[giorgi]

hi guys, today i measure voltage on the battery and it seems overcharging when car idling it shows 15.5v almost 17v,is it bad voltage regulator or must change whole alternator

[sredwine]

Did you recently change your battery? You must register the new one in your car's computer-it adjusts charging as the battery ages and this would cause it to overcharge a new battery. You can use software like BMW Logger to register a battery.

[Pladi]

It will probably do that due to a bad battery. Or a battery that has not been registered correctly..

[mxchris727]

Both responses above are incorrect. Change out the voltage regulator on the alternator and that will solve your issue.

https://www.ecstuning.com/b-bosch-pa...317561939~bos/

[gT-BMW]

i agree. no matter how dead a battery is the alternator should never charge more than 14.4 volts. at that voltage your alternator should be charging at its max amp.

[330istocknot]

Fixed your Voltage alternator before it fries something, or just get a new alternator. I had mine overcharge at 17V and friends a bunch of things, had to sale the car as parts after that... Dont wait for it to happen...

[Blackhawk36]

17 volts will cook your battery. I bet it is very warm to the touch after running for a while.

[giorgi]

today i measure with multimeter and when idling voltage gous 15.9v, and dashboard came like a christmas tree here video link

[giorgi]

what is normal voltage when idling?

[sredwine]

13.6-14.4V depending on charge state and age of battery.

[sredwine]

What is your battery voltage with engine off? Normal is 12.6-13.2 depending on charge state. If it's good battery with that much charging voltage it should be at the high end of that range. Sounds like a bad regulator-don't fry your car-fix it.

[giorgi]

when car is off voltage is 13.61, i think it overcharged cause regulators bad function

[giorgi]

but curious thing is that it happens only hot weather:@

[330istocknot]

Change your alternator, don't fry your car plz.

[giorgi]

so, i saw that my voltmeter lying 2volt higher and my battery just goes bad so there is not problem with alternator or VR so i change battery but after 5min it begun again

[cooldude346]

Hi, I think the problem is most definitely your alternator. This happened to me last week. I was driving along an interstate and all of a sudden my dash lights up like a Christmas tree (transmission malfunction, abs malfunction, brake malfunction, flat tire monitor malfunction, traction control malfunction along with many others). I drive for another 10 seconds and my windshield wipers stop working too and its pouring while im driving about 50 mph and can't see anything. Then I manage to pull over and as im doing so I get a "control systems failure" notification. I decide to restart my car because thats what i do when I get my daily half engine power light and it resets. However then the car wouldn't turn over.
I called triple A and the truck came 30 mins later. The truck driver tried to start it and it started fine. Just as I was about to drive off the lights all came back so thankfully I got it towed to my mechanic.

He said over voltage was the issue. Replaced the alternator for $1000 and its all fixed now ($600 for the part and $400 for labor).

Apparently if you keep playing with it and trying to diagnose further you can fry the battery.
If you got all those Christmas light and signs of over voltage change your alternator ASAP.

As far as I know our BMW's have the voltage regulator built inside the alternator. The easiest thing to do is just to change the whole thing.

Lastly, if you did end up changing the battery its imperative that you get it programmed/registered to your car through a dealer. Otherwise you may still have some sort of voltage issues.

[banglenot]

My 530 uses a Valeo; my 328xit uses a Bosch. Both are N52's.

I've replaced both regulators as PM's. Each costs less that $40.

The valeo had 3/4 brush wear at 100K; the Bosch was 1/2.

The replacement is easy, and is almost identical on the two brands.

Remove the serpentine. Remove the 4 aluminum bolts, the battery link and the bus plug. Take the alternator to the bench.

Three screws to remove the cover; 3 (or 4) screws to remove the regulator. Put the new one on and reassemble, with new aluminum alternator bolts. About 45 min to do the entire job.

On most alternators, the only wear point is the regulator/brushes. Though a bearing or a diode can certainly fail, it's rare. I suspect most alternator swaps should be regulator replacements.

So, save $550 and DIY it with regulators.

[e90yyc]

+1 on replacing voltage regulator. Cheap and fairly straightforward.

I'm going to disagree with the posters here who are saying that ~14.5 volts is the highest you should ever see. Assuming your car has IBS, the DME will compensate for ambient temperature.

Now that weather where I am is warm, I see roughly 13.5-14 volts.

