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 initial inrush current will be very substantial. It is only limited by the impedance of the supply and the very low impedances introduced by the rectifier, the capacitor, and connections.
The inrush current may be limited by adding a resistance in series with the input. 10 ohms will limit the inrush to about 25 amps, which is within the very short term capacity of any likely fuse or MCB.
A better plan is to use an inrush current limiter or NTC device, this has a high resistance when cold, and thereby drops a significant proportion of the supply voltage and limits the current. As the device heats up, the resistance reduces and introduces only very limited losses.
I have done similar, to keep mains voltage LED lamps lit for a minute or more.
The initial inrush current will be very substantial. It is only limited by the impedance of the supply and the very low impedances introduced by the rectifier, the capacitor, and connections.
The inrush current may be limited by adding a resistance in series with the input. 10 ohms will limit the inrush to about 25 amps, which is within the very short term capacity of any likely fuse or MCB.
A better plan is to use an inrush current limiter or NTC device, this has a high resistance when cold, and thereby drops a significant proportion of the supply voltage and limits the current. As the device heats up, the resistance reduces and introduces only very limited losses.
I have done similar, to keep mains voltage LED lamps lit for a minute or more.
