Alternator Voltages

[Quarryman 1]

I think i might have disturbed the alternator wiring. After running the car for a few minutes and trying to restart it wouldn't turn over again. A jump start fixed it straight away. Then dead again after a few minutes running.

 

How can i check if the battery is being charged by the alternator? Where can i check the voltages and what should they be?

[Tom Fenton 1,542]

Check the voltage first at the battery with the engine stopped. Hopefully you will have aomewhere between 12-12.5v.

 

Then start the engine and check again, you should now see something like 13.5 - 14v indicating the alternator is charging.

[pablo 0]

Try giving it a little rev once you jump start it. My old pinto used to read 12v when idling after being started until it got a little blip then went up to high 13s and stayed there.

Edited November 12, 2009 by pablo

[Quarryman 1]

Check the voltage first at the battery with the engine stopped. Hopefully you will have aomewhere between 12-12.5v.

 

Then start the engine and check again, you should now see something like 13.5 - 14v indicating the alternator is charging.

 

 

great, that's what i needed thanks.

 

That f**kin multiplug. I re-wired some it to try fix the starter problem. It didn't fix it and now the battery does not seem to be getting charged so I'm thinking i might have disturbed the alternator wire.

 

What happens if the wire from the multiplug is un-connected? I assume it just doesn't work and gives the symptoms i'm seeing?

[jackherer 543]

What happens if the wire from the multiplug is un-connected? I assume it just doesn't work and gives the symptoms i'm seeing?

 

Yes, the battery light on the dash should come on when you turn the ignition on then go off with the engine running. With that wire disconnected you will never see the battery light come on and the alternator wont start charging unless you rev the engine beyond 2 or 3k.

[Quarryman 1]

Yes, the battery light on the dash should come on when you turn the ignition on then go off with the engine running. With that wire disconnected you will never see the battery light come on and the alternator wont start charging unless you rev the engine beyond 2 or 3k.

 

thanks, i'll check for the battery light.

 

just to clarify above, the alternator won't start charging until the engine revs beyond 2-3k in all situations or in the 'broken' state (ie no battery light)?

[welshpug 1,657]

in the broken state, when its working it'll charge from the second the engine turns

[Quarryman 1]

in the broken state, when its working it'll charge from the second the engine turns

 

that's interesting.

 

What is the reasoning behind that behaviour. Does it switch off the alternator with this wire depending on a current reading from the battery (ie its fully charged)?

 

apologies for the simple questions, i'm not too up on the workings of the alternator.

[Tom Fenton 1,542]

The alternator requires an exciter current to start it working. This in very basic terms is linked to the battery light on the dash. Once the alternator is excited it will charge away happily. If the exciter current is not there, by about 3000rpm engine speed (6000rpm alternator speed) it is excited enough to start charging anyway.

[Cameron 16]

Exciting stuff. (Ohhhhhhhhhhhhhhh!!!)

 

Always wondered why my alt would never charge until I blipped it over about 1.5Krpm, now I know.

Guess I should extend my exciter wire then.

[Quarryman 1]

Thanks guys. Replaced the wiring to the alternator and all is well.