My capacitor bank consists of 32 330V/400µF foto flash capacitors connected to 1320V/800µF (700Ws), the power switch, a discharging relay and the charging/control-circuit. Below you can see the "power board". On the lower right is the power switch. An RC-servo is used to close the contact consisting of a steel screw and a steel plate. The controlling circuit was removed as servo electronics are bothered by the emv produced by the discharge (and it was dead anyway :-). Instead there's an end switches and a relay logic...emp safe! The homebrewn discharging relay is normally closed (so it automatically discharges the capacitors in case the circuit breaker trips or something).
The control board. At the botton there are three switches (main power, discharge
and charge) and a pushbutton (fire). At the right side you can see two transformers
for the discharging relay and the power switch and one of the two relays used
to control the power switch. When the fire-button is pushed, the servo motor
is connected to DC power via a resistor (to limit the stress on the gear and
the motor when the switch is closed). When the button is released the motor
reverses direction (no resistor this time - the motor needs as much current
as possible in case the contact is spot-welded together). Once the end switch
is pushed, the motor is shorted to act as a brake.
The charging circuit consists of an isolation transformer which is connected
in series with mains (to get a voltage of 460VAC). Using two diodes I get a
maximum charging voltage of 1300V - no danger of overcharging the capacitors.
The charging current is limited by two lightbulbs in series, due to the ptc
characteristics the capacitors can be charged faster than with linear resistors.
The multimeter is used for monitoring the charging voltage.
I've found 40 385V/950µF foto flash capacitors (2.8kWs) at a hamfest,
now I'm using 36 of them instead of the smaller capacitors. But now the charging
takes forever and I can't charge them to their rated voltage either. I'm going
to use a small MOT for charging. The plastic gear of the servo didn't stand
the strain very well and is quite wobbly now. I'm going to build a new power
switch using a wiping motor from a car instead. And I think I can replace the
discharging relay with two (smaller) commercial relays. In other words: As soon
as I find the time I'm going to redesign the whole capacitor bank.
The capacitor bank (700Ws version) in action, vaporizing a piece of Al foil. Aluminium produces a very bright flash and seems to react with oxygen, thus bursting the detonation energy even more.
Exploding steel wire - one hell of a sparkler!
