[aidasystemsbg]

Hello, the voltage drops from 14.6v to 12.4v when the revs change, it does when moving when changing gears, the car has manual transmissions. and when the heater fan is on and when the voltage drops and it stops for a moment and then recovers. I am attaching a video, what could be the cause, is it the regulator relay?

[huk_00]

The battery charging is controlled by the IBS sensor, try disconnecting it and check the charging voltage.

[PsevDo]

change relay at the alternator, use oem or valeo

[jaki]

change relay at the alternator, use oem or valeo

Relay in alternator? in E90? Definitely not.
I pretty sure that everything is ok, charging voltage varies a lot what I have measured.
naturalyy if it stays in battery voltage, something is wrong. probable IBS.

[evaldazj]

I have same problem, changed IBS from LCI, didn't help, change alternator, to other used one, not helped, same problem. Driving as it is now.

[Node]

First, PsevDo I believe by "relay" meant voltage regulator. Which IS on an alternator in E90, where else should it be???

Now the main question is whether the cars we are talking about are efficient dynamic editions or not!!! No one bothered to provide that info here!!!

If they are, voltage variations are to be expected when pressing accelerator AND battery charge is sufficient. Can't tell definitely, because first - video is of such extreme (as in low) quality, that it's impossible to tell when drop occurs, second - KOMBI IMHO has a small delay in displaying voltages, so it's completely impossible to tell anything from the data provided.

If cars are NOT efficient dynamics, then I would bet a voltage regulator (or it's electrodes, which are integrated) is near wearing out.

[jaki]

Good point, previous abou ED.
Still, there is no regulator as undetstood. Alternator is driven from DME/DDE, with bit serial bus, later LIN.
There is an emergency mode which remains old style charging.

[Node]

How there can be "no regulator as undetstood" when EVEN BMW part catalogue has a PART NUMBER for it!!!??? For example 12318510088, 12318510090, etc.

Where is that BSD/LIN connected then??? To coil directly??? I never replace whole alternator unless it's mechanically damaged (bad bearing, etc). 98% of time the problem are voltage regulators (including worn graphite electrodes) which are cheap to buy and to replace, most times can be done without taking alternator out at all. I pity your customers...

[huk_00]

The alternator has one BSD bus wire, if you disconnect it the alternator will output 14,2-14,5v.

[jaki]

If i remember right, both charging and cooling (A/C) drop off, when acccelerating heavily = those consume energy and that reduces accelerating power. Naturally those will be off only a short period of time.