Alternator Whine

[jackwdwyer 10+ year member]

Hi, ive just installed a second amp to my 1992 BMW 325. I still have the factory alternator. The alternator has started whining since, and i was just wondering what effect this has on the car apart from making a funny noise. Will it harm the alternator or cause the car to run any differently? any advise would be appreiciated. Thanks, Jack.

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[helotaxi 5,000+ posts]

It has nothing to do with the alternator.

 

[jackwdwyer 10+ year member]

have you got any idea what the problem is then?

 

[sdmtnbiker420 10+ year member]

its probably ground loop.

 

[jackwdwyer 10+ year member]

oh, ok, the noise gets higher pitched and louder with higher revs, is that what ground loop does?

 

[jackwdwyer 10+ year member]

thanks for the replies, have just seen the sticky about ground loops, will read up on it. thanks, Jack

 

[helotaxi 5,000+ posts]

It is caused by a ground differential between the source unit and the amp. Chances are that your HU ground isn't as good as it should be.

It is called alt whine because the sound you hear is the voltage ripple coming off the rectifier on the alt. The freq changes with RPM because the alt spins quicker.

 

[sdmtnbiker420 10+ year member]

Where is your head unit grounded to?

 

[jackwdwyer 10+ year member]

My headunit is grounded to the stock location. Should i run a new ground to somewhere that i know is good? Are there any preferable locations to ground a headunit? Jack.

 

[helotaxi 5,000+ posts]

Find a screw that goes into the sheetmetal of the car behind the dash. Sand the paint off around that screw and use it as the ground point.

Did the BMWs have designated ground points back then? I'm pretty sure that they do now. If that's the case, use a section of 12ga wire to extend the ground to one of the ground points if needed. There should be one behind the dash.

 

[sdmtnbiker420 10+ year member]

REad the 10 commandments of Noise Prevention

http://www.termpro.com/articles/noise.html

one of them is "never ground a head unit to the stock wire.

 

[jackwdwyer 10+ year member]

Thanks for the help and the link, will read that now. Jack

 

[helotaxi 5,000+ posts]

That article was written in 1989 and is full of mythical information. In fact several of the DO NOTS in that article have been found to be DOs to fix noise issues.