Procrastinatus

Why talk about it now?

You can never have enough capacitors

Posted by aonomus on January 26, 2009

So one of my next projects is going to be a (slightly insane?) 3kJ electrolytic capacitor discharge bank using a mishmash of 450V caps. My current collection is as stands:

4x Aero M Inverter Grade 3100uF 450V caps

4x Nippon Chemi-Con Computer Grade 3300uF 450V caps

6x Cornell Dublier 1500uF 450V caps

I plan to purchase another 4-6 of the Aero M capacitors as cash becomes available, inverter grade capacitors stand a better chance at surviving extreme current discharges.  I will likely replace the 4 Chemi-Con caps with 4 more inverter grade caps, and eliminate the CDE caps completely (save them for another project, perhaps a multi-stage CG).

The capacitor bank will be switched by a Powerex C397 Hockey-puck SCR rated for 5500A non-repeating surge current, and I will likely invest in some beefy stud diodes to place in-series on the opposite leg of the capacitor bank to minimize the ringing that will occur due to voltage reversal in inductive loads.

The reason for the series diode is that for any inductive load, there will be significant ringing resulting in voltage reversal. Electrolytic capacitors do not tolerate reverse voltages, especially when swinging from -300 to +300 in rapid succession. A example LCR simulation based on a can-crushing coil results in some… interesting figures.


All in all this should be an interesting project, having a 3kJ capacitor bank will allow for some experiments in coilguns, railguns, magnetic launching, magnaforming, can crushing, and wire exploding.

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