Alternator problem

YellowVanMan

have a 2000 mitsu spacewagon 2.0 glxi(4g63) that wont charge the batt. brought to the rewinds and he says the alt is fine. put it back in the car and checked all connections, they are all fine.

when it is running at idle speed you can turn on all lights, fan, wipers and no battery light comes on, but as soon as i rev it up the battery light comes on and stays on, the yellow oil light(not the red one) comes on also.

i have over 12v at the battery + and -, over 12v at the alt + and -, alt fuse is not blown.

any ideas what could be wrong.

namoosh

Should be around 13.5 volts at the alternator and battery with engine running. Loose fanbelt, worn bearing on alternator, faulty voltage regulator?

YellowVanMan

thats the voltage before running. it drops to 11.7 and so on when running coz of plugs and accessories etc.

YellowVanMan

anyone know how to test the rectifier, i'm not much of an auto elec so gratefull for all advice.

joujoujou

Check how voltage changes while you're revving up.

It may be faulty voltage regulator or one (or more) of diodes died.

jimmyw

Possibly a loose connection somewhere causing a high resistance in the circuit.

If you got the Alternator tested, shouldn't any faults such as the rectifier, brushes,windings etc have come up while testing? Unless it only occurs when under load.I don't know how it was tested by the repairer, whether under load or not.

You shouldn't be driving it if the oil light is on to be sure, although I don't know exactly what that one you mention is for.Does it have two oil lights? Though it may be only an electrical fault with that.

YellowVanMan

it was tested at the rewinds place. doesn't change voltage when revved up.

jimmyw

YellowVanMan wrote: »

it was tested at the rewinds place. doesn't change voltage when revved up.

Well that not right, I'd say it is faulty.You need to know what that voltage is.

YellowVanMan

could there be a faulty wire from the rectifier?

jimmyw

The tester should have ruled out any faults with the alternator.So I dont know if they tested it properly if at all.So I'd say either go back to them or else try somewhere else.

YellowVanMan

ok, here's the update.
rechecked all the terminals and earths for voltage, to me everything seemed ok so i took out the alt again and brought it to another rewinds man... same result again, "nothing wrong with that alternator".

home, refit alt, and check everything again. i'm certain that the main wires and earths are ok, so i started to go back beyond the fuses and engine bay wiring. under the dash i found a bunch of piggyback wiring used for a phone kit or something, a right mess of black wire and insulation tape and accessory fuses.

hoping my problem lies somewhere beneath this mess.


jimmyw--- yep, it has two oil lights, a level and a pressure light. the yellow one is the level light(it's fine for oil).
the oil level light wire runs parallel with the rectifier wires, and it comes on exactly when the battery light comes on every time.

anyhow, i'll keep ye posted just incase ye ever experience the same problem.
thanks lads

jimmyw

Dear oh dear! I think you need to work on the battery light circuit.Did you say what voltage your getting across the battery when its running?

You should be getting over 13 volts even with the engine at idle.If you take off the wire from the light at the alternator, the light should not be on the dash.If it is, then its earthing somewhere that it shouldn't be.

Some alternators use the batt light circuit to "excite" (feed in a small current to start off charging of the alt) while some use a different wire I think.

I am not sure about that wire to the rectifier? The rectifier wiring should be internal in the alternator, not on the outside.

YellowVanMan

the voltage across the battery is 12.4 and gradually gets lower. there is no difference when running except for the draw on the battery from the car.

i was thinking the wires coming from the rectifier to the dash/ignition might have some break or fault/earthing.

DublinDilbert

I'm not too familiar with this model, but I would check the supply to the voltage regulator on the alternator...

YellowVanMan

the supply to the volt reg is the same as what ever is in the battery at the time. it comes from the ignition. the other one goes to the batt light.

jimmyw

YellowVanMan wrote: »

the voltage across the battery is 12.4 and gradually gets lower. there is no difference when running except for the draw on the battery from the car.

i was thinking the wires coming from the rectifier to the dash/ignition might have some break or fault/earthing.

That voltage is definitely not right.Have a play around with the two other wires, i.e batt light wire and other wire.It sounds to me on your model, the feed to the voltage reg (excite) is separate from the batt light.

HellFireClub

YellowVanMan wrote: »

anyone know how to test the rectifier, i'm not much of an auto elec so gratefull for all advice.

A general rule of thumb is that with the engine running, you should be getting above 13.5 VDC across the battery terminals with the engine running. If you are not getting a value that is in between 13.5 VDC and 14.0 VDC then generally you have an alternator problem.