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voltage regulator stuff

Posted by jaffar 
June 13, 2011 09:55AM
hi all

long time, no see smiling smiley

just wanted to share with you a funny little story about what i did yesterday.
after having a nice drive for 2 days on mountain roads and being very happy that my old e36 is still in good shape, on the road back, i saw a nice red light in the dashboard, with the shape of a battery. it was not "completely" lit (like when you turn the key, before starting the engine), but just barely.

i thought "oh, well, the battery is 5 years old, it's about time". problem - it was sunday, and next day was a national holiday and i was in the mountains smiling smiley
so i decided to turn everything off (lights, air cond, stereo, gps power etc.) to save power and i drove as fast as i could. i heard some rumours before, that in such a case, you can drive off a full battery for about 3 hours, so perfect time to verify the theory.

i drove exactly 2h50m before the engine stopped. guess where - right on a railway crossing smiling smiley and 3 km away from the resting place (which included a fully equipped garage).
i pushed the car back from the railway, took the battery to the garage and tried to charge it. of course, being too empty, the charger was overheating and pausing very often. i let it charge over the night and tried to start the car in the morning. i was able to drive the last 3 km and took the alternator out.

to my little surprise, the alternator coals were finished. well, not both of them, but just one. exactly like it happened on my e30 several years ago, only one of the coals was completely eaten, and it took the rotor contacts with it, too.

that's the point where i started to hate BMW and Bosch again - why the hell they don't allow us to just replace the coals for $1, but they force us to buy a new regulator for $200 !? stupid engineers.. or salesmen..

so, what to do, considering there are no parts to buy on the spot, and i was still about 220km from home ?

now the most funny part - my friend (the garage owner) had an old e28 alternator with two pretty good coals. of course, Bosch made it impossible to replace them, but guess what mad idea we got ? since my broken coal was almost completely worn off, i could push it in all the way, and still had about 5 mm spare. so i cut one of the e28 coals, grinded it to shape and put it OVER my used coal. mechanically, it works perfectly. electrically... let's see.

we put everything back together... turned the key... and IT WORKS ! no red battery light, voltage back to 14.4v, battery charging, all lights on, everything works. it was good enough to bring the car back home, and possible to drive for several more years.

of course, now i need to think what to do:

- buy new regulator with new coals (but the rotor is also damaged - although i saw this kind of damaged rotor still work for years after replacing the coals)
- buy new alternator - way too expensive for a stupid coal
- just drive and forget about it, until it breaks again

the conclusion - you can drive for almost 3 hours without an alternator, but without any lights, too smiling smiley

A physics truck just turned over outside. There's physics everywhere!
June 13, 2011 11:54AM
If it was my car, I would buy another used alternator, have the coal brushes and the regulator replaced, and replace the thing for peace of mind.
As you know now, when the alternator quits and battery runs out, the car stays where it is, is that kind of thing.
Also a bad regulator can fry your battery, which recently turned to be much more expensive than they used to.
In the mean time, having a cheap battery charger to recharge your battery at home is a good idea, specially in the winter and cold climate.

Best regards,
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