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Are capacitor charging circuits necessary? Answered

So I was looking at some coilguns and all of them have a circuit to control the charging, is this really necessary or can you just apply the voltage you want and let them charge.

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Unless you power supply will be damaged by the initial current spike, all you need is a switch to disconnect the supply, and connect the coil. Even then, a low value resistor is all that is necessary to limit the current.

The charging circuits are usually to provide a few hundred volts to the capacitor bank from a low voltage battery or power supply.

Remember, if you charge DOL, then there's a good chance you'll blow a fuse or throw a breaker without a current limit...

I'm planning on bringing the voltage up to around 300v-500v and I don't want a big light bulb on my thing, I want it to be hand held. And I guess this is what the guys I am talking about have, but how hard is it to make a device that uses rapid on and off to limit the power, instead of wasting power and heat on a resistor.

Just use a power resistor. You aren't wasting much at all, if you work it out.

If you're going for direct-on-line charging, just put a 20W mains bulb in series with the cap and supply.