Alternator testing

[richy759]

After changing my battery, I found it flat again the other morning (after driving it up to Bradford from Southampton). I had to call out the RAC to jump it and the guy came to the conclusion the alternator could be on its way out and was discharging the battery through it.
I have measured the current draw from the battery when idle which is about 500mA, i'm sure this is more than it should be.

Is there an easy way to test an alternator for leakage?
I have thought of 2 ways

1. Disconnect the output from the alternator (which goes to the battery positive terminal) and test current draw.
The Bible is strongly against this as there is high probability of grounding the live wire.

2. Disconnect the 100A fuse and test the current draw.
Agro...

I am not sure if there is an easier way, has anyone had to do this?
Edit: oh yeah, the 100A fuse it fine

Cheers,
Rich

Edited by richy759 on Saturday 18th August 13:22

[GreenV8S]

An inductive meter won't be sensitive enough for that so yes, you need to disconnect the main power lead at the alternator or at the battery. If you know what you're doing and are careful this can be done safely. If you don't/aren't then get somebody else to do it.

[spend]

Some cars have the fusebox wired thru the alt tho, so if you disconnect the alt or fuse there is only the starter left with any power. If there are 2 brown wires to alt, it should be OK, but if there are 4 you will need to keep them joined (away from the alt).

Dave

[richy759]

spend said:

Some cars have the fusebox wired thru the alt tho, so if you disconnect the alt or fuse there is only the starter left with any power...

If this was the case, if the 100A fuse was broken, it would power down almost everything wouldn't it?
I'm not sure what you mean about keeping the wires joined away from the alternator, are you suggesting disconnecting them and joining them to see if this stops the leakage?
I don't know how many wires my alt has coming off it (I think its a a127-100), i'll have a look later.
I think i'd prefer to go the 100A fuse route rather than fiddling with live wires near the engine block.

Rich

Edited by richy759 on Sunday 19th August 12:58

[richy759]

It turned out not to be the alternator draining the battery, it was the courtesy light delay relay. I had a look at the internals and it looks a bit scorched.
I rang my local motor factors but they don't stock them, has anyone bought one off a web site?

Rich