move - ripping themselves up. You get away with it - smile - sell it - it blows up when used. Not a happy day. Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member Ignoramus27088 wrote: On Thu, 30 Mar 2006 11:44:24 -0800, Joel Kolstad wrote: "Ignoramus27088" wrote in message m... The seller was wrong in describing them as 22 VOLT capacitors. They are 22 KILO volt capacitors. (the seller is Fermilab). This is kinda a sad commentary on the kind of people they'll hire at Fermilab these days, no? Indeed. I don't know the proper care and feeding of such high energy storage capacitors, but when I've seen people working with them they always carried a long (about 6') wooden stick with a shorting strap (about 1"x6") on top to always ensure the caps were discharged before they touched them. OK, I think that we are up to something here. The test setup that I may try is as follows: - 9kV franceformer feeding the cap, with remote disconnect leading to the HV pole - Wires from the cap connected to two junk steel flats, all set safely apart - A shorting stick (also made of junk steel) with a wooden broomhandle The procedure would be - connect everything - put on hearing protection - turn on the franceformer - disconnect franceformer with remote disconnect. - turn face away, short the steel flats using broomhandle - hear BOOM - describe testing in the ebay ad i ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Safely testing 22 kV capacitors
Ignoramus27088 wrote:
On Thu, 30 Mar 2006 11:44:24 -0800, Joel Kolstad wrote: "Ignoramus27088" wrote in message m... The seller was wrong in describing them as 22 VOLT capacitors. They are 22 KILO volt capacitors. (the seller is Fermilab). This is kinda a sad commentary on the kind of people they'll hire at Fermilab these days, no? Indeed. I don't know the proper care and feeding of such high energy storage capacitors, but when I've seen people working with them they always carried a long (about 6') wooden stick with a shorting strap (about 1"x6") on top to always ensure the caps were discharged before they touched them. OK, I think that we are up to something here. The test setup that I may try is as follows: - 9kV franceformer feeding the cap, with remote disconnect leading to the HV pole A FranceFormer is a neon sign transformer, and definitely AC. - Wires from the cap connected to two junk steel flats, all set safely apart - A shorting stick (also made of junk steel) with a wooden broomhandle Hmmm, better be sure that stick is dry, clean and free of cracks in the wood. The procedure would be - connect everything - put on hearing protection - turn on the franceformer - disconnect franceformer with remote disconnect. - turn face away, short the steel flats using broomhandle - hear BOOM - describe testing in the ebay ad The boom might be quite impressive, as these are probably Marx generator pulse discharge caps, and may have a current capacity of tens of thousands of amps. Jon |
Safely testing 22 kV capacitors
On Thu, 30 Mar 2006 21:26:26 -0600, Jon Elson wrote:
The boom might be quite impressive, as these are probably Marx generator pulse discharge caps, and may have a current capacity of tens of thousands of amps. Yes, they say "DISCHARGE CAPACITOR" on the dataplate. They probably were using them to power high power lasers. One of my acquaintainces worked there on lasers at some point. i |
Safely testing 22 kV capacitors
Ignoramus27088 wrote:
On Thu, 30 Mar 2006 23:01:22 +0200, OBones wrote: Last time I did a boom with a capacitor, it broke the "broomhandle" AND the capacitor terminal leaving a nice leak hole... And that was ONLY 300V, but 10uF. I think the resistor way is safer. ok... what would be a good resistor... I figure, 1 megohm or so should be just about right, RC of these 1 uF caps would be about 1 second. Discharging most of about 40 joules in a couple of seconds. i Well, let's see. P = 22 kV squared / 1E6 = 484 Watts. Well, that isn't so amazing, but I don't know where you will find a 1 Meg Ohm resistor with a 500 W rating and a 22 KV voltage rating. Jon |
Safely testing 22 kV capacitors
I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of
them in series, would that be sufficient to rectify 9,000 VAC safely? I have read some articles discussing that since leakage amps are not identical, that I need to put resistors in parallel with them. If so, these need to also be 1kV rated resistors, right? If not, would anyone have a suggestion for a 30 mA rectifier for 9 kVAC? thanks i |
Safely testing 22 kV capacitors
Ignoramus27088 wrote:
- A shorting stick (also made of junk steel) with a wooden broomhandle At the olde ion beam lab, we used pvc or fiberglass handles, not wood. Wood would be a poor choice. And a resistor (a big honking 50W resistor, which the Lab's EE assured inquiring minds WOULD NOT be surviving a full discharge - this is a safety tool used to approach supposedly discharged capacitors and be damn sure that they are discharged before you touch them, not a device to discharge them through, other than that last few hundred volts which is more than enough to kill you...) Speaking of which, you never want to store these things without having them shorted, solidly. A HV capacitor which is just sitting around can collect a lethal mount of static. If they did not come to you pre-shorted, someone was not behaving responsibly at fermilab. It's been a few decades, so I don't recall the precise size of the banks involved, but even the little bitty ones made a bang of unholy proportions, and spewed a fine dose of X-rays around the discharge area as well. Nobody but nobody got anywhere near the things when they were