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Registered Member #58215
Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
Signification wrote ...
You know that would then knock your capacitance down to 50uF, which may be OK. You would need FOUR 100uF @ 5kV capacitors to get 100uF @ 10kV (2s2p). If over 1kJ is involved, I try to avoid "series".
He originally wanted 60uF, 50 would be fine. I'm not sure if the added ESR in series would harm or not.
Kizmo wrote ...
You dont need 1kJ for can crushing. 1kJ from proper pulse capacitor will tear the can in half.
I think he wants to tear it in half. I'm not sure. This is his senior project, not just a fun garage thing.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
...Almost surprising as the low energy is the very small magnet wire used -- 18AWG (5 turns)--shield it!
We see lots of overdesigned work coils.
As discussed here before, a conservative I-squared-t rating for 18 AWG wire is 7,344 A-squared-s. A hypothetical 15-microsecond rectangular pulse could be 22127 amperes without overheating the wire.
SteveHV appears to be one of those abusers who gets away with putting 8 kV on 2 kV (AC?) MWO capacitors. 576 J would be 8 kV on 18 microfarads, e.g. 9600 A for 15 microseconds. The wire will just get a bit warm. A simpler way to size the wire is to figure the mass of copper to absorb 100% of the initial capacitor energy without getting too hot.
It would be reasonable to ask if the 18 AWG wire is strong enough to resist the Lorentz forces. Pretty likely, since "inductive repulsion" creates a pushing contest between the coil of copper wire and a ribbon of 0.1-mm-thick aluminum.
p.s. 25 joules in a 4 or 5 turn coil is enough to make a detectable indentation in a beverage can.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
klugesmith wrote ...
...Almost surprising as the low energy is the very small magnet wire used -- 18AWG (5 turns)--shield it!
We see lots of overdesigned work coils.
As discussed here before, a conservative I-squared-t rating for 18 AWG wire is 7,344 A-squared-s. A hypothetical 15-microsecond rectangular pulse could be 22127 amperes without overheating the wire.
SteveHV appears to be one of those abusers who gets away with putting 8 kV on 2 kV (AC?) MWO capacitors. 576 J would be 8 kV on 18 microfarads, e.g. 9600 A for 15 microseconds. The wire will just get a bit warm. A simpler way to size the wire is to figure the mass of copper to absorb 100% of the initial capacitor energy without getting too hot.
It would be reasonable to ask if the 18 AWG wire is strong enough to resist the Lorentz forces. Pretty likely, since "inductive repulsion" creates a pushing contest between the coil of copper wire and a ribbon of 0.1-mm-thick aluminum.
p.s. 25 joules in a 4 or 5 turn coil is enough to make a detectable indentation in a beverage can.
If you've got good pulse discharge caps though, the resistance of the coil could limit the peak current. Yes, the coil might only get warm, but that energy isn't going into the can.
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[moved] Where to get high voltage capacitors (10kV+)
