IBS and voltage question/problem

acediac · 10-31-2015, 03:52 AM

Hey guys, I have a 2010 E90 335i.

I've got a strange electrical/voltage issue that I'm not sure is a problem and can't find anything similar in forum searches.

Recently, I had a classic battery drain problem where I go to start it and the car just goes apeshit and throws up all sorts of errors, wipers going, etc. I checked the battery and it was reading 10Volts, so that was no wonder.

I subsequently changed the battery to another 80Ah AGM identical in size and capacity, checked the battery registration(it was already correctly set to 80Ah_AGM), and reset it as a new battery using the procedures outlined here

Everything seems fine, but now when the car is running the system voltage stays at 12.3-12.7 most of the time, and occasionally runs to 14-15.5V (especially when coasting downhill). Every now and then it will ramp up to 13.8-14.2 V but will drop back down to about 12.5V after less than a minute. Sometimes at idle it will be at about 14V, sometimes 12.3-12.5V. There is also a small AC voltage but apparently that's normal.

I have monitored this via the hidden menu 9 or using INPA connected while driving or using a multimeter at the engine bay terminals when the car is stationary.

Now, if I disconnect the IBS sensor (the little blue connector), then I get 13.8-14.2 V almost constantly (+ of course the 0x2E8E IBS communication error).

Before I spend $200 replacing the IBS cable, isn't this what the IBS is supposed to do? This is a brand new fully charged battery, just been reset, so any intelligent charging system should not be pumping a constant 14V into the battery or it will overcharge it. However, everyone seems to be saying they get 14V with the engine running, even the Bentley manual. The car starts quickly, and seems to have full power. No faults or other unusual behavior since the battery change, except for this voltage thing (which I only found by accident). I assume my voltage regulator and alternator are fine, since it does sometimes get to 14-15V, and it does not overrun to 17V like some other people have reported as a problem.

My questions are:
1) Can anyone else with an IBS equipped car and a fully charged (new?) battery confirm the sort of behavior I'm seeing?
2) Is it normal/possible for the IBS to influence the system voltage like this for charging purposes?
3) Is this part of the "learning" process that the IBS does when faced with a new battery?
4) Could it be an alternator diode problem?

(Admittedly I've only gone on short < 20min trips, I will be letting the battery discharge a bit more and see if I get higher average voltages to indicate charging is taking place)

Incidentally I took out the voltage regulator to have a look at it because someone else mentioned it was a problem, but it looks fine (bushes are not black or burnt, no sign of wear). I don't know how to test it electrically though. I have included pictures here for people interested in the voltage regulator.

hassmaschine · 10-31-2015, 08:03 AM

I could be wrong - but I think that's normal.

The point of the IBS is the DME controls the alternator - it only charges the battery when necessary, because the alternator puts a load on the engine which reduces fuel economy.

Basically, the reason for the overcomplicated charging setup is for reduced emissions and higher fuel economy. it's probably a tiny difference - 1% or so - but at this stage of the ICE development even a couple % improvement is huge. Same reason newer cars have electric steering rather than hydraulic.

Wilt · 10-31-2015, 09:00 AM

The IBS monitors the current consumption of the car and monitors the battery temp. When current consumption is greater than can be supplied by the alternator, battery current is used to supply the need, and the voltage drops to battery voltage. When the current consumption is less than what can be supplied by the alternator, alternator voltage and current supplies the load and charges the battery. The battery temp determines the actual charge voltage, as a cold battery needs higher voltage in order to charge.

IOW you may simply see battery voltage at times, you might see charging voltage from the alternator at times, and the voltage which you see can vary depending upon battery temperature.

acediac · 10-31-2015, 10:59 AM

Hmm I wonder why most people report 14V with the engine running then? Even the Bentley manual says 14V is the way to make sure the alternator is working, and doesn't mention it ever dropping to 12V.

But logically, if it is meant to be an "intelligent" charger, it must be able to drop the voltage below 12.5V to stop charging the battery when necessary. I guess I will have to keep an eye on it for awhile and see if the battery stays charged up properly without being topped up.

I'd feel a lot better if someone can confirm first hand that their car behaves the same way with a full charge battery... That IBS cable is very expensive (2/3 the price of a whole battery for a measly cable!), I just want to make sure it's necessary to replace...

Wilt · 10-31-2015, 11:21 AM

Quote:

Originally Posted by acediac

Hmm I wonder why most people report 14V with the engine running then? Even the Bentley manual says 14V is the way to make sure the alternator is working, and doesn't mention it ever dropping to 12V.

But logically, if it is meant to be an "intelligent" charger, it must be able to drop the voltage below 12.5V to stop charging the battery when necessary. I guess I will have to keep an eye on it for awhile and see if the battery stays charged up properly without being topped up.

I'd feel a lot better if someone can confirm first hand that their car behaves the same way with a full charge battery... That IBS cable is very expensive (2/3 the price of a whole battery for a measly cable!), I just want to make sure it's necessary to replace...

