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$10 2.1 uF 5kV electrolytic capacitors in pulse discharge, journal article claims.

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Superkuh

Fri Oct 17 2014, 01:18PM

Registered Member #59 Joined: Thu Feb 09 2006, 05:45AM
Location: Wisconsin, USA
Posts: 12

Palm top plasma focus device as a portable pulsed neutron source (pdf)
Low voltage operation of plasma focus (pdf)

I recently ran in to a series of journal articles published in the AIP Review of Scientific Instruments that feature some pretty surprising claims about electrolytic capacitors used in pulse discharge service. Each paper describes using 4x 2.1 uF 5kV electrolytic capacitors in parallel to make a ~8uF 5kV bank that reaches a peak amperage of 53kA with a pulse width of tens of nanoseconds. They are described as 4.5 cm diameter and 9.8 cm long and the photos shown in the top of fig 2 of "Low voltage operation of plasma focus" make them appear to be single units in typical electrolytic blue. The papers also claim they are sold for $10/each.

44Th5YA

I am somewhat at a loss to understand this. I was under the impression that there were not electrolytic capacitors for that high of a voltage rating, that they would not be suitable for an inductive pulse discharge with high voltage reversal, and that they would be rather costly; not $10.

I emailed the PI and he responded to my questions about the capacitors with,

Dear myrealname,
Thanks for your comments. But it is true that these capacitors available
in market are working for the plasma focus device and other applications.
This capacitors in India cost around Rs. 600/- (INR) ($10). We are not the
only one to use this. You please see this attached references [(Rohit
Shukla, S. K. Sharma, P. Banerjee, R. Das, P. Deb, T. Prabahar, B. K. Das,
B. Adhikary and A. Shyam, Rev. Scien. Instrum. 81, 083501 (2010)].

With best regards.
Dr. R. K. Rout

The two articles he attached were those I had been looking at and those linked at the start of this post.

Do electrolytic capacitors like the ones described above exist? Has anyone heard of them before? If so, do they have any special name? What company or companies produce them?

EDIT: Sync on #hvcomm IRC has helped me find the company that makes them, El-Ci-Ar, by looking through R. K. Rout's other published articles and finding "Note: Compact high voltage pulse transformer made using a capacitor bank assembled in the shape of primary" which included a slightly closer photo of the capacitor labels. The ones in the journal articles I read seem to be a custom batch but not too far off from their normal stock.

And they aren't electrolytic capacitors like the articles claim. They're probably a custom build of El-Ci-Ar's polypropylene plus double metallised paper design (pdf). That makes so much more sense then a voltage reversal tolerant 5kV electrolytic.

It's a shame that an error made it into two published articles but if the price claim is true $10 for such a cap is still quite a deal.

Forty

Fri Oct 17 2014, 03:03PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

How does one build something as complex as that while not knowing how to identify a simple capacitor?

Have you found anywhere to purchase these capacitors yet?

Superkuh

Sat Oct 18 2014, 02:38AM

Registered Member #59 Joined: Thu Feb 09 2006, 05:45AM
Location: Wisconsin, USA
Posts: 12

I assume it is some sort of language/translation issue rather than a lack of understanding. I am surprised that the peer reviewers didn't spot it though. The only online distributor of the default (2kV not 5kV like the papers) MKP-52 style caps seems to be from Precious Eletronics

. A 2uF 2kV capacitor isn't quite as tempting though.

Signification

Fri Feb 06 2015, 09:37AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

I have been wondering some capacitor specs for a while...

1)Can anyone specify the main differences between an 'energy' capacitor and a 'pulse' capacitor? I have noticed that the 'energy' type tend to have higher capacitance, while the 'pulse' type favor higher voltage than capacitance. But what about an energy storage capacitor with very high voltage and very high capacitance, AND a pulse capacitor with very high capacitance AND very high voltage. In fact it just came to mind: Why would... a pulse cap with it's capacitance (C) higher than it's voltage(V) OR an energy storage cap with V>C be rare??? 'Is this unusual' or am I just not seeing it?

2)I have seen cases where some large energy storage capacitors with labeled ultra-low inductance (uH or even nH) used in applications in circuits containing inductors in series with the capacitor--so, if a MUCH larger inductor is in the circuit, why the expense of using an ultra low ESL capacitor??

Sulaiman

Fri Feb 06 2015, 10:15AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I think that film/foil 'energy storage' capacitors use thinner foil/metallization than 'pulse discharge' capacitors
and electrolytic 'energy' capacitors use more highly etched foil than 'pulse' capacitors
because 'energy' capacitors go for capacitance per volume = larger electrode area
and 'pulse' capacitors are for very high current = thicker electrodes
and thin or highly etched electrodes cannot carry huge pulse currents without deterioration.
but this a just a hazy thought in the recesses of my memory so I'm not certain.

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