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Talking about can crusher/coin shrinker capacitors

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Kizmo

Wed Jul 04 2007, 04:34PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Hi!

Im planning to build quite strong (over 2kJ) can crusher/coin shrinker/potato destroyer etc. I found these caps from ebay:

K75-40a (Not used, in wooden box, Old stock)
5000V (5kV)/ 50uF / 10% tolerance

-POLARITY: Any DC or AC

-Peak Working Voltage: 7500 V

-Very low inductance (ESL < 35 nH) and low ESR

-Discharge current amplitude: up to 1400 A

-Dissipation factor at f=50Hz: <0,008 !

-Time constant: >3000 MOhm.uF

-Insulation resistance: >15000 MOhm

-Single shocks witch acceleration: up to 500 G

Temperature range: -60...+70Â°C (-76...158Â°F)

Atmospheric pressure of work: 0,00012 to 294 000,0 Pa

Working Position -Any

Material of electrodes:Composite of metals witch a special film coats

Electrode insulator: Polyethylene-tereftalate

Im ready to buy 2 or 3 of these, good idea? (price doesn't scare me as long as i can be sure that it actually works)

Dago

Wed Jul 04 2007, 05:01PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

The 1400A peak current rating is quite low, surely too low for can crushing/coin shrinking applications where the peak current can (and has to, to get the desired effect) rise to tens of kiloamps.

Kizmo

Wed Jul 04 2007, 05:29PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Where to get caps like that?

J. Aaron Holmes

Wed Jul 04 2007, 05:43PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Are you sure the 1400A figure is really the maximum current the cap would source when shorted, or is that "just" the *rated* maximum? I kinda doubt most people who build can crushers and quarter shrinkers are operating within the ratings of the caps. Don't most people who build these devices use those "energy storage" (not pulse) caps and just rely on the very low number of pulses to keep the cap from self-destructing?

Cheers,
Aaron, N7OE

Kizmo

Wed Jul 04 2007, 05:47PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Actually *rated* maximum for this cap is 2000A, it might be that it gives much more when hard-shorted, but doesn't last so long.

...

Wed Jul 04 2007, 07:12PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The max current you could source from this cap is limited only by the total R and L of the circuit, and considering this cap has only 35nH of L, we can probably assume that the ESR is negligible, you are really only limited by the work coil. How many shots the cap will survive before self destructing is hard to say, but I would say you should be able to get plenty of fun out of it.

Marko

Wed Jul 04 2007, 09:04PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

625 joules isn't all too much, and I noticed these caps are really cheap, so you might be well by using a lot of them in paralell. I looked at them on ebay and 2000 amps really doesn't sound all that unrealistic for their wimpy therminals.

Dago

Thu Jul 05 2007, 12:29PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

J. Aaron Holmes wrote ...

Are you sure the 1400A figure is really the maximum current the cap would source when shorted, or is that "just" the *rated* maximum? I kinda doubt most people who build can crushers and quarter shrinkers are operating within the ratings of the caps. Don't most people who build these devices use those "energy storage" (not pulse) caps and just rely on the very low number of pulses to keep the cap from self-destructing?

Cheers,
Aaron, N7OE

I think tesladownunder and Bert can shed more light into this but I'm pretty sure they are running inside the ratings of the caps. They are using specialized pulse caps with flat low-inductance terminals and the caps are specced for atleast a few tens of kiloamps per cap IIRC.

Steve Ward

Thu Jul 05 2007, 03:37PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I kinda doubt most people who build can crushers and quarter shrinkers are operating within the ratings of the caps. Don't most people who build these devices use those "energy storage" (not pulse) caps and just rely on the very low number of pulses to keep the cap from self-destructing?

Nope, from what i have seen most of us that do coin shrinking or other heavy duty pulse energy work have the "real deal". My maxwell is rated for 100kA pulses and 200kA for shortened lifetime. Bert uses 4 such caps on his shrinker just to make sure they last forever since he can run them at far energy per cap that way. TDU's cap bank is also rated for 100kA per cap i think (with 3 in parallel!).

The 2000A peak rating worries me... but then again i did slightly shrink dimes with 18 parallel microwave oven capacitors charged to 8kV! Of course, microwave oven caps were cheap at 1 dollar each, so i could care less if one failed.

GreySoul

Thu Jul 05 2007, 03:44PM

Registered Member #546 Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239

fwiw...

my 38KJ bank is rated at 100KA and I'm sure it's seen heavier duty in it's lifetime before I got it. The bank is 4 x 10kv @ 194uF Aerovox energy storage caps.

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