Electronics 2000

Hello

I'm hoping someone here will be able to help me, I have very little experience with anything electrical but have a project which involves connecting a dc motor to a pwm controller. My question relates to the use of a fuse within the circuit, as I understand it, when an electric motor is switched on there is a surge of current, usually around three times the maximum amperage the motor is rated to. What I don't quite understand is how to create a circuit which operates at the motors maximum amperage without blowing the moment the motor is switched on. For example, the motor I'm looking at is rated 9.5amps, when switched on there will be a spike to 28.5amps, if I put a 28.5amp fuse on the circuit it seems to me there may as well not be a fuse there as it won't protect the circuit from any problems, by the time the fuse has blow the motor or the controller will have burnt up. Also, should the controller be rated to the spike or the useful output of the motor?

I'd be very grateful for any answers.

Warm regards

Robbob

Hello

I think it's sorted, if I understand right I shouldn't need a fuse, I'll just rate the pwm controller above the spike so that it doesn't fry and make sure I don't stall the motor, or at least if I do stall it shut the motor down immediately. It will be powered by a battery so I don't think there's anyway it can draw more current than the battery can supply, so the power source will be ok.

Regards

Hi

It is essential to have a fuse on the feed from the battery, if only to protect the wiring. A battery capable of running the motor you are talking about is presumably quite large; the short circuit current could be 100's of amps and easily melt wiring / circuitry or start a fire. I'd suggest using an anti-surge fuse with a rating lower than that of the wiring & circuitry, but above the normal running current of the motor. Try around the 12 amp mark, ensuring the wiring is rated to this.

It would be wise to supply the PWM controller via a smaller fuse (< 1A) unless all the circuitry is rated to the capacity of the larger fuse.