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Certifiable BMW Whackjob!
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Discussion Starter #1 (Edited)
So after a string of brain farts I stupidly blew out my alternator. Killing the battery is how I killed the alternator so I replaced it since I wasn't sure exactly how old it was (5 or 6 years depending on country sticker was printed). With the new battery the voltage measures 12.2-ish regardless of whether the car was off or running at any RPM, and so I believe it was my stupidity that killed the alternator when I jumped it and didn't turn anything on before yanking the cables off (after 1AM Friday night trying to leave work).

Now being the cheapskate that I am (this is the most expensive year I've had since buying the house and that doesn't include this car) I figured I'd just replace the likely bad electronics for a couple bucks instead of the whole alternator for hundreds of bucks. I also wanted to see if this could be done without actually removing the alternator and having to mess around with the coolant.

So according to Timm's alternator rebuild (his focuses on replacing the bearings) it should just take a couple of clouts to get the 24mm nut off...maybe it was because of the location while still mounted in the car but I had to order tools and do it the right way. While a 24mm socket fits nicely on the nut, since I needed to get a tool into the shaft I ordered a deep offset 24mm box wrench - which I then needed to grind down the OD of so it would fit inside the pulley. And to hold the shaft I ordered a set of spline bits (aka triple square), I tried using torx bits but they wouldn't hold being only 6 point and sized differently - it is a 12 point M10. Once the nut is off the pulley slides right off then you remove the connector and the battery cable (17mm), the nut under the battery cable (15mm), the 4 torx screws (T25) and...the cover is almost ready to come off. One of the pulleys on the tensioner needs to come off and then you just slowly pry the cover off as the seal peels apart.

Now that the cover is off there is just a few torx screws (T20) to remove the regulator (currently available on eBay from $15-50 from many sources). This is where my questions start...
Is there a wiring diagram of the alternator itself so I can make a test procedure for the regulator by itself? Or is there already one that I have been unable to find? The battery terminal is the obvious connection, what are the 2 wires in the plastic connector for (blue=field voltage and...)? As for the diodes, in the 7th picture of Timm's rebuild it is shown in pieces but I assume to get it that far you actually have to remove it, so can just the plastic piece attached to all the diodes be removed easily (looks like 6 screws if it isn't soldered to the diodes)? Does anyone have a picture of the back side of that piece that shows the other end of the diodes?

NOTE: I took it apart on Saturday so tool sizes are from my shoddy memory, I'll correct any errors when I put it back together. Hopefully I also remember to take some pictures.

Tool list summary:
24mm deep offset box wrench = alternator pulley nut
M10 spline aka triple square = alternator shaft
T50 torx bit = tensioner pulley (slightly in front of cover)
T20 torx bit = regulator & diode bridge
17mm socket = battery terminal top nut (to remove battery connection) & tensioner nut (pre-tension the belt)
15mm socket = battery terminal bottom nut (to remove cover)
13mm socket = tensioner bolts (the belt)
and the various tools to remove the fan, shroud and everything in the way of removing the shroud (air box, MAF, engine cover...)
 

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Certifiable BMW Whackjob!
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5,982 Posts
Discussion Starter #3 (Edited)
Regulator was only $14.99, perhaps in my really long post (sorry about that) you missed the part where I said I was trying to be cheap.

Spending a lot of money this year:
Washer/dryer (February) = $1600
Wife got a smartphone (March) = $$$
Garbage disposal (April) = $200
Daughter got a smartphone (May) = $$$
Nephews wedding (June) = $3000+ (3 days in Indiana, cargo box, nice clothes for all the kids...)
Chromebooks (September) = $900 (new program at school requires deposit [3 x $300])
Paycut (September) = -7% (switching from second to first shift)

I'm guessing I'll need about $10K to finish my backyard and that doesn't include the $3000 I'll need for the pool in the spring. I also have a project E46 330xi in the garage I need to buy parts for and hopefully if I can get the garage door fixed ($$$) so it's more than 20° in there I can work on the E38 while it's parked this winter (gas tank, brakes, suspension, fluid changes, etc.).

So you see, sometimes you have to try to save money where you can - even if it's just $210.
 

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Regulator was only $14.99, perhaps in my really long post (sorry about that) you missed the part where I said I was trying to be cheap.

Spending a lot of money this year:
Washer/dryer (February) = $1600
Wife got a smartphone (March) = $$$
Garbage disposal (April) = $200
Daughter got a smartphone (May) = $$$
Nephews wedding (June) = $3000+ (3 days in Indiana, cargo box, nice clothes for all the kids...)
Chromebooks (September) = $900 (new program at school requires deposit [3 x $300])
Paycut (September) = -7% (switching from second to first shift)

I'm guessing I'll need about $10K to finish my backyard and that doesn't include the $3000 I'll need for the pool in the spring. I also have a project E46 330xi in the garage I need to buy parts for and hopefully if I can get the garage door fixed ($$$) so it's more than 20° in there I can work on the E38 while it's parked this winter (gas tank, brakes, suspension, fluid changes, etc.).

So you see, sometimes you have to try to save money where you can - even if it's just $210.
Yep I have had those years before. know exactly what you mean. Last year was a bad year. It will turn around for you. best wishes
 

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Certifiable BMW Whackjob!
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Discussion Starter #5 (Edited)
Found a couple of things so far...
So here is my guess: B+ is direct battery connection, G is ground, F gives power to the field (since it is brushless), Ps is the power generated by the other coils after it has gone through all the diodes, IG is 12V from the ignition and L is the output to turn on the warning light.
 

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Certifiable BMW Whackjob!
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Discussion Starter #6
Wow, nobodies got anything?

So here is what I did so far (3 power supplies and a scope):
12V on "IG"
12V through a resistor to "B+" (need resistor to "absorb" charging voltage)
0-20V to "Ps"
All grounds tied together going to "G"

Scoping "F" shows a 5V square wave with about 90% duty cycle (removing 12V from "IG" or "B+" kills this signal)
Still waiting for my new regulator so I used what I assume is my bad one and...voltage on "B+" never changes regardless of voltage applied to "Ps" so it doesn't look like it will charge a battery which is my problem. Looks like it really is bad.

Still left with a question though about the "L" connection. Is that to turn on the dash light? Should it be high or low because my light was on but no matter what I did during the test it never left ground.
 

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Did you consider starting by replacing the voltage regulator?

Wife's E46 330Ci was showing just 11.9v at the battery with engine running. The regulator is a lot cheaper than an alternator, so replaced that as a first step and problem solved. The brushes on the old regulator were about half the length of the new ones, and the commutator needed cleaning too. Now shows 14v+.

Apart from bearings, alternators themselves don't often fail...
 

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Certifiable BMW Whackjob!
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5,982 Posts
Discussion Starter #8
Did you consider starting by replacing the voltage regulator?

Wife's E46 330Ci was showing just 11.9v at the battery with engine running. The regulator is a lot cheaper than an alternator, so replaced that as a first step and problem solved. The brushes on the old regulator were about half the length of the new ones, and the commutator needed cleaning too. Now shows 14v+.

Apart from bearings, alternators themselves don't often fail...
Oh crap! How did I miss your reply?

One of these days I'll get around to ripping the old alternator apart and coming up with a way to test the parts without removing it from the car and finish this thread, but yes I started by replacing the regulator and when that didn't solve it I went ahead and replaced the alternator. I'm exceptionally unhappy with the eBay seller because of shipping issues but months later it is still working.
 
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