Supplier for 15kV/250nF or similar pulse caps - Page 1
Forum section: electronics / projects

author: daqq
author_rank: Super Contributor
timestamp: October 27, 2015, 11:24:30 am
content: Hi guys,For a project we need caps with a total capacity of 250nF @15kV. They must be able to provide a short pulse of around 15Amps pulse, with a duty cycle of 0.1%. Any ideas on where to start looking? It must be a normal supplier, not ebay NOS.Thanks,David

author: Marco
author_rank: Super Contributor
timestamp: October 27, 2015, 11:36:09 am
content: Just from hanging around on a laser mailing list the following names come to mind, Maxwell, Aerovox, General Atomics.PS. given your location Russian suppliers might have some nearby distributors as well, but no idea where to start looking for them.Googleis always a good start though

author: TerraHertz
author_rank: Super Contributor
timestamp: October 27, 2015, 11:43:51 am
content: http://www.highenergycorp.com/High Energy Corp. | PO Box 308 | Lower Valley Road | Parkesburg, PA 19365 | phone: 610-593-2800The HV ceramic disk caps from Nitto Denji (Japan) are probably all too low in capacitance. Hard to tell since their site doesn't seem to have an English version.Gosh, googling "high voltage pulse capacitors" turns up some pics of spectacular looking gear.

author: Marco
author_rank: Super Contributor
timestamp: October 27, 2015, 01:53:53 pm
content: Forget what I said, you don't really need a pulse capacitor. Those are hopelessly overspecced for your relatively low current pulses.

author: Arjan Emm
author_rank: Regular Contributor
timestamp: October 27, 2015, 04:14:06 pm
content: Pulse caps are rated in the kA ranges. Way too heavy duty.Maybe a couple of IGBT snubber caps in series? I know WIMA has 3kVdc 2,2uF ones. 5 in series might be close enough. They are probably overrated too, current wise.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 27, 2015, 07:52:25 pm
content: Snubber caps I don't think come high enough in value, but DC link (bypass) caps should do. They come up to 875 or 1100V, something like that. Maybe 20 in series, so values of 5uF, which are easily found.Tim

author: daqq
author_rank: Super Contributor
timestamp: October 27, 2015, 09:21:34 pm
content: Hi guys,First of all, thanks for the information. The reason for the pulse caps was that this should be quite fast - very low rise time ( <100ns preferable) and the actual on time should be around 2us, with a repetition rate of 500Hz - this gives a fairly low average power, but a large pulse power. As such parasitic inductances could cause problems. The best parameters I've seen were in various pulse caps.The reason for the relatively high capacitance is that the voltage should drop as little as possible during the actual pulse.But now that I think about it you are right, a bank made up of a series-parallel combination of good fast (but not too pulsy) caps should do the trick, assuming some charge balancing resistors are used.Is there any cap you would recommend for this? I'll scour the obvious suspects (EPCOS, ES-OSTRAVA, AVX) tomorrow.Thanks,David

author: Marco
author_rank: Super Contributor
timestamp: October 27, 2015, 10:34:06 pm
content: Maxwell will gladly sell you something for 1000s of dollars which will undoubtedly do what you want.I'd just get something likethisand try it out (pretty sure that's a CJE capacitor by the way).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 27, 2015, 10:59:48 pm
content: Stray inductance isn't a concern. 15kV and 15A is an impedance around 1kohm, so you're looking at a time constant below t = L/R = 100ns, or L < 100uH.Tim

author: daqq
author_rank: Super Contributor
timestamp: October 28, 2015, 08:49:17 am
content: Thanks. Stray inductance is also a bit of a concern due to what happens after a quick change of current - you can get massive voltage spikes.

author: ElectronicTonic
author_rank: Contributor
timestamp: October 28, 2015, 03:38:58 pm
content: I used polypropylene pulse caps for my DRSS Tesla coil in series-parallel combination. Bought them from here:http://easternvoltageresearch.com/flexibrute_capacitors.html.They are also available from Digi-Key, Allied Electronics, etc. The biggest cap in the series is 0.15 uF, 2000V, Conell-Dubilier 942C20P15K-F. It has 5 m-ohm ESR, 32 nH ESL, 2879 V/us dV/dt, 432 Amp peak current.I used the 0.10 uF caps in combination to get 0.025 uF, 24 kV. Here they are in my Tesla coil if you're interested:https://www.youtube.com/watch?v=HdwcZX07NFk&list=PLmj4qMKo6w6dj18EPKZKn10BVotjBsFHY&index=1.Skip to 8:17 to see the caps.Hope this helps.

author: LaserSteve
author_rank: Super Contributor
timestamp: October 28, 2015, 04:01:11 pm
content: Quote from: Marco on October 27, 2015, 11:36:09 am