BMW M5 Forum and M6 Forums banner

21 - 34 of 34 Posts

·
Registered
Joined
·
992 Posts
My symptom is that it left me stranded on the side of the road with no warning at all. At about 100k. Got random errors while on the road...ABS, yellow cog, then a DSC error, then poof, shut down in the matter of a few inutes. A tow and alot of curse words later and the VR was replaced and all was well.
 

·
Registered
Joined
·
75 Posts
Discussion Starter #22
Have you guys ever had your engine temp gauge go bananas before having to replace the alternator or VR? Mine has been doing that on and off for a little while now... is the Engine temp gauge connected to the coolant temp sensor or is it a different one that is located in the engine?
 

·
Registered
Joined
·
190 Posts
If you disconnect the battery while the car is running and you crawl under the car and measure the voltage, if you see the voltage is over like 14.1V then you know the voltage regulator is bad. Note that I've never done this myself on an E60 and this can be somewhat precarious for folks doing this especially if you are not being safe on how the car is lifted up etc.

Without the battery and the alternator spinning the voltage read out anywhere on the car (given you have solid chassis ground) should be what the alternator is putting out, across the battery cables should be perfect place to measure the voltage (of course with the battery out of the circuit). If the alternator is not putting out at least ~12v then I'd expect the car to die when you disconnect the battery. The car likely expects 13.6v or something, but most systems should still at least operate below 13v. This method works on some other cars I'd looked at before, but BMW has that little integrated battery sensing dodad so maybe the car goes ape sh*t when you disconnect the battery while the car is running.

I've mentioned it in other posts too, but the ideal time to swap out the alternator is when you drop the subframe and do rod bearings. easy access to the cables and bolts, it drops straight down and you must have the pry bar. It took me longer to find the pry bar than it did to remove the alternator. It's also right around the same mileage intervals, S85 alternators often go haywire before 100k miles. The regulator and complete new OE Valeo alternator are quite cheap. IMHO based on what I've read and seen with the BMW service history on 2 of my LCI cars, the alternator has a higher likelihood of failing by 100k miles than the internal HP vanos line (LCI cars). This is why I say there is no reason NOT to do the alternator while doing rod bearings.
 

·
Moderator
Joined
·
1,743 Posts
I'd never disconnect the battery with a running engine. Not even in old carburetted cars. In a modern car with all sorts of electronics you're very likely to blow up the alternator and a bunch of ECUs in the process. More so if you suspect a faulty alternator that will have no means to keep its output in check once the battery is removed as a load.
 

·
Registered
Joined
·
190 Posts
To determine if you have a faulty alternator (or voltage regulator which is built in to it) you have to measure the voltage output vs RPM. Electrically speaking, you can't measure the voltage output of the alternator properly if the battery is connected to the car since it is wired in parallel. The measured voltage would be impacted by the battery, which is ideally at 12.6v. Alternators should put out 14.1v, the average of that is 13.4v. (note my exact voltage numbers my slightly be off, I'm basing this off what I recall that typical system design specs are, there is probably even a SAE standard on this. There is some deviation clearly based on what the battery voltage is. This is why when you code you need to maintain an ideal voltage between 13.4-13.6v.

There are machines that will test the alternator for you at certain autoparts stores. However, if you are removing the alternator in the first place for testing, I'd just replace the whole thing. Alternators should put out no more than ~14.1v (this depends on the spec from the mfg), the bench test devices have a motor and belt and simulate what the engine would do.

You could measure your current voltage in the car (alternator + battery) and if it is above 13.4v or 13.6v you'd know that the alternator is putting out more than 14.1v. However, you'd have to know what the max permissible voltage of the alternator is in the first place. I'm going to say that above 14.5v is out of spec, but that is my opinion and I'm sure there are folks that question that.

I think the E60 will automatically shut down if you tried to remove the battery based on the IBS's role in the car. I've never tried it though, and it does have some risk.

Without going too much in to the the theory of electrical engineering, I'll just stick to high level basics. It has been a long time since my circuit design classes, I'm sure others will weigh in as there likely a few EE's on here. The purpose of the voltage regulator is to regulate the output from the diode bridge. Those diodes go bad in the voltage regulator module(it contains the diodes) and that causes voltage output in excess of 14.1v. Heat tends to shorten the lifespan of diodes. The battery will never be able to provide a voltage higher than 12.6v so what happens is the effective voltage in the system is being "weighed" down if there is an overvoltage situation like 17v output at the alternator. This would be a 15v system voltage which is what your other modules are not liking and they complain. It is true that by disconnecting the battery, there is nothing to then "weigh" down your voltage and now you'd get 17v to all your modules, that all depends on what the modules are designed for as far as max voltage. I think the IBS and other logic have this as a failsafe measure, but it could be catastrophic if the alternator is putting out 18-20v (that would also mean the your system average voltage is also catastrophically high too. If the alternator is indeed