charged, and they lived in tanks full of transformer oil to keep the terminals from arcing over in the air. The big one (many capacitors) sounded a bit like dropping a V-8 engine from 3 stories, and vaporized the electrodes every time it was fired. If the capacitors are oil-filled, and they probably are, you need to verify (or make the seller verify) that they are free of PCBs, or you are in for a world of trouble disposing of them in any way. They should not have sold them if they were, but you need to be sure. In short, you really do not want to test these to anywhere near their capacity. Your HV supply is not suitable, and if it was, you'd be looking at a world of hurt without investing a few thousand in test gear. You could test them in a low-voltage RC circuit, I suppose, but for all actual purposes which they might be used, it's not very relevant. -- Cats, coffee, chocolate...vices to live by |
Safely testing 22 kV capacitors
On Fri, 31 Mar 2006 04:02:07 GMT, Ecnerwal wrote:
Ignoramus27088 wrote: - A shorting stick (also made of junk steel) with a wooden broomhandle At the olde ion beam lab, we used pvc or fiberglass handles, not wood. Wood would be a poor choice. And a resistor (a big honking 50W resistor, which the Lab's EE assured inquiring minds WOULD NOT be surviving a full discharge - this is a safety tool used to approach supposedly discharged capacitors and be damn sure that they are discharged before you touch them, not a device to discharge them through, other than that last few hundred volts which is more than enough to kill you...) Speaking of which, you never want to store these things without having them shorted, solidly. A HV capacitor which is just sitting around can collect a lethal mount of static. If they did not come to you pre-shorted, someone was not behaving responsibly at fermilab. Thank you. I will pick them up on Tuesday early morning, I believe that they are all shorted. Well, here's a picture of the data plate, courteously emailed to me by the seller: http://igor.chudov.com/tmp/cap.jpg Do you thikn that it has PCBs? In short, you really do not want to test these to anywhere near their capacity. Your HV supply is not suitable, and if it was, you'd be looking at a world of hurt without investing a few thousand in test gear. You could test them in a low-voltage RC circuit, I suppose, but for all actual purposes which they might be used, it's not very relevant. Thanks... I will think about this... i |
Safely testing 22 kV capacitors
According to Ignoramus6399 :
Well, here's a picture of the data plate, courteously emailed to me by the seller: http://igor.chudov.com/tmp/cap.jpg Maxwell Labs caps are really nice quality pulse discharge capacitors. Do you thikn that it has PCBs? Hmm ... It says "impregnant MIPB" which sounds like something different from PCBs. You might check whether they are still in business, and ask them. And these *might* actually surivive a dead-short discharge -- but it is still kinder to them to not do that. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
Safely testing 22 kV capacitors
Ignoramus6399 wrote:
I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of them in series, would that be sufficient to rectify 9,000 VAC safely? I have read some articles discussing that since leakage amps are not identical, that I need to put resistors in parallel with them. If so, these need to also be 1kV rated resistors, right? If not, would anyone have a suggestion for a 30 mA rectifier for 9 kVAC? According to http://www.pupman.com/listarchives/1.../msg00143.html "Use a MOT diode: typically they are 9kV 450mA and very cheap." Apparently MOT means microwave oven transformer. Note, the 9kV RMS AC of your Franceformer presumably peaks at about 13kV, so you would need a variac on its input if using a single 9 kV diode. Also see http://www.pupman.com/listarchives/1.../msg00309.html in same thread, which implies that obvious tubes like 1B3 won't handle 30 mA. -jiw |
Safely testing 22 kV capacitors
"Ignoramus6399" wrote in message
... I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of them in series, would that be sufficient to rectify 9,000 VAC safely? Nah- 9kVAC is 12.7kV peak, call it 15kV peak. The rectifier has to stand off full voltage on the backswing, so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) If you make a doubler (which uses diodes of the same rating, but produces twice the output voltage) you can test the capacitors at a bit over rated voltage (maybe 26kVDC, 118% of ratings). All the caps I've bought are rated for 150 or 200% of rated voltage for some time, though that doesn't mean these are. If you bring up the voltage slowly, through a resistor or variac perhaps, you can monitor it (assuming you get a voltage probe) and stop right at 22kV or so. I have read some articles discussing that since leakage amps are not identical, that I need to put resistors in parallel with them. If so, these need to also be 1kV rated resistors, right? Yeah, but conversely, I recall reading an article which stated that modern diodes are avalanche rated, meaning that if the voltage across one diode increases to say, rated PIV, current starts going up (it looks like a really high voltage zener diode), pulling it back into balance. Capacitors across the diodes were also recommended, but today's diodes are more rugged to pulse and avalanche conditions (we've come a long way from "top hat" diodes!) so this isn't necessary either. If not, would anyone have a suggestion for a 30 mA rectifier for 9 kVAC? Could rip the diodes out of a few TV sets/monitors. Or use the flybacks themselves, LOL. Tim -- Deep Fryer: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
