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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
You dont need to calculate to see obivous, energy is always same otherwise you could rewire charged caps and make prepetuum mobile :D
Line voltage is 220V, vhen rectified hangs around 300 but still too high to charge 3 in series. Il use transformers for low voltage supply and AC supply for charging transformer. Or maybe even boost converter/SMPS may be good for voltage regulation.. ?!
200V seems best as in any case transformers must be used. Also I have original rails that connected capacitors in 3vs 3, just practical !dodge
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
126000uF, 100V(the caps connected in parallel) shorted through 1ohms will discharge in .5-.63sec at peak amperage of 100A. Joule rating is .5C(V)(V) = 630J. 3500uF, 600V(the caps connected in series) shorted through 1ohms will discharge in .014-.018sec at a peak amperage of 600A. Joule rating is still .5C(V)(V) = 630J
Thus, you can see that in the first selection, 630J is discharged in .5-.63sec, but in the second selection it is discharged more than 30x faster! Plus, you have a higher peak current rating.
Its true for external load of 1 ohm, but here we just say external load is 0 (imposibble in reality) and consider only internal resistances of caps, thats what im talking about. In series they cannot give more current than 1 cap would give, because their resistance is 'stacking' with voltage, we get only max voltage but not in (maximum) current. This really may be better for SCR-s as the would need to switch lesser current... Parallel capacitors can give six times more current than one but voltage is lower so external load limits current more...
I think it doesn't really matter so much after all, now i decided 3 vs 3 in series :)
SO I have 2 1000uF 300V Electrolytic Caps for a coil gun. Is it better to hook them in series for 600V 500uF?
This are rather smll caps but some mini coilgun could be made. paralell is better as your switching device doesn't need to handle large currents for long, actually again i think its not real problem...
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
Firkragg wrote ...
Switch is far bigger problem, I dont like to go arcwelding so mechanical switch cannot be just a solenoid pushing some metal conductor, that will surely weld and dissipate far more power than intended target. Solenoid is simple and good idea for triggered gaps, but not for direct contact switching. conclusion: I must buy SCR.
Registered Member #102
Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169
I used very large relays in one of my coil guns, and I had great results. They were 2kj banks The switch is one of those things that are easy to replace. I'd go with a large relay, and get an scr later. Kolas
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I have some contactor switches but im afraid to weld and ruin them... Also I have acess to big omron relay with visible and easily acessable contact, but it is still too small for that current...
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Oh, btw, for charging voltage I don't really see the problem of charging to 200V or 300V from mains. In practice you will need some kind of current limiting which drops voltage anyway, and if you supply voltage is not higher than the cap voltage, charging will take literaly forever.
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six hundred precious joules
