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E90 Alternator Field/Excite Wire?
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06-20-2019, 08:08 AM | #1 |
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E90 Alternator Field/Excite Wire?
Hi everyone,
So to cut it the chase I either get a good 14.1/14.3v at alternator and battery, or I'll get a low output of 12.3v tested with a multimeter. So, does the alternator use a field/excite wire to supply 12v at ignition to make the alternator charge? It seems strange to me that the alternator only functions one of two ways, perfectly fine or 12.1/12.3ish which can be solved by simply turning the car off and back on (rarely requires a couple of cycles) so I'm wondering if the alternator has an excited wire, there's two positive wires, one to glow plug controller, the other probably to starter motor and there's also a little wire at the bottom of the alternator, it's hard to see but I'm thinking about inspecting that first if it is that wire? |
06-20-2019, 12:51 PM | #2 |
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The alternator will have two positive connections (glow plug module & starter), it will also have a one wire plug connected to it (BSD line).
If you think the alternator is on it's way out easiest test method is to connect a multimeter to the charge posts in engine bay, run it with no consumers on and you'd expect to see around 14-14.5V. Load it up by turning all lights on, blower to max, heated rear windscreen, etc.. it should remain around 14-14.5V without too much of an issue - I was working on an E91 330D the other day, when loaded up it slowly counted back voltage wise from 14.4V to below 11V (at which point is started running rough because the voltage wasn't enough to power control units, etc.. properly). Rectified issue by replacing alternator (and consequentially battery).
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Current: 2009 E90 325i M Sport Auto
Previous: 2017 435d xDrive Gran Coupe, 2010 E90 318d SE, 2009 E90 318i SE. |
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06-20-2019, 01:13 PM | #3 | |
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06-20-2019, 01:34 PM | #4 |
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Right, measured 14.2v with nothing running. Turned heaters on full, AC on, radio on, headlights on and its providing a good 14.3/14.4 at high the alternator, battery and secret menu as showing the same. I'm going to do a journey and leave everything running and check again when I'm back but so far it's outputting enough power
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06-20-2019, 03:19 PM | #5 |
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Well, done about 40 miles and it's been perfect, AC and heaters, radio and lights on and yeah the alternator had no issues maintaining above 14v so what does that leave? Battery is brand new as well and after a drive maintains around 12.7/12.6v
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06-21-2019, 02:33 AM | #6 |
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So, if you can access the instrument cluster secret menu set it to the voltage screen.
Go for another drive and watch the voltage, when you accelerate does the voltage sporadically drop to around 12.3-12.6V? And then brake and see if it returns to 14V+, If thats whats happening id be happy to say I don't see it as an issue. 'Smart' alternators tend to switch on and off quite often when driving, for efficiency's sake BMW have tried to work it so when the engine is under load, unless necessary the alternator will briefly turn off and then turn back on when on overrun / deceleration.
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Current: 2009 E90 325i M Sport Auto
Previous: 2017 435d xDrive Gran Coupe, 2010 E90 318d SE, 2009 E90 318i SE. |
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06-21-2019, 05:00 AM | #7 | |
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06-21-2019, 05:37 AM | #8 |
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No, no issues while accelerating. To be fair having monitored my voltages constantly using the Caro0 app I would have noticed the battery dropping into red but It never does.
Oh and for crying out loud, no, I wasn't recording while driving it was my partner.. I've been called out on this before.. I don't mess with my phone while driving so please don't jump the gun anyone |
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06-21-2019, 08:40 AM | #9 |
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And this is when the car only gets 12v.. I drive around for a minute to show the voltage while it's in this state and then I restart the car twice and it randomly goes back up to 14v
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07-03-2019, 06:39 PM | #10 | |
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So, I purchased a Valeo alternator replacement brushes set (more specifically sv72) I took my alternator off and i could see that the inner slip rings where quite black, an indication that the brushes aren't making good contact, the top brush also was shorter. So I replaced the brushes and started the car and I got 12v but realised I had forgot to put the black connector into the alternator which actually connects to the voltage regulator and it rose to 14v so that in itself was interesting, if that plug isnt connected it wont output 14v, and of course if that connector connects to the voltage regulator and that is powered by brushes then if those aren't working good that would explain why it wouldn't always output 14v. Ibe started to car around 5 times now but tomorrow will be good, but man for a few hours work it cost £2.70! |
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07-04-2019, 05:08 AM | #11 |
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No scrap that after about 9 starts it went back to 12/12.3v so new battery, strong alternator that can maintain 14v new brushes on voltage regulator so what's left now I dont know unless something in the voltage regulator is actually broken
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07-11-2019, 07:47 AM | #12 |
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Going through the same process as you. Regulator ordered, new battery is in. Hating the chasing! At least my problem is constant not random. I really hate the random ones.
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07-11-2019, 10:12 AM | #13 |
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That's interesting, so yours is stuck at 12/12.3v on startup? Did you also check with a multimeter that the alternator is actually outputting 12v and not 14v?
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07-17-2019, 07:35 AM | #14 |
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My deal is new battery, not charging whilst running. Voltage regulator awaits my install, just found your callout of valeo brushes. Nice! Solder job, I get a spare regulator for cheap. Hoping it's just the regulator, lots cheaper than the alternator that's for sure. R
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07-18-2019, 05:38 AM | #15 |
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Swapped regulator, 20 minutes. Too late and too hot outside to test it out I'll be doing that tonight. Hopefully that does it otherwise it's an alternator and that's about $300. Yay for BMW. R
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07-18-2019, 12:13 PM | #16 | |
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Oh and before you buy an alternator don't forget to test or buy a ground strap first because that would stop the alternator from charging. |
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07-19-2019, 07:29 AM | #17 |
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4 aluminium e12 bolts, out she came. Cradle type mount. Simple job, liking that. Ran out of time again last night cuz I'm working 14 hours 7 Days right now. Tonight I'll run it and gather data and make sure everything is as good as I think it is. R
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01-02-2020, 01:42 PM | #20 |
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Just wondering if you've managed to track the source of your problem? I'm encountering the exact same intermittent 12v issue with my 2010 e90 as well. After a few restarts, it'll bounce back up to 13.8-14.4v. Been quoted $550 just for the valeo regulator, and $1200 for a brand new alternator. Kinda want to be sure before I start throwing parts at it.
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01-06-2020, 04:43 PM | #21 | |
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01-06-2020, 06:21 PM | #22 |
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Cheers for that. Good to hear you have yours sorted. Weird thing is once its booted up as 14+volts, it'll stay fine for the whole trip. Been checking the PTCan signals and it looks clean regardless of the state of the alternator.
Guess I'd just have to bite the bullet and replace the whole thing. Bright side is I'll have a spare alternator to tinker around with. |
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