Morris Minor Owners Club

I'm building a remote immobiliser system (long story!), with 4 separate independent feeds to standard SU fuel pump, coil, solenoid and everything else.

I need to know the amperage of both the fuel pump and coil circuits to decide whether I need to use high amp slave relays to switch them.

Can anyone advise the pull-in amperage of the fuel pump? Cos it's essentially an instantaneous pulse, a voltmeter won't react fast enough - I really need an oscilloscope to see the amp draw.

Anyone help with either or both fuel and coil amps?
Ta

Hello Moggles,

running I think about 1 to 2 amps for pump and coil.

As for instantaneous current, do a resistance check and use ohms law, that will give the start current which drops off as the coils energise.

However, I don't think that it is a real worry, after all the ignition switch copes easily enough, and I assume you will close the disabling switches before switching on the ignition anyway so they will only need to be rated for running current.

Alec

Thanks Alec,

My circuit should theoretically handle up to about 2 amps per output. I think that should be ok for the coil, but I suspect is at best marginal for the fuel pump; and I will have to drive a slave relay for the starter solenoid. I will see if I can get a static resistance reading on the fuel pump as you suggest, but I still reckon the instantaneous spike may be a problem.

Cheers,

As Alec says - the in-rush current is entirely dependent on the initial resistance you measure on the coil. As the coil saturates - the current decreases.