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What can I do with 64uF @ 4kV?

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SpaceWyzard

Tue May 30 2017, 12:22AM

Registered Member #2318 Joined: Fri Aug 28 2009, 01:22AM
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Posts: 33

I came across 8 8uF 4000v capacitors. The package looks similar to a microwave oven capacitor but about 3 times as large physically. I'm not sure what they came out of. Assuming I hooked them all together in parallel, is this enough to do any cool hv capacitor bank stuff like coin shrinking or can crushing? If not, what could I do with them? I hate to just let them sit there on the shelf.

klugesmith

Tue May 30 2017, 12:56AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

With those numbers, you can make a respectable can-crusher.
Depending on the capacitors' current rating, which depends on internal construction details, it could be a long or short-lived can crusher. Got any pictures to share with us? Are they by any chance defibrillator caps?

It's not necessarily optimum to connect them all in parallel. The potential can-crushing performance would be about the same if you run them all in series, or in a series-parallel combination (what RC model enthusiasts might call 2S4P, or 4S2P). Those configurations all have different requirements for charging supplies, discharge switches, resistors for voltage balancing, bleed resistors for safety, and optimal work coils. Crushing efficiency, and electrical stress on the individual capacitors, will be about the same for all those configurations.

All in parallel could be a good choice for general safety and ease of construction. You might find it likes 3 or 4 or 5 turn work coils. Bank configurations with lower capacitance and higher voltage would, in my unpracticed opinion, work best with coils that have more turns in about the same proportion.

SpaceWyzard

Tue May 30 2017, 01:02AM

Registered Member #2318 Joined: Fri Aug 28 2009, 01:22AM
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Thanks for the quick reply! I don't have any pics at the moment but I'll post some tomorrow after work. Glad to know I'll be able to use these for something!

teravolt

Tue May 30 2017, 01:35AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

you could also make a ring launcher charge it with a microwave oven transformer

SpaceWyzard

Tue May 30 2017, 02:12PM

Registered Member #2318 Joined: Fri Aug 28 2009, 01:22AM
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Posts: 33

So this is not my pic but I found one on ebay just like the ones I have. It is priced on ebay at 75$! And I got 8 of them for free! I had no idea they were so pricey!

Anyway, do you think these would hold up under pulse-rated activities? Or are they gonna die after a few shots?

hen918

Tue May 30 2017, 03:11PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

careful, the case is one of the terminals. looks like parallel is definitely best

klugesmith

Tue May 30 2017, 07:31PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Another warning. Those capacitors, and things you make with them, can deliver lethal electric shocks. As dangerous toys, they are in a league with microwave oven transformers. Maybe more dangerous, because (among other things) ...

1) high voltage can persist long after the apparatus is turned off or unplugged.

2) MOT's have intrinsic current limiting. HV capacitors don't.

I hope that when we see pictures of your windfall, the shorting wires or bleed resistors will be visible.

You might also want to look up dielectric absorption in capacitors. After a rapid discharge from HV to zero volts, if the load is disconnected right away the voltage will creep back up. A minute later, it could be enough for a painful and surprising shock, with consequential personal injury or property damage. The effect is not a problem with MO capacitors, because they have built-in bleeder resistors.

SpaceWyzard

Tue May 30 2017, 09:35PM

Registered Member #2318 Joined: Fri Aug 28 2009, 01:22AM
Location:
Posts: 33

Got it. Definitely use bleeder resistors. I like living and all my digits so no problem there.

radiotech

Fri Jun 02 2017, 02:53AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

Will 64 joules flash a Xenon lamp sufficiently to excite a ruby rod into lasing ?

Dr. Slack

Fri Jun 02 2017, 06:53AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Even though case is one terminal, you need not connect them all in parallel. A bipolar 4P2S configuration with all cases grounded would let you double the voltage and still have no more than 4kV to ground. However, the +4/-4kV terminals may complicate the switching/charging/loading. Happy can crushing!

BTW, there's more than one way to crush a can. As well as the obvious 'turns round the middle', there's also the pancake ring-launcher stylee. I made a spiral pancake coil of IIRC 8 turns of insulated 4mm wire which conformed closely to the bottom of the can. This launched the bottom of the can through the top, and smashed the whole thing into the ceiling.

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