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Registered Member #4148
Joined: Tue Oct 18 2011, 01:08PM
Location:
Posts: 5
Has anyone tried using car audio capacitors? If this equasion (1/2 x Capacitance (in F) x V^2) is correct, the capacitance is as important as the voltage. I have found car audio caps as high as 35F 16V for 4,480J (though there may be higher out there). Is it due to the cost/size of these caps or is the higher voltage needed to allow proper coupling? If the later is the case wouldn't it be possible to use a Cockcroft-Walton or Dickson voltage multiplier after the caps and before the coil? I have looked for similar threads and have not found the answer. I apologize if this question has already been answered or if my lack of experence is showing through.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Yes, this question has been answered many a time before. Car Audio capacitors have a large ESR, and thus can not discharge fast enough to be effective in a coilgun scenario. You generally want very very fast rise times.
Registered Member #4148
Joined: Tue Oct 18 2011, 01:08PM
Location:
Posts: 5
The one I mentioned prevously has (or is advertised to have) an ESR of 0.015 Ohm @ 120Hz/25ºC. This is too high? I have been unable to find ESR for photoflash caps to compare. Does anyone know offhand?
I just found a photoflash cap w/ 6300µfd 400 volt 28 milliohms ESR... as in .028? Am I missing something?
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
You are missing that the maximum current delivered from the higher voltage capacitor is a lot higher. If you put enough 16 V capacitors in series to get 400 V then you get 0.375 Ohm.
It does not mean that you can't make a usable coil gun at 16 V, you just need to design it with that in mind to get the most out of it.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
6300uf for a photoflash? damn. you'd give people a tan every time you took their picture. I guess you could make a coilgun with those supercaps but you'd need a ton of stages and very complex switching in order to get the same effects as a higher voltage capacitor and a single stage.
Registered Member #3930
Joined: Sun Jun 05 2011, 07:27PM
Location: Sydney, Australia
Posts: 33
Forty wrote ...
6300uf for a photoflash? damn. you'd give people a tan every time you took their picture.
God yes thats a huge capacitor for a photo flash - mabye its the cap out of an alien bee?
That size I'd expect to see in the psu of a small air cooled argon laser. In fact I have one right here - 6800uf, 160V that came out of one. Naturally xenon tubes need a higher voltage to work, but heck that cap came out of a laser with a tube a foot and a half long. I'd be surprised if even a big xenon tube a few inches long would survive a 6300uf discharge more than once :)
I do have a cap here from a pro photo strobe, and its rated 840uf 400V. Did the OP accidentally get an extra 0 in there?
Registered Member #4148
Joined: Tue Oct 18 2011, 01:08PM
Location:
Posts: 5
Yeah, I was only comparing ESRs... I'm not planning on spending so much, nor using one as large as the first. Just wondered if anyone had tried, why/why not, and if low voltage/amperage could be compensated for... Thank you all, for the input so far...
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Car audio caps?
