Re: Which capacitor for quarter shrinker?
Posted by Bert Hickman on 7/22/2018, 4:07 pm, in reply to "Which capacitor for quarter shrinker?"
Actually, the Aerovox cap is the better choice. You may be misinterpreting the voltage reversal spec for this cap. The DC rating of 22kV with 20%VR means that the cap is actually rated for a maximum peak-to-peak voltage swing of 22*1.2 = 26.4 kV. You can safely charge this cap to over 13 kVDC (7.2 kJ) in a ringing coin shrinking or high-Q can crushing application.
I use a maximum of 6.5 kJ (with a pair of 70 uF 12 kVDC caps in parallel) with excellent results. You can actually charge this cap to even higher energies during coin shrinking since the work coil explodes shortly after the first current peak, and the lossy plasma ball (after the coil explodes) tends to damp subsequent ringing. The caps have withstood over 7,000 shots with no problems (other than me accidentally freezing a couple).
BTW, if you don't already have it, following is a nice paper on voltage reversal and lifetime from Maxwell, "THE EFFECT OF REVERSAL ON CAPACITOR LIFE":
We corresponded a little bit about this recently on TCML and I got some useful information from you. I had a few more questions but since they regard quarter shrinkers I didn't want to abuse the TCML subject matter restriction.
My question concerns which of 2 energy discharge capacitors that I own, should I use for my quarter shrinker? The capacitor specs are as follows, some of which came from you (thanks):
Capacitance: 100 uF
Maximum Voltage: 22 KV
Maximum voltage reversal: 20%
Capacitance: 100 uF
Maximum Voltage: 10 KV
Maximum voltage reversal: 80%
On the surface I would pick the Aerovox because of its higher maximum energy storage (24 KJ), even though I will probably never use that. However, its 20% voltage reversal indicates that I can only charge it to 4.5 KV without exceeding its voltage reversal spec.
The Maxwell with its 80% voltage reversal spec indicates that I can charge it close to its maximum 10 KV without exceeding its 80% voltage reversal spec.
I suspect that the Aerovox will tolerate more than its 20% rating for this application because I will probably only be firing it a maximum of a few hundred times over its life.
Does your experience indicate which of these capacitors I should use?