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Identifying HV Pulse Caps

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LAN_403

mobilechernobyl

Thu Mar 26 2009, 03:08AM

Registered Member #2036 Joined: Fri Mar 20 2009, 04:08AM
Location: PA, USA
Posts: 3

Hello,

First post here, but have lurked for quite some time, defiantly a wealth of useful info here! I've been able to find just about everything I've been looking for either here on the Wiki, but with that said, I am at a dead stop on my latest project...

I am trying to find a pulse cap/caps to get a few uF at 5kV stored up, and released in a pulse under 5uS for wire exploding, and basically any type of food 'splodin. I will also be using this for a stepping stone into kV+ capacitor experimenting with can crushing and the like.

I've found quite a few caps on ebay that seem to be pulse discharge caps, but I am not sure if they are suitable for what I am trying to do (discharge them completely in under 5 uS).

here are some examples of what I've found,

2c36 1

and

both are Dearborn, CMLE series capacitors. they are about exactly what I'm looking for as far as storage capacity. They are paper in oil capacitors, and that is ALL the info listed on the ad. I can't find anymore info on them, but with my limited knowledge on identifying capacitors by how they look, the ceramic or glass insulators on top, coupled with the screw stud connections look good for being a pulse cap.

So if anyone can help me with information on this capacitors, that would be great. I am not looking for 100+ uF HV caps just yet, so don't tempt me, I'm just looking to start small with these 1uF caps and get into the HV cap experimenting game. Next phase will be designing, or copying a schematic for a charger. If anyone could help with that I would like it to charge off a 12v SLA battery, so any help there would be great as well!

Thanks, and awesome sight everyone!

Arcstarter

Thu Mar 26 2009, 03:23AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Hello, and welcome to the 4hv forum!

The first four caps all paralleled are 25 joules. That is not much, but i have used a huge capacitor charged to 25 joules at 2kv and i could shrink a can with about 4 hits, i exploded foil, and exploded little pieces of pickles. It was fun, then i charged to 4kv, which is 100 joules. This shrunk cans completely in 2 hits, and vaporized anything. I then charged to max voltage with my pole pig, which is 460 joules or something like that. I discharged it straight to the copper 'wire' (more like a rod) and it took a nice hunk out of it, while being earshattering loud (i put on ear protection after 25 joules). I tried charging it, but it was shorted. This took out my microwave high voltage diodes, another string of 1n4007's (not a major loss :P) and two 16000ohm 12 watt 'tunnel' resistors for my tube tesla coils. All from having .4-.5 amps through them at 7620 volts.

I say this alot, but i would use a ZVS :P. Mainly because there is such tiny heat, it can put out alot of power, they will NOT die if made right, and the simplicity (not to mention price). Wind your own transformer out of an old flyback transformer core. It works fine on 12 volts, and up to 40 volts with no modifications.

rp181

Thu Mar 26 2009, 03:24AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Its hard to tell.
On one side, they look like some other pulse capacitor's from general atomics energy products, but on the other, dearborn doesn't make any pulse capacitors. That combined with there old age, I wouldn't use them for pulse, at lest at there ratings. You should email that company, most have archives of data sheets, they could probably tell you its ratings.

Shaun

Thu Mar 26 2009, 03:43AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

I do not think these are pulse rated caps. The terminals look too small, plus paper+oil is not usually used for pulse caps as far as I know.

Also, I have some very similar caps (10kV 0.5uF) that are paper-oil with a metal can and similar terminals, which I know for a fact are DC blocking capacitors.

Hazmatt_(The Underdog)

Thu Mar 26 2009, 04:02AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

No, these are not pulse discharge caps, they are filter caps.

Download

Thu Mar 26 2009, 06:41AM

Registered Member #561 Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230

Paper caps are know to explode or burst when used in pulse roles, Go on eBay and search for "pulse capacitor".

Proud Mary

Thu Mar 26 2009, 09:02AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

They look like valve-era High Tension smoothing ('filter') capacitors to me.

You may not know that there has been quite a flurry of scientific and experimental interest in using aluminium electrolytics as pulse power devices.

Google 'electrolytic capacitor pulse power' and its variants, and you'll pull up all sorts of interesting factoids:

I doubt that even very low ESR electrolytics are as fast as you seem to require, but here, for future reference, is an abstract on their use:

Evaluation of electrolytic capacitors for high peak current pulse duty
Harris, K.W.; McDuff, G.; Burkes, T.R.
Electron Devices, IEEE Transactions on
Volume 38, Issue 4, Apr 1991 Pp: 758 - 766

"Summary: A new type of electrolytic capacitor has been developed specifically for high-peak-current applications. Preliminary results of an ongoing research effort to determine the operational characteristics of this new type of electrolytic capacitor are reported.

The new electrolytic capacitors, designed for pulse discharge application, were tested in a low-inductance discharge circuit to evaluate the maximum current extractable, internal inductance of the capacitors (equivalent series inductance), internal losses of the capacitor (equivalent series resistance), and the potential lifetimes of the capacitors.

The peak currents extracted ranged from 17 kA for the 2000-Î¼F unit to 27 kA for the 6800-Î¼F unit, with pulsewidths ranging from approximately 100 to 280 Î¼s for the 2000- and 6800-Î¼F units, respectively."

I've got a good number of large can low ESR bolt-ups - 15000uF/450V and the like - and may have a bash at it myself.

You can always dump the discharge into a Rayleigh pulse-forming line and shorten the pulse according to need, a technique for using electrolytics in pulse-power applications developed by the US Office of Naval Research. Anything is more attractive than massive steel tanks of dielectric oil with porcelain knobs on the top. Can't put that in a rocket, can you?

PS: Don't forget that pulse power capacitors have only a limited lifespan. As an extreme example, some very large Marx capacitors used in nuclear research often have Mean Time Between Failure rates of 100 shots or even less, despite their careful and costly design.

Try to use capacitors with current data sheets.

rp181

Thu Mar 26 2009, 03:08PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Do those 400v 15000uf capacitors you have happen to be EPCOS (I almost got 24 from them =( )? EPCOS has a whole line on pulse lyctics.

I would stay waway from using those as pulse. You might be able to try it, But if you do, have a nice strong enclosure. Pulse capacitors life times depens greatly on the ringback that is allowed. If you ever do get a pulse capacitor, be sure to design a circuit with minimal ringback.

Sulaiman

Thu Mar 26 2009, 06:13PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

The caps in the first post are almost certainly dc filter capacitors,
worse, since they were made before 1997 they probably contain PCB's
(polychlorinated biphenol) which are toxic and require disposal as toxic waste
(in Europe).

rp181

Thu Mar 26 2009, 07:10PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Good point about the PCB's. If newer capacitors explode, its not that big of a deal. If those explode, it will become a HUGE mess.
From your post, it sounds like you didn't buy any yet, thats good. Your best bet for low ringing 9coilgun, railgun) is lyctics. For can crushing and coil shrinking, try to find some pulse rated capacitors. You said that you didn't want to go high power quite yet, so it should not cost much.

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