The document that I quote is a BMW Power Management training document, and it says...

acediac · 10-31-2015, 01:04 PM

Ok, that describes a basic system, but does not address IBS. In normal cars without sophisticated electronics, the alternator would almost always be charging the battery, unless maybe when going flat out with the a/c at full blast and high powered stereo on.

In my case, I have tried turning everything off including lights, a/c, radio etc. and only cruising along with hardly any throttle, and yet it will still read around 12.5V most of the time. So it can hardly be because the car is using more power than the alternator can put out!

In BMWs, the IBS is meant to inform the DME about the condition of the battery, so that it can make intelligent decisions on how to charge the battery. And since overcharging a battery is a bad thing, I would assume you have to be able to limit the current (and in effect the voltage) to the battery at certain times, similar to how CTEK or similar battery chargers will trickle charge when the battery gets closer to full. So it doesn't make sense that we should see 14V when the engine is running at all times. The problem is I haven't heard from anyone else who have experienced the same thing...

ctuna · 10-31-2015, 08:10 PM

Most people have the lead acid battery I think.
So they will be seeing different voltages. But the
alternator output would be rpm dependent how
do they control or bypass that.

acediac · 10-31-2015, 08:32 PM

Quote:

Originally Posted by ctuna

Most people have the lead acid battery I think.
So they will be seeing different voltages. But the
alternator output would be rpm dependent you
do they control or bypass that.

Well for all cars there must be a way to constrain the voltage to a certain range like 12-15V, otherwise you would get massive overvoltages at high revs. The difference with the IBS is that it is meant to allow the system to tailor a charging pattern for the battery. I don't think lead acid vs agm has anything to do with it, in fact when you program the battery, you specify the capacity (Ah) and the type (standard or agm) so there must be different charging patterns for each combination.

ctuna · 10-31-2015, 11:28 PM

AGM charges at a lower voltage I believe
and I would guess the engineers take that into account.
But there are many cars without an exotic charging
system and AGM's are marketed to those cars as well
I think.
There is a voltage regulator someplace but how
sophisticated is it . Does it control the voltage or just
limit it.
If the profile is different between AGM and lead acid it
would make sense that the voltage is at a lower level
with the AGM.
I have used the torque bluetooth dongle to monitor voltage in both my Acura and BMW and they both pop
up to around 14 to 14. 5 with the engine running.
If you notice that aftermarket amplifiers are speced
at 12.5 and 14.5 .(motor off motor on)

