How to measure alternator output?

[DaveR]

Red battery light came on today 60 miles from home. I'd been driving for 90 mins at that point which seemed a bit odd.

Went to my meeting, came out, car started fine. No battery light. 20 mins later. Battery light comes on again.

Power ultimately lost and I stop. Battery looks to be the original (so 10yrs old) and is clearly leaking. I figure it doesn't owe me anything having lasted that long so replace it with a new sealed unit.

Car starts perfectly but red battery light on again on dash. In case the new one's been on the shelf for a while I've just put the charger on (which is indicating that it's a bit depleted).

How do I measure the alternator output though? Obviously this could still be the issue and I'd prefer to establish if the battery is being charged when the engine is running without waiting to get stuck at the roadside somewhere.

Thanks in advance...

Dave.

[E30M3SE]

Connect a multimeter set to volts across the battry, red to '+' black to '-', start the car and rev to circa 2K, the multimeter should read between 13.5 and 14.4 volts, anything less and the alternator is not charging sufficently, anything less than 12V and it's donald ducked.

[phelix]

What he said - also good to see what happens when loads are switched on such as the main beams, AC/heating blower and rear demister. Voltage measured at the battery should be close to constant if the alternator is doing its thing.

[DaveR]

Thanks for your input chaps. 12.0V engine off. 12.0V engne on... at any rpm. B*gger.

With what little daylight there was, I could see the alternator belt and the drive wheel on the front of the alternator spinning nicely and the rotor stood stock still. I think he's gone to the great yard in the sky.

Anyway, the car's down at the local garage now. I feel a bit guilty as I'm sure it's a fairly simple job to whip off the airbox, undo a couple of bolts, a few persuasive taps with a mallet etc. but I'm supposed to be working...

Thanks again,

Dave.

[8Tech]

Thats not the alternator, just the pulley clutch. MUCH cheaper.

8Tech.