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Registered Member #1628
Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95
I have a surplus suppply of many Sangamo direct current capacitors. I would like to make a quarter crusher with them if possible. They are rated 15kvdc 2.25µf.. If I connect 20 of them in parallel it comes out to about 5kjoules. Will this work or do I need to use different type capacitors? Any help is appreciated. Thanks in advance. Bamacoiler
Registered Member #1917
Joined: Fri Jan 09 2009, 02:38AM
Location:
Posts: 62
5kJ may not be enough energy to crush every type of coin you come across, but it should be sufficient for enough of them to make it worthwhile (you won't, however, be able to smash coins into blobs of molten metal ). There are a few important aspects of the system that you need to consider before building it; Peak current rating of the capacitors - they should be rated as energy discharge capacitors, and the sum of their discharge current ratings should be greater than what you expect the device to produce (using simulations, you can at least get a baseline estimate). Assuming that they each have a 25kA rating, 20 in parallel will result in an overall rating much higher than you need. Voltage reversal rating - in any pulsed power application, there is likely to be voltage reversal. The specification sheet for the capacitors will have a graph of the deratings incurred through a range of voltage reversal values, usually from 10% to 95%. There will be a reversal rating printed on the caps; if the reversal is held to that level, the derating factor is one, and higher reversals result in a higher derating factor. Even in a coin shrinker, where the inductive load disappears very quickly, there is still voltage reversal (imagine how long you could draw an arc at 100kA...), and it has to be factored into the design. As far as I know, this is usually countered by using the capacitors at lower than their rated maximum voltage, which increases expected lifetime. In your case, that won't really be an option, so you may want to research alternative methods. Compatibility with future upgrades - if you later come across caps with a vastly different voltage rating, you'll not be able to use both sets to their full potential at once. In the case of these 15kV caps, that shouldn't be a problem, since most coin-shrinking rigs operate in a similar voltage range, and capacitors in that range are (relatively) easy to come by.
Then there's switching, insulation, and confinement of the work coil to be considered. A coin shrinker is an expensive, heavy, loud, and possibly very dangerous device. You'll want to do lots of research and design work before you attempt to build one, but these caps (if they are energy discharge rated) are a good place to start.
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Quarter Shrinker Question
). There are a few important aspects of the system that you need to consider before building it;