hey guys this is Harry.recently the dynamo in my E36 318 fried.got a second hand one which the dealer said was working . but when i connected all the wires and started the engine,check battery light was still on.is there a way to know if my new alternator is working?how much voltage shud a good alternator give at idling .i returned the new one and dealer says one of the IC s inside the alternator had fried and this cud have happened when i set it up. is there any precautions to be taken when fixing new alternator other than removing minus battery wire?i m totally lost.

Voltage across the battery terminals should be about 13.5 V with the car running. About 12.5 V with the car off. Autozone stores usually have a machine that will test the battery with a load and check the alternator output.

BTW, the IC in the alternator is the voltage regulator and a rectifier. If you put power across it in the wrong direction, it will ruin the diodes in the circuit that changes the alternator output from AC to DC.

Disconnecting the battery while the car is running will also destroy diodes.

Chances are, its your voltage regulator that's bad. I just replaced one , it cost about $85 and the alternator works like new.

put a voltmeter across the leads of the alternator ... what better way to check if it's working? (of course, only connect it while it is not running, and set your meter to handle high amperage if applicable)

got another alternator ,got the battery charged.when i started engine at first the check battery light was off.voltage across battery was around 14V.then i took the car for a little ride and 30 mins later check battery light started coming on especially when i accelerated.after a few mins engine died.checked the voltage across battery after jump starting and this time it was below 12V with engine running.theres a burning smell from under the hood.had i cooked my third alternator?why do bmws have so many electrical problems.

mine never had this problem. but btw i think i was out of it when i said to measure the voltage across the alternator when it is not running ...

sorry about that lol :blush2

Maybe faulty grounding or short somewhere?