Unusual polarized non-electrolytic energy discharge capacitor

[MRMILSTAR]

I saw this Aerovox energy discharge capacitor on E-Bay. What I find unusual about it is that it appears to have a preferred polarity. I seriously doubt that its electrolytic given its voltage rating so why does it have a preferred polarity? This seems to be contradictory to energy discharge applications which typically generate a damped sinusoid which is obviously AC. I couldn't find a data sheet for this series. Is anyone familiar with this capacitor technology?

https://www.ebay.com/itm/High-Voltage-Energy-Discharge-Capacitors-Aerovox-196uF-2200VDC/163973233399?hash=item262d90faf7:g:KbIAAOSwGrBd5wr9

[AndreiRS]

hmmm not really my area, but why not electrolytic..? Microwave oven capacitors are also made of these aluminum cans and have liquid inside and they don't leak. Much.

Well when new at least. I have already seen some leaking, but they were also stuffed.

[klugesmith]

Might there be an internal diode, to minimize voltage reversal in underdamped discharges?

I think the C and V values are in the ballpark for defibrillator applications,
where currents run around 100 A instead of many kA.

[MRMILSTAR]

hmmm not really my area, but why not electrolytic..? Microwave oven capacitors are also made of these aluminum cans and have liquid inside and they don't leak. Much.

Well when new at least. I have already seen some leaking, but they were also stuffed.

Microwave oven capacitors are oil-filled but not electrolytic thus they have no polarity requirements and are perfectly suitable for high voltage AC operation although not energy discharge use. Electrolytic capacitors are filled with a liquid electrolyte, not oil.

Electrolytic capacitors are not recommended for energy discharge use primarily because they are not made for AC operation. They are also not constructed to dump hundreds of amps in tens of microseconds without damage. That being said I have seen them used in disc and ring launchers even though a damped sinusoid of multiple cycles definitely occurs. How long they will last in that role is undetermined but its not a recommended application. I have seen a comment stating that the capacitance degrades rapidly with use in this role thus indicating gradual damage.

[T3sl4co1l]

*Shrug*, check for literature?  Ask 'em?
Family seems to be:
http://aerovox.stage.thomasnet-navigator.com/item/all-categories/apacitors-for-bi-phasic-and-mono-phasic-wave-forms/pn-1719

Ed: cool, this goes into detail! http://manuals.chudov.com/Maxwell/voltage-reversal.pdf

Tim

[klugesmith]

Good find.  Looks like "CD Aero, LLC" came from yet another corporate merger or acquisition.  So long, Aerovox.
And thank you, Tim, for sharing the paper about voltage reversal.

Maybe the wire pigtailed capacitor products are color coded for non-electrical reasons.
Marketing said it helps customers generate assembly and service drawings that are obviously unambiguous about which wire goes where.

Those caps ought to hold up much better than MWO capacitors in crushers/launchers, even if datasheet doesn't mention ESL or voltage reversal or kiloamperes.  You could put a respectable indentation in a beverage can using a capacitor easily lifted with two fingers.  By electromagnetic induction. 

-Rich

[MRMILSTAR]

Thanks for the voltage reversal paper Tim. I did already have that paper though. I found it very useful when I was designing my 6.5 KVA SGTC for predicting the life of my Maxwell 37667 capacitor bank. As I recall it came out to something like 70 years if I operated it for one hour per week! So these should last me for the rest of my life. This assumed that I started with new capacitors, which I didn't, but it sill indicated a very long life.

[T3sl4co1l]

Yeah CDE bought AV a while ago... hmm, can't find a damn thing about when or how(!?), weird.

Presumably, you'll get better life by operating at lower voltage too, not that that's much help for a spark gap unit but you could still make a beefy SSTC that way I suppose.

Tim

[MRMILSTAR]

Yeah CDE bought AV a while ago... hmm, can't find a damn thing about when or how(!?), weird.

Presumably, you'll get better life by operating at lower voltage too, not that that's much help for a spark gap unit but you could still make a beefy SSTC that way I suppose.

Tim

My SGTC uses 6 Maxwell 37667 capacitors in a series-parallel arrangement with 3 strings in parallel and each string consisting of 2 capacitors in series. Since each capacitor is rated for 35 KV, this gives a maximum voltage rating of 70 KV for the capacitor bank. My peak charged capacitor bank voltage, according to JAVATC, is about 19 KV. This gives me a 3.7 peak voltage margin. This derating is where the majority of life extension comes from according to the paper.

[T3sl4co1l]

Yeah that should last about forever... I meant the OP cap, since it's a rather large value and lower voltage.

Tim

[Mads Barnkob]

Those capacitors remind me of those found in defibrillators, both in size and voltage (and opening the link from Uspring I can see that is spot on!)

Their lifetime calculations is based on such a single-use defibrillator is only made to hang on a wall for 5 years and then maybe give a jolt some 5-10 times, then it is thrown away, so that is its designed purpose. Keep that in mind.

Speaking of microwave oven capacitors, those are grossly overrated, maybe not as much anymore, but from what I found some years ago, here is a copy of its data/test "sheet": http://kaizerpowerelectronics.dk/pulse-power/333-joule-moc-capacitor-bank/