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VauxCav isuzu alternator

Hi,

I think I have a problem with the alternator.

Rev counter works intermittently. When working 14.2V accross terminals, 18V measured at the first connector from main output from alternator (separate large red wire). I haven't checked if there is an output here when the rev counters not working.

When rev counter doesn't work no charging - as measured accross battery terminal ~12.7 engine on or off.

Battery light sometimes comes on with the ignition sometimes not. Always out when engines running.

Why has this alternator got so many wires!

Can some tell me what each of the terminals are for?

I know the green wire goes to the rev counter (straight from the stator/half rectified?).

Which wire supplies the initial current to the slip rings - red/yel ? earthed through casing?

What are the black and smaller red wire for. Does the black sense the battery voltage i.e input to regulator. I would guess most likely the alternator is knackered or an intermittent fault on the circuit supplying the slip ring.

Any suggestion on how to proceed?

Thanks

Jim

Reply to
Jim Ingram
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I'm guessing the 14.2V is across the battery terminals? And the 18V is measured at the alternator output terminal?

If this is the case, then there is a bad connection(s) between the alternator and battery. This is easily checked by connecting a voltmeter between the alternator output terminal (B+), and the battery positive. Do this just after the engine has been started, so the alternator output is still quite high. The voltmeter reading should ideally be 0V, but anything upto about 0.2V would be acceptable. If the reading is higher than this, it's a case off gradaully measuring the voltdrop across various connectors/cables until you find the bad connection(s). You'll also have to repeat this for the earth side, by checking for any voltdrop between the alternator casing and battery negative, in a similar way to checking the positive wiring.

Takes a feed from the main stator output before it goes into the rectifier.

Slip ring current is done by the built in regulator

One wire will be the ignition light, and the other could be a battery sense wire (would make sense, that the alternator puts out 18V yet the battery voltage is still maintained at 14V)

Check for any bad connection as above

Reply to
Moray Cuthill

Isn't there a plug further up from the alternator that corrodes?

Reply to
Angus McCoatup©

Thanks all. The alternator was at fault. My 18V was a red herring as I'd measured it with no connection between the main terminal and battery . I don't know exactly what was wrong with the alternator but since without the engine running , the main alternator output terminal disconnected from the battery and the ignition on I was measuring around 11V at the main terminal there had to be at least one diode blown.

There is still a slight voltage drop between the +ve battery terminal and alternator but it's only 0.26V which I can't find the source of (I'll probably just add an extra cable between alternator and battery).

Thanks

Jim

Reply to
Jim Ingram

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