Is your alternator "on its way out" or already dead? If so it is highly possible that the alternator itself is fine and the problem lies in the voltage regulator. This is a guide to replacing the two graphite brushes that are on the voltage regulator of your Bosch alternator. I have never dealt with an e30 with the Valeo alternator, so I can't provide any guidance with that. I do know that the Valeo unit does not have a voltage regulator that external and easily removable like on the Bosch units.
A quick lesson: The voltage regulator supplies current to the rotor winding in the alternator through the graphite brushes and slip rings. It uses the field current as supply. The regulator also has a control voltage input from the battery. If battery voltage drops, the regulator increases the field current supplied to the rotor. The strength of the magnetic field then increases and as a result, alternator output voltage increases. And if a voltage increase at the battery is sensed, the regulator will retard the field current that it passes to the rotor. If your brushes are worn past their functional point, the rotor will be spinning around in there without a magnetic field to induce current in the stator.
I have had an alternator fail on me before more than once, and usually a failing alternator will exhibit some tell-tale signs like a noticeably sluggish starter, strange behaving electronics, etc. In an e30, you will also be warned by the battery light on the instrument cluster. This most recent time, I did not experience any of the normal issues that I associate with a bad alternator. I got in my car to go home from work, it started up normally and then a few of the dash lights were lit, but dimly as seen here:
They were definitely not illuminated fully. There were no other symptoms for about 20 minutes and then my deck started turning on and off rapidly. I knew that there was an electrical issue, and I was convinced that is was a charging system issue. When I got home I put my multimeter on the battery while idling and I could see that the alternator was outputting about 11.0V. So I pulled the alternator, and then the voltage regulator. I then saw what I though was my issue. The brushes were about 5mm and 3mm respectively. The Bentley manual says that the brushes are 12mm new and should be replaced at 5mm. So I set out to get some new brushes.
I should note right now that rather than replacing the brushes, you might just rather replace the entire voltage regulator. I was quoted $90 for a remanufactured alternator, $104 for a new voltage regulator and $3.49 for two new brushes at O’Reilly Auto Parts. I do not like buying my parts there, but I needed to get this fixed immediately, so I went for the brushes. I have since learned that you can get a new voltage regulator for around $25-$30 if you buy it online.
Anyways, on to the fun part. Once you have the voltage regulator removed, you need to remove the solder from the two areas where the brushes are attached. You don’t need to spend too much time with the solder sucker, you just need to clear it out of the way so you can open up the crimped part that holds the brush in. You can see here I have one of the brushes removed. When you have the solder cleared, carefully pinch open the crimp. The brush with then come out along with the spring behind it.
Do the same for the other brush. Be sure to be careful when opening the crimp, or you will just pinch it more closed as I did on the second one. I ended up having to get a small drill (I think I used a 1/32” bit) to open it up.
You can then install the new brushes. They come with an inch or two of wire lead. With the spring in, run the wire through the hole, and compress the spring with the brush so that 12mm is exposed. Hold it in place there and crimp the hole closed to secure the brush there.
Do this for both brushes, and then solder the crimped area to ensure that there is good conduction going on there. Go ahead and trim the excess lead off too. Here is one of the brushes done:
And both:
Now you’re good to go. Install the voltage regulator back in the alternator and put the alternator back in the car. Make sure you charge the battery in the car while you are doing all of this. Start the car up and put your multimeter across the battery terminals to test the alternator output.
Easy enough, right?
A quick lesson: The voltage regulator supplies current to the rotor winding in the alternator through the graphite brushes and slip rings. It uses the field current as supply. The regulator also has a control voltage input from the battery. If battery voltage drops, the regulator increases the field current supplied to the rotor. The strength of the magnetic field then increases and as a result, alternator output voltage increases. And if a voltage increase at the battery is sensed, the regulator will retard the field current that it passes to the rotor. If your brushes are worn past their functional point, the rotor will be spinning around in there without a magnetic field to induce current in the stator.
I have had an alternator fail on me before more than once, and usually a failing alternator will exhibit some tell-tale signs like a noticeably sluggish starter, strange behaving electronics, etc. In an e30, you will also be warned by the battery light on the instrument cluster. This most recent time, I did not experience any of the normal issues that I associate with a bad alternator. I got in my car to go home from work, it started up normally and then a few of the dash lights were lit, but dimly as seen here:
They were definitely not illuminated fully. There were no other symptoms for about 20 minutes and then my deck started turning on and off rapidly. I knew that there was an electrical issue, and I was convinced that is was a charging system issue. When I got home I put my multimeter on the battery while idling and I could see that the alternator was outputting about 11.0V. So I pulled the alternator, and then the voltage regulator. I then saw what I though was my issue. The brushes were about 5mm and 3mm respectively. The Bentley manual says that the brushes are 12mm new and should be replaced at 5mm. So I set out to get some new brushes.
I should note right now that rather than replacing the brushes, you might just rather replace the entire voltage regulator. I was quoted $90 for a remanufactured alternator, $104 for a new voltage regulator and $3.49 for two new brushes at O’Reilly Auto Parts. I do not like buying my parts there, but I needed to get this fixed immediately, so I went for the brushes. I have since learned that you can get a new voltage regulator for around $25-$30 if you buy it online.
Anyways, on to the fun part. Once you have the voltage regulator removed, you need to remove the solder from the two areas where the brushes are attached. You don’t need to spend too much time with the solder sucker, you just need to clear it out of the way so you can open up the crimped part that holds the brush in. You can see here I have one of the brushes removed. When you have the solder cleared, carefully pinch open the crimp. The brush with then come out along with the spring behind it.
Do the same for the other brush. Be sure to be careful when opening the crimp, or you will just pinch it more closed as I did on the second one. I ended up having to get a small drill (I think I used a 1/32” bit) to open it up.
You can then install the new brushes. They come with an inch or two of wire lead. With the spring in, run the wire through the hole, and compress the spring with the brush so that 12mm is exposed. Hold it in place there and crimp the hole closed to secure the brush there.
Do this for both brushes, and then solder the crimped area to ensure that there is good conduction going on there. Go ahead and trim the excess lead off too. Here is one of the brushes done:
And both:
Now you’re good to go. Install the voltage regulator back in the alternator and put the alternator back in the car. Make sure you charge the battery in the car while you are doing all of this. Start the car up and put your multimeter across the battery terminals to test the alternator output.
Easy enough, right?
and resoldered the brushes in 3 minutes tops. Kinda shoddy if you asked me. But for RM20($6.50), i really can't complain.
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