Anybody else noticed leakage current through the alternator?

[Denis247]

I still can't see why having the isolator in the + or - circuit of the battery would make a difference.

Isolating either end of the battery isolates that battery full stop.

What am I missing?


btw, even having a machine-sensed regulator in your alternator, if it is connected wrong, will still cause a current drain.

Is your battery remotely located?.

[dnb]

Update:

I found an isolator switch with a much higher peak current rating, so I can use it in line with the starter provided I don't switch it when cranking. This has stopped the current leak flattening the battery.

I have also found the current leak - it was the alternator. It has been replaced, and loads of weird little running issues with the car (like the noisy sensor readings, plus the most annoying one - slow cranking for the first 3 seconds of starting) have completely disappeared. It seems this problem was well worth solving!

[DaveEFI]

The alternator output is permanently connected to the battery. It's the action of the rectifier diodes, which are like a one way valve, which prevents it drawing current with the engine stopped. The most common failure for a diode is to go short circuit. This doesn't stop the alternator charging, but cause it to draw current of a few amps from the battery when the engine isn't running. I can imagine it also producing a strange waveform instead of the normal series of positive going halves of a sine-wave, since the diode bridge removes the negative going ones from the original 3 phase AC signal. The battery will attempt to remove this negative going pulse - but how well it does that will depend on the wiring and other factors.