[dimitriseas]

hello friends . i am from Greece . sorry for my english , i want to ask if that voltage it normal to measure to my car. the polymeter give me 15.4v and also the diagnostic (delphi) give me the same value.. do you have any solutions before to burn all my modules. thanks

[charlie_m]

There is nothing wrong with your English! (Except polymeter is better translated as 'multimeter' ... took me a little time to find what you meant). In any case it is good that you checked the voltage with a separate meter.

My first thought is a bad voltage regulator on the alternator. You can replace the entire alternator or try just replacing the voltage regulator (check to be sure it's the right part number):
https://www.ecstuning.com/Search/Sit...h/12317561939/

Also check your chassis grounds and power cables. Not as likely, but it may be that a bad or failing connection (causing increased resistance) is making the alternator push out higher voltage to reach the target charging current. Grounding straps are known to corrode, and power lugs are known to have bad connections even though they look fine.

Changing the voltage regulator is pretty easy, but attached is a PDF showing the procedure. Bosch and Valeo are slightly different.

[dimitriseas]

thank you for your help ... i already have buy one used alternator (incl. regulator) and i will replace it by myself, that need to disconnect the battery of cource. what else must to be carefull doing that job?

[charlie_m]

Check the belt condition and tensioner pulley condition, now is a good time to replace them if needed. The manual calls for the (4) bolts to be replaced also.

Here is a detailed walk-through:
https://www.pelicanparts.com/BMW/tec...eplacement.htm

[e91Owner]

You may also just want to swap the voltage regulator from the new alternator to the old one. It's very easy and you can always save the new alternator for a later time.

[dimitriseas]

am here again after new data... Finally i change all the alternator and my problem solved. I see 14.5v now. BUT.
my new alternator is 150ah (#7799180) and my old 180ah (#8507624) is that problem? I let that alternator now because i don't want to fried any module.

[e91Owner]

Originally Posted by dimitriseas

am here again after new data... Finally i change all the alternator and my problem solved. I see 14.5v now. BUT.
my new alternator is 150ah (#7799180) and my old 180ah (#8507624) is that problem? I let that alternator now because i don't want to fried any module.

Not sure what car you have, but most original alternators are either 170 or 180A. Old 318d's had 150A.

You're probably fine regarding the alternator output, but I would be more concerned about the actual dimensions of the alternator and pulley size affecting the tension on the belt.

However, only you can tell if that output is sufficient for your car.

[dimitriseas]

Thanks again. The pulley size is the same. What do you mean. How understand is that 150ah is enough for my car. How to check that

[charlie_m]

Originally Posted by dimitriseas

How understand is that 150ah is enough for my car. How to check that

Check that the alternator can keep up charging voltage (like 13.5V ?) when the car is running with high electrical loads (like high beam headlights on, fog lights on, inside fan on high, etc at the same time). Some loads you cannot check, like a battery that is going bad and needs a lot of charging.

So, keep an eye on charging voltage as your battery gets older too. In my vehicles I usually keep a small voltmeter plugged into the 12V power outlets to monitor charging voltage.

[dimitriseas]

Nice idea . I have diagnostic tool (delphi) i can watch real time the charging procedure. And with lights open..

[e91Owner]

Originally Posted by charlie_m

Check that the alternator can keep up charging voltage (like 13.5V ?) when the car is running with high electrical loads (like high beam headlights on, fog lights on, inside fan on high, etc at the same time). Some loads you cannot check, like a battery that is going bad and needs a lot of charging.

So, keep an eye on charging voltage as your battery gets older too. In my vehicles I usually keep a small voltmeter plugged into the 12V power outlets to monitor charging voltage.

This is not correct.

The only way to see if the 150A alternator is meeting the demands when a 180A alternator is the normal rated alternator is to measure current, not voltage.

I have no idea what this would be called in Greek, but in English you would place an Amp clamp on the + wire from the alternator and measure peak current with all of the accessories on. As long as that is roughly 130A or less (it certainly should be), it's fine.

[dimitriseas]

Understant what you mean. We call that Amper meter. I Will try to find the way how to do that. Thank you

[e91Owner]

Originally Posted by dimitriseas

Understant what you mean. We call that Amper meter. I Will try to find the way how to do that. Thank you

It is an Ammeter, but it looks like a clamp. The one in the photo only measures AC current, but would look like this.

[dimitriseas]

A ha . I thinking that you mean the multimeter setting at ohm resistance. This is another thing

[charlie_m]

Originally Posted by e91Owner

This is not correct.

The only way to see if the 150A alternator is meeting the demands when a 180A alternator is the normal rated alternator is to measure current, not voltage.

Well, let's agree to disagree!

An ammeter can provide some insight, but alternators are controlled and regulated by voltage output. Field current determines alternator output level, and the voltage regulator controls field current based on observed voltage.

I maintain that an under-sized alternator would not be able to put out full charging voltage when full power is called for. You can 'call for full power' by either turning on all accessory power loads, or by 'full fielding' the alternator manually. There are tons of references where high-power audio installs overwhelm the stock alternator, and the symptom is always insufficient voltage.

But, you may disagree.

[e91Owner]

Originally Posted by charlie_m

Well, let's agree to disagree!

An ammeter can provide some insight, but alternators are controlled and regulated by voltage output. Field current determines alternator output level, and the voltage regulator controls field current based on observed voltage.

I maintain that an under-sized alternator would not be able to put out full charging voltage when full power is called for. You can 'call for full power' by either turning on all accessory power loads, or by 'full fielding' the alternator manually. There are tons of references where high-power audio installs overwhelm the stock alternator, and the symptom is always insufficient voltage.

But, you may disagree.

Yes, most of what you said is a misunderstanding of basic circuits in a voltage regulated field.