A friend of mine brought a little device he made its a bridge rectifier fed straight off the mains then fed into a 900 uF capacitor the purpose of this little device is to try to make a CFL stay on for 10 seconds I don't know why it's his project. We tried this device out and after a few switch ons it popped a 5 amp fuse in the feed to my test bench so the question is what would be the charge current for a 900 uF capacitor? It made the ammeter in the feed to the test board kick up. So is there a way to work it out?
The capacitor maker will quote an ESR, or a tan delta that you can work it out from. I'd expect fractions of an ohm, so inrush several hundreds of amps, but depending exactly where in the mains cycle you switch on - you may have been lucky a few times and switched near the zero crossing. But you do not need it to be that fast starting, and the violent surge is not good news for the capacitor or the light switch either.
As others have said some series R either before or after the rectifier chosen to dissipate less than a watt in normal operation is needed. Note that during switch on the full mains voltage will be across that resistor, and you may switch on at the crest of the mains (300 plus volts) when the cap is totally flat. beware of resistors not rated for 240V - 2 smaller ones in series may be preferred.
The capacitor maker will quote an ESR, or a tan delta that you can work it out from. I'd expect fractions of an ohm, so inrush several hundreds of amps, but depending exactly where in the mains cycle you switch on - you may have been lucky a few times and switched near the zero crossing. But you do not need it to be that fast starting, and the violent surge is not good news for the capacitor or the light switch either.
As others have said some series R either before or after the rectifier chosen to dissipate less than a watt in normal operation is needed. Note that during switch on the full mains voltage will be across that resistor, and you may switch on at the crest of the mains (300 plus volts) when the cap is totally flat. beware of resistors not rated for 240V - 2 smaller ones in series may be preferred.
