Battery light on when stopped, off when running
Discussion
I think the alternator might be packing up, last night as soon as I stopped the car the alternator light came on. Then I found that it went off as soon as I turned on the ignition. Now it won't charge and the back end of the alternator was boiling hot after a 20 mile run.
Luckily I have a battery isolator so I could disconnect it easily after stopping.
Luckily I have a battery isolator so I could disconnect it easily after stopping.
Jack Valiant said:
Hi Adam
Light staying on is an indication of one or more diodes in the rectifier pack in the alternator are breaking down or have gone short circuit. Time for a replacement fella!
Chris
Yep, happened twice to me, second time I had the diodes replaced. Been fine since.Light staying on is an indication of one or more diodes in the rectifier pack in the alternator are breaking down or have gone short circuit. Time for a replacement fella!
Chris
Yeah I reckon that's the problem - it does put out some power from time to time - but it takes 3A off the battery with the engine stopped.
I have another with some dodgy bearings which might do for a few days while I replace the diodes.
I have another with some dodgy bearings which might do for a few days while I replace the diodes.
Edited by adam quantrill on Wednesday 7th March 22:22
Well the duff one turns out to be an A127 Lucas alternator. I can get a diode pack off ebay for 12 squids delivered so not too bad.
I put the old dodgy one on and it wouldn't output any current. I hummed and hahed and decided to drive to work anyway as I had charged the battery overnight and it was a nice day with no chance of rain.
Then I had a stoke of luck - about time too - after about 5 miles the voltmeter suddenly came up to 13V and the battery light went out - it's charging! Not bad from an old alternator which has been sitting in the barn for 10 years. I reckon the field brushes eventually cleaned up the rings and it all started working. The battery light comes on dim on idle but beggars can't be chosers ;^)
I put the old dodgy one on and it wouldn't output any current. I hummed and hahed and decided to drive to work anyway as I had charged the battery overnight and it was a nice day with no chance of rain.
Then I had a stoke of luck - about time too - after about 5 miles the voltmeter suddenly came up to 13V and the battery light went out - it's charging! Not bad from an old alternator which has been sitting in the barn for 10 years. I reckon the field brushes eventually cleaned up the rings and it all started working. The battery light comes on dim on idle but beggars can't be chosers ;^)
Got the back off the original alternator - 3 out of 6 diodes are shot. Ordered a replacement off fBay for 11 quid (even better) just 3 solder joints and 8 bolts and it's back together. Plus some grease in the bearings while it's opened up. The dodgy one is holding up nicely so should be good for another week then it can go back in the barn for another rest on the shelf....
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