10-31-2015, 03:52 AM	#1
acediac Private 30 Rep 80 Posts Drives: 1M, F30 330i Join Date: May 2014 Location: Briz, Au iTrader: (0)	IBS and voltage question/problem Hey guys, I have a 2010 E90 335i. I've got a strange electrical/voltage issue that I'm not sure is a problem and can't find anything similar in forum searches. Recently, I had a classic battery drain problem where I go to start it and the car just goes apeshit and throws up all sorts of errors, wipers going, etc. I checked the battery and it was reading 10Volts, so that was no wonder. I subsequently changed the battery to another 80Ah AGM identical in size and capacity, checked the battery registration(it was already correctly set to 80Ah_AGM), and reset it as a new battery using the procedures outlined here Everything seems fine, but now when the car is running the system voltage stays at 12.3-12.7 most of the time, and occasionally runs to 14-15.5V (especially when coasting downhill). Every now and then it will ramp up to 13.8-14.2 V but will drop back down to about 12.5V after less than a minute. Sometimes at idle it will be at about 14V, sometimes 12.3-12.5V. There is also a small AC voltage but apparently that's normal. I have monitored this via the hidden menu 9 or using INPA connected while driving or using a multimeter at the engine bay terminals when the car is stationary. Now, if I disconnect the IBS sensor (the little blue connector), then I get 13.8-14.2 V almost constantly (+ of course the 0x2E8E IBS communication error). Before I spend $200 replacing the IBS cable, isn't this what the IBS is supposed to do? This is a brand new fully charged battery, just been reset, so any intelligent charging system should not be pumping a constant 14V into the battery or it will overcharge it. However, everyone seems to be saying they get 14V with the engine running, even the Bentley manual. The car starts quickly, and seems to have full power. No faults or other unusual behavior since the battery change, except for this voltage thing (which I only found by accident). I assume my voltage regulator and alternator are fine, since it does sometimes get to 14-15V, and it does not overrun to 17V like some other people have reported as a problem. My questions are: 1) Can anyone else with an IBS equipped car and a fully charged (new?) battery confirm the sort of behavior I'm seeing? 2) Is it normal/possible for the IBS to influence the system voltage like this for charging purposes? 3) Is this part of the "learning" process that the IBS does when faced with a new battery? 4) Could it be an alternator diode problem? (Admittedly I've only gone on short < 20min trips, I will be letting the battery discharge a bit more and see if I get higher average voltages to indicate charging is taking place) Incidentally I took out the voltage regulator to have a look at it because someone else mentioned it was a problem, but it looks fine (bushes are not black or burnt, no sign of wear). I don't know how to test it electrically though. I have included pictures here for people interested in the voltage regulator. Last edited by acediac; 10-31-2015 at 04:16 AM..
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10-31-2015, 08:03 AM	#2
hassmaschine Major General 3975 Rep 7,215 Posts Drives: "NBO" 330i Join Date: Jun 2014 Location: earth iTrader: (0)	I could be wrong - but I think that's normal. The point of the IBS is the DME controls the alternator - it only charges the battery when necessary, because the alternator puts a load on the engine which reduces fuel economy. Basically, the reason for the overcomplicated charging setup is for reduced emissions and higher fuel economy. it's probably a tiny difference - 1% or so - but at this stage of the ICE development even a couple % improvement is huge. Same reason newer cars have electric steering rather than hydraulic.
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10-31-2015, 09:00 AM	#3
Wilt Major 228 Rep 1,049 Posts Drives: 2011 328i Join Date: Mar 2015 Location: SF Bay area iTrader: (0)	The IBS monitors the current consumption of the car and monitors the battery temp. When current consumption is greater than can be supplied by the alternator, battery current is used to supply the need, and the voltage drops to battery voltage. When the current consumption is less than what can be supplied by the alternator, alternator voltage and current supplies the load and charges the battery. The battery temp determines the actual charge voltage, as a cold battery needs higher voltage in order to charge. IOW you may simply see battery voltage at times, you might see charging voltage from the alternator at times, and the voltage which you see can vary depending upon battery temperature.
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10-31-2015, 10:59 AM	#4
acediac Private 30 Rep 80 Posts Drives: 1M, F30 330i Join Date: May 2014 Location: Briz, Au iTrader: (0)	Hmm I wonder why most people report 14V with the engine running then? Even the Bentley manual says 14V is the way to make sure the alternator is working, and doesn't mention it ever dropping to 12V. But logically, if it is meant to be an "intelligent" charger, it must be able to drop the voltage below 12.5V to stop charging the battery when necessary. I guess I will have to keep an eye on it for awhile and see if the battery stays charged up properly without being topped up. I'd feel a lot better if someone can confirm first hand that their car behaves the same way with a full charge battery... That IBS cable is very expensive (2/3 the price of a whole battery for a measly cable!), I just want to make sure it's necessary to replace...
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10-31-2015, 01:04 PM	#6
acediac Private 30 Rep 80 Posts Drives: 1M, F30 330i Join Date: May 2014 Location: Briz, Au iTrader: (0)	Ok, that describes a basic system, but does not address IBS. In normal cars without sophisticated electronics, the alternator would almost always be charging the battery, unless maybe when going flat out with the a/c at full blast and high powered stereo on. In my case, I have tried turning everything off including lights, a/c, radio etc. and only cruising along with hardly any throttle, and yet it will still read around 12.5V most of the time. So it can hardly be because the car is using more power than the alternator can put out! In BMWs, the IBS is meant to inform the DME about the condition of the battery, so that it can make intelligent decisions on how to charge the battery. And since overcharging a battery is a bad thing, I would assume you have to be able to limit the current (and in effect the voltage) to the battery at certain times, similar to how CTEK or similar battery chargers will trickle charge when the battery gets closer to full. So it doesn't make sense that we should see 14V when the engine is running at all times. The problem is I haven't heard from anyone else who have experienced the same thing...
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10-31-2015, 08:10 PM	#7
ctuna Lieutenant General 1921 Rep 13,122 Posts Drives: 325xi 06 wagon MT Join Date: Jan 2010 Location: Santa Cruz, Ca iTrader: (0)	Most people have the lead acid battery I think. Most people have the lead acid battery I think. So they will be seeing different voltages. But the alternator output would be rpm dependent how do they control or bypass that. Last edited by ctuna; 10-31-2015 at 11:28 PM..
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10-31-2015, 11:28 PM	#9
ctuna Lieutenant General 1921 Rep 13,122 Posts Drives: 325xi 06 wagon MT Join Date: Jan 2010 Location: Santa Cruz, Ca iTrader: (0)	AGM charges at a lower voltage I believe AGM charges at a lower voltage I believe and I would guess the engineers take that into account. But there are many cars without an exotic charging system and AGM's are marketed to those cars as well I think. There is a voltage regulator someplace but how sophisticated is it . Does it control the voltage or just limit it. If the profile is different between AGM and lead acid it would make sense that the voltage is at a lower level with the AGM. I have used the torque bluetooth dongle to monitor voltage in both my Acura and BMW and they both pop up to around 14 to 14. 5 with the engine running. If you notice that aftermarket amplifiers are speced at 12.5 and 14.5 .(motor off motor on) Last edited by ctuna; 10-31-2015 at 11:35 PM..
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