Safely testing 22 kV capacitors
On Fri, 31 Mar 2006 00:33:12 -0600, Tim Williams wrote:
"Ignoramus6399" wrote in message ... I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of them in series, would that be sufficient to rectify 9,000 VAC safely? Nah- 9kVAC is 12.7kV peak, call it 15kV peak. The rectifier has to stand off full voltage on the backswing, so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? I have read some articles discussing that since leakage amps are not identical, that I need to put resistors in parallel with them. If so, these need to also be 1kV rated resistors, right? Yeah, but conversely, I recall reading an article which stated that modern diodes are avalanche rated, meaning that if the voltage across one diode increases to say, rated PIV, current starts going up (it looks like a really high voltage zener diode), pulling it back into balance. Yes, tat would be very nice. i |
Safely testing 22 kV capacitors
"Ignoramus27098" wrote in message
... so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? 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: http://webpages.charter.net/dawill/tmoranwms |
Safely testing 22 kV capacitors
On Fri, 31 Mar 2006 09:44:00 -0600, Tim Williams wrote:
"Ignoramus27098" wrote in message ... so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? 30-50kV PIV "diode", collectively. You can make that "diode" out of as many 1N4001 diode*s* as you need. :) 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 |
Safely testing 22 kV capacitors
Martin H. Eastburn wrote:
Discharging caps that way can ruin the cap. Just turn off the supply or apply a resistor load. The internal plates violently move - ripping themselves up. 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. |
Safely testing 22 kV capacitors
In article ,
Ignoramus6399 wrote: Do you thikn that it has PCBs? 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. -- Cats, coffee, chocolate...vices to live by |
Safely testing 22 kV capacitors
Ignoramus27098 wrote:
On Fri, 31 Mar 2006 09:44:00 -0600, Tim Williams wrote: "Ignoramus27098" wrote in message ... so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? 30-50kV PIV "diode", collectively. You can make that "diode" out of as many 1N4001 diode*s* as you need. :) 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 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. |
Safely testing 22 kV capacitors
On Fri, 31 Mar 2006 18:53:25 GMT, Rich256 wrote:
Ignoramus27098 wrote: On Fri, 31 Mar 2006 09:44:00 -0600, Tim Williams wrote: "Ignoramus27098" wrote in message ... so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? 30-50kV PIV "diode", collectively. You can make that "diode" out of as many 1N4001 diode*s* as you need. :) 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 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 |
Safely testing 22 kV capacitors
On Fri, 31 Mar 2006 19:05:12 GMT, Ignoramus27098 wrote:
On Fri, 31 Mar 2006 18:53:25 GMT, Rich256 wrote: 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? Well, first thing you need is a big capacitor... |
Safely testing 22 kV capacitors
Ignoramus27098 wrote:
On Fri, 31 Mar 2006 18:53:25 GMT, Rich256 wrote: Ignoramus27098 wrote: On Fri, 31 Mar 2006 09:44:00 -0600, Tim Williams wrote: "Ignoramus27098" wrote in message ... so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? 30-50kV PIV "diode", collectively. You can make that "diode" out of as many 1N4001 diode*s* as you need. :) 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 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 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. |
Safely testing 22 kV capacitors
Rich256 wrote:
Ignoramus27098 wrote: On Fri, 31 Mar 2006 18:53:25 GMT, Rich256 wrote: Ignoramus27098 wrote: On Fri, 31 Mar 2006 09:44:00 -0600, Tim Williams wrote: "Ignoramus27098" wrote in message ... so you need 30kV diodes, minimum. 40 or 50kV would be even nicer. ;) 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? 30-50kV PIV "diode", collectively. You can make that "diode" out of as many 1N4001 diode*s* as you need. :) 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 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 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. |
Safely testing 22 kV capacitors
According to Ignoramus27098 :
[ ... ] 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. 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. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
Safely testing 22 kV capacitors
"Jim Stewart" wrote in message ... Martin H. Eastburn wrote: Discharging caps that way can ruin the cap. Just turn off the supply or apply a resistor load. The internal plates violently move - ripping themselves up. 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. 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. |
Safely testing 22 kV capacitors
Iggy, does that transformer output alternating current or direct current? --Winston |
Safely testing 22 kV capacitors
On Sat, 01 Apr 2006 13:08:16 -0800, Winston wrote:
Iggy, does that transformer output alternating current or direct current? AC, as it turns out. i |
Safely testing 22 kV capacitors
DoN. Nichols wrote:
Do you thikn that it has PCBs? Hmm ... It says "impregnant MIPB" which sounds like something different from PCBs. You might check whether they are still in business, and ask them. http://www.gaep.com/frequently-asked-questions.html IPB, IPBP, MIPB = isopropyl biphenyl MIPB is mono-isopropyl-biphenyl Might be current stuff. Google can turn up more... Thomas |
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