Alternator money saver info. - bosche.

HERBIEMERCMAN

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hi everyone, i just learned the hard way about my bosche alternator failing
( or so i thought ).

when you get in your car and turn the key and the engine just turns over just once you think, **** a new battery needed. my old man taught me to never blame the battery untill you have checked.

1. with everything switched off what is the current drain ?
2. is the alternator charging ?
3. are all electrical connections secure ?

i applied my multimeter to the task and item 2 was the problem, with the engine switched off i had 12.4 volts, with the engine running the reading was unchanged.

so off to my local breakers yard and returned with a used alternator for £30.
took me four hours to remove old one and fit replacement, nearly everything is in the way so lots of parts have to come off.

started the engine and the standing voltage increased from 12.4 volts to 14.2 volts. job well done.

i was pleased with the £30 fix. as the cost of exchange alternators is £125. or £160 for a new one.

just out of interest i took my old alternator to a friend who is an auto electrician, specialising in recon alternators, he tested my old alternator and said it was giving 80% of it's specified output. he also pointed out that bosche alternators are generally good for 150,000 miles.

i told him about the testing i had done and the fact that my battery was discharged? he said the problem is simple when you know about it. he has experienced many instances where the commutator brushes start sticking with carbon dust in their slides, causing the brushes to make little or no contact with the copper segments, so you get little or no charge.everyone assumes the bridge rectifier has failed or the windings are shot.

just removing the alternator can loosen the carbon dust and then when tested, as in my situation, the alternator performs to specification, a good tap with a hammer would have probably resolved my problem.

the commutator assembly with carbon brushes etc. is only £20. so i now have a surplus alternator in perfect working order.

as they say in france nue vive von, ( we live and we learn ). herbiemercman.
 
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S.Speed

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Hi..
I have to say I find your posts very interesting...
I get the impression your mind works in a similar way to my own..
 

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The alternator is a 3 phase device, you cant have a situation of a 80% charge, as it is either charging or it is not.
Sure if the brushes are worn out or the slip rings worn down to far you may get an intermittent charge.

With no output from the alternator the charging lamp is normally on, with one of the 3 diodes fault, the charge lamp may be lit very dimly. Many do not notice when in this condition
 
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HERBIEMERCMAN

HERBIEMERCMAN

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hi malcolm, you are correct, it was just my way of interpreting the intermittant nature of the problem. your point about the indicator warning lamp on the dash display is a good one, and i think this was the situation i had. best wishes. ian.
 

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