In the middle of winter, when temps were below 0 degrees F, I saw as high as 15.5 volts, with averages around the 15 mark. This was normal. No issues with voltage regulator or charging circuit.

None of the above changes the fact that you clearly have a problem with your voltage regulator; I just wanted to put this on the record as I had a hell of a time finding this info myself when initially trying to determine whether the voltages I was seeing were normal. My battery was quite new and had been registered correctly.

Good luck!

[=C=]

As others have said, replace the voltage regulator.

The alternation is fine as it's charging. The voltage regulator sends the appropriate voltage and amps to the battery depending on load and max is 14.4~

I just changed mine as it wasn't charging the battery at all. My initial assumption was alternator but it was actually the voltage regulator.

[mattoak]

Adding my recent experience as its similar, however I didn't measure the voltage.

For the past week or two randomly when first starting my car I'd get a warning ding and a red battery symbol on the dash. Car is 2006 325i with 165k miles. Owned it since 2011 and 70k, never changed alternator or battery so I figured it was one of the two, but naively thought I could wait until the battery died, jump start it, and then get home and figure out if it was battery or alternator. Started getting the red battery warnings a bit more over the past day or two, then this morning a few miles from home I got it a bunch of times in a row, instrument panel lit up like crazy, speedo started freaking out, and slowly things started shutting down like the radio and blinkers. Soon after I pulled over and the car basically just shut off and wouldn't turn back on.

Got it towed home and pulled the old alternator and took out the voltage regulator. The brushes are basically worn down to the level of the center shaft. Putting it back on they barely touch.

I figure its the voltage regulator and ordered a new one for ~$50. I'm also going to fully charge the battery for good measure and keep an eye on its charge level but I don't think it was the battery since I just broke down like that and then had a dead battery to go along with it. We jumped the car to drive it onto the flat bed and it would only run with the jump box attached to the terminals under the hood. As soon as you take it off the car dies again. I'll probably get a new battery soon anyway as its old and on really cold winter mornings sometimes can struggle a bit.

[Ronin416]

Might as well jump in and share my experience and a suggestion as well.

For months not weeks, my car would sometimes show the battery light and randomly the halo’s wouldn’t come on. Obviously the computer was conserving battery.

Then a couple of days ago, with 100k on the car. It goes beserk!
Like earlier posters said, tranny wouldn’t shift, tried resetting, wipes going crazy wouldn’t turn off. Waterpump stopped working, overheat warning. But I knew that wasn’t true as it just happened and that probably comes on when the waterpump stops, just to save engine or your wallet.

I’m replacing the alternator entirely. There may be more brush life left but since it’s out I might as well be safe than have a wear out issue cause I just replaced the voltage regulator. Plus the N54 is not as friendly to get to (I’m guessing) as the N52.

Oh and I bought a new battery thinking that would solve the issue, but no. At least I had a reason to get rid of the factory battery as who know how long it’s been in there.

A word of advice from a BMW tech, replace your “ground cable or strap) it’s the one on the driver side (North America) close to the motor mount to the chassis. Braided silver wire, don’t wrap it. Yours is probably black and some may be even brittle. When this goes, it can cause similar problems. This is roughly a $45 part.
If you live where there’s snow or have high mileage replace it. You wouldn’t think a simple ground wire cause such issues. Plus if other shit goes wrong you know you covered that base.

Fingers crossed this car works fine when I get it back tomorrow.

[nsjames]

Originally Posted by Ronin416

A word of advice from a BMW tech, replace your “ground cable or strap) it’s the one on the driver side (North America) close to the motor mount to the chassis. Braided silver wire, don’t wrap it. Yours is probably black and some may be even brittle. When this goes, it can cause similar problems. This is roughly a $45 part.
If you live where there’s snow or have high mileage replace it. You wouldn’t think a simple ground wire cause such issues. Plus if other shit goes wrong you know you covered that base.

this is true, also the oe on the passenger side. being right next to the washer bottle fill and getting methonal spilled on it all the time isn't good for it either. Mine had all of the plating gone and was half way rotten through where the braid was crimped onto the lug.

I replaced it with a 9" long standard braided ground strap. It was $6 on ebay. I had to bend it's lug a touch to clear the heatshield. It's larger and far cheaper than the BMW part.
https://www.ebay.com/itm/9-long-Univ...0AAOSwFc5XwHku

a new voltage regulator and ground strap made all my electrical voltage strangeness go away.