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Registered Member #259
Joined: Sun Feb 26 2006, 05:57PM
Location: Friday Harbor, Wa
Posts: 18
I have still not succeeded in getting anything more than inch long sparks from this coil even though I have been working on the "finished" design for months. You will probably remember me from my other posts asking past problems with it. I have still not narrowed it down. The coil:
MOT supply
4x voltage multiplier (cockroft walton, with 2 942C caps in series for each capacitor, 2 stages)
1 MOT inductor, 'I' cut off, handwound coil (1000 turns) to insulate the windings so it can better withstand 10,000 volts.
This is a Resonate DC system. So far maximum spark length is 3 inches, usually less. The problem seems to be with the spark gap. Even at full power the BPS sounds much less than what it should be, and the gap sparking is intermittent. It fires for a certain interval, then doesn't fire for awhile, then starts firing again. I designed it with very little weight ( the arm is only 2" in diameter, .25" plexiglass, and with a small screw going through each side), and the gap between the screws must be less than 2mm, otherwise the intermittent fireing worsens, or does not fire at all. This is stange, because even at 10,000v it should fire at 1 cm, and this DC resonate system theoretically runs at 20,000v, which should be at least 1.5 cm. This is driving me crazy! Does anyone have any helpful ideas?
Registered Member #188
Joined: Thu Feb 16 2006, 05:18PM
Location:
Posts: 67
What capacitor value are you using for the voltage multiplier? You will need at least some µF so get any good output power. Look at steves design with series strings of electrolytic capacitors.
Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
The gap fire at the maximum voltage, so, if it misses to fire, the primary cap is charging too slow. You need more charging current from your multiplier. 942C caps are 150 nF each? Then, with two in serie per stage, you try to charge at 10 kV a 12.5 nf cap using a 75 nF cap...is too low. The cap in the multiplier has to be at least 100 x times bigger than the primary cap.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Do you have any high voltage probe? If not you can get a string of caps going to give you a good HV divider to see whats going on. You would need 1000pF 1kV caps X 30 and put 3 in parallel for ~ 333pf 1KV then do that 10 times, then to a 10K 2 watt resistor for a cheapie quick and fairly accurate divider, this was the first one I made.
It sounds like what you effectivly did was insted of build a multiplier, you have a divider like my example above, or like was said earlier is that you're just swamping it out with too high a current demand for the caps to deliver.
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further resonate DC problems
