Alternator testing advice

Hi

Ended up with a flat battery at the end of a days laning yesterday. The battery is only a few weeks old so thats not the problem. I know I could check the voltage at the battery with the engine running to see if the alternator is charging it but with a flat battery I can't do this at the moment.

I have taken the alternator off now, can anyone help me with advice on checking the alternator with it off the car & also wiring/connections on car\ alternator to see if everything is OK ?

Thanks.

you should have two big and one little spade connectors that plug into your alternator. with the alternator disconnected and the ignition on, you should have 12v on the small one.
you should have continuity between both large spades and +ve on your battery.

if the above is ok and the battery is good the alternator is nadgered, it would be worth double checking your battery as this is the time of year they allways fail, most tyre and exhaust places will load test it for free.

Thanks

I have tried the above checks and all seems to be OK with the wiring.

I am looking at the back of the alternator and there is another spade type connector besides the 2 big/1small that the wiring block goes into.

Is this an earth that wasn't connected ? or is it something else ?

Thanks

Fatboy11 said:

Thanks

I have tried the above checks and all seems to be OK with the wiring.

I am looking at the back of the alternator and there is another spade type connector besides the 2 big/1small that the wiring block goes into.

Is this an earth that wasn't connected ? or is it something else ?

Thanks

Click to expand...

not sure what the extra pin is. the earth is usually via the casing.

it wouldnt be unusual for the same part to fit multiple vehicles, so this pin though not used on your landy may be used on different vehicle fitted with the same alternator.
the only three connections you should have/use are the ones described earlyer.

Well I'm stumped now. The 3 spade connectors were good, fitted a new alternator this morning and still only get 12.6v when started

Any ideas ???

Cheers

Are yu getting 12v on the ickle exciter wire?

Fatboy11 said:

Thanks

I have tried the above checks and all seems to be OK with the wiring.

I am looking at the back of the alternator and there is another spade type connector besides the 2 big/1small that the wiring block goes into.

Is this an earth that wasn't connected ? or is it something else ?

Thanks

Click to expand...

Rev counter?

Are yu getting 12v on the ickle exciter wire?

Do you mean the small spade connector that goes to the alternator? If so then yes.

Check the earth from your battery negative lead to the engine

10/10 Discovery 1, cleaned up the battery to chassis earth strap and now got 14.25v on tick over.

Cheers mate.

Just wish I had realised the problem before buying a new alternator yesterday although it was only £37, wonder how long that will last then lol.

Thanks for all the good advice again.

glad you got it sorted out mate!

I have fitted a second earth strap straight from the negative terminal on the battery to the engine - helps with charging and starting

Should I still get 14v at the alternator output connector with bad earthing or would this be reduced ? Cheers.

Bad earthing will reduce the voltage!

You should be getting between 13.8V and 14.2V delivered from the alternator to the battery.

Thanks for the reply, what I'm trying to timeout is if the alternator is good but bad earthing probs then would I get 14vish at the alternator output plug even if it is less at the battery thus not charging ?

Cheers

Fatboy11 said:

Thanks for the reply, what I'm trying to timeout is if the alternator is good but bad earthing probs then would I get 14vish at the alternator output plug even if it is less at the battery thus not charging ?

Cheers

Click to expand...

Yes!

Check your earths!!

Obviously you have a multimeter?? The resistance between the engine and the battery should be less than 3 Ohms, with the same between the engine and chassis, engine and body, and everything and the battery negative terminal!!