Fitting an ammeter?

You dont wire the ammeter to the altenator , its wired into the battery , taking all the loads except the starter motor. That way it measures the current flows in and out of the battery. A typical installation might be .... remove all wires from big terminal on starter, except the big fat battery lead, join all these wires together along with one of the ammeter wire, insulate it well as you dont want under bonnet welding (any shorts). Run the other ammeter wire to the large terminal on the starter motor where the others were removed from. turn the main lights on, if the ammeter reads +ve then change the ammeter leads round . steve the grease

I'd chuck the ammeter and fit a volt meter, its simpler, if it reads 14.4 volts then the alternator is working OK.

Peter S

But it doesn't mean that the battery is taking a charge. The only way to see for sure that the alternator is producing an output and the battery is charging is with an ammeter.

Regards Steve G

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In message , R L Driver writes

Installations vary. You'll often find all the supply leads come together on the battery positive terminal rather than at the starter motor, but the principle is the same.

On or around Mon, 15 Sep 2003 10:20:30 GMT, SteveG enlightened us thusly:

but then again, the voltmeter can tell you if the battery is *holding* the charge...

just cos the amps are going through the battery, it doesn't mean the little sods stay there.

Good point. I guess the only complete solution is to have both an ammeter and voltmeter

Regards Steve G

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On or around Mon, 15 Sep 2003 22:10:36 GMT, SteveG enlightened us thusly:

probably. Though you can infer the state of charge from the voltmeter and other behaviour - the other day, when mine was sneakily dropping the battery out of circuit while running, and feeding the electrical loads direct off the alternator, when the lights etc. are off, it shows a slightly higher voltage than normal; with headlights on, voltage is normal but switching heavy loads (e.g. dip to main beam) causes a flicker in the dash lights, as the voltage regulator gets left fractionally behind. Also, at idle, the voltage starts to drop, and if it's in gear, the lower revs at idle make for a noticeable voltage drop.

on a nominal system, it should run anything from 13.5 up to 15V provided the revs are up to about 1500 or more, and shouldn't drop below about 13V at idle, even with lights on.

Fully charged 12V lead-acid, with no load, should be 13.8V, but they rarely are.

when cranking, the voltage shouldn't drop below about 9V unless you're doing a lot of cranking. Discharged voltage is summat like about 7.2V ISTR.