Voltage conrolled switch

[WilliamN]

I just built a charger circuit and capacitor bank for my coil gun. The charger takes 12v dc and charges my cap bank in about 5 seconds. Cap bank is 15 capacitors @ 330uf/450v. The thing charges them so fast I want to build a circuit that can shut the charger off as soon as the caps reach 450V. How would I go about this? I thought of using a comparator with a voltage divider. And the output of the comparator going to a normally on transistor at +12v in point in the charging circuit. Because of the high voltage and current I really don't know how I should wire it up. Any help would be greatly appreciated! Thanks. I included a graphic to show what I am thinking.

 

[TillEulenspiegel]

William this can be done in a few ways, but it would be helpful to know the specifics of the charging circuit. 12VDC in and ? out. Is it a switching supply? At these voltages and stored charges , You want to be careful what You do The best at overcharging you can expect is a lot of smoke and some expensive caps that are trash, the worst ..well not good. Normally regulating circuits are based on current draw of the load.
I assume that your using a DC V at higher then the rating of the caps , hence the quick charge.
More info would help

 

[Optikon]

I just built a charger circuit and capacitor bank for my coil gun. The charger takes 12v dc and charges my cap bank in about 5 seconds. Cap bank is 15 capacitors @ 330uf/450v. The thing charges them so fast I want to build a circuit that can shut the charger off as soon as the caps reach 450V. How would I go about this? I thought of using a comparator with a voltage divider. And the output of the comparator going to a normally on transistor at +12v in point in the charging circuit. Because of the high voltage and current I really don't know how I should wire it up. Any help would be greatly appreciated! Thanks. I included a graphic to show what I am thinking.

An idea..
1) use an optocoupler that on the diode input side has several 100V zener diodes in series with a resistor. When the capacitors reach 450V, the zener diodes conduct and a little bit of current flows through the input diode (limited by the resistor)

2) The output of the opto will go to a simple circuit that drives your series pass transistor in the charging path. This signal could force your transistor to cutt-off.

 

[Nigel Goodwin]

You wouldn't usually turn the inverter off, you design the inverter to provide 450V, so it only charges the capcitors to 450V.

 

[WilliamN]

Cap charger

Yes I did that,(approx 450v output) but it took too long to charge my cap banks. I have multiple 15 capacitor cap banks. My charger needed to be able to charge all four of them. Right now Its just charging one for experimental reasons. Hence the 5 second time. I am sure the time will go up when I hook up all the banks. They will all be isolated from each other as each bank will power a seperate coil.
I want each cap bank will get a voltage controll mechanisim. Once all four banks stop drawing current from the charger it will then shut off. And I'm ready to fire. :lol:

 

[Roff]

How much current (in the 12v line) are you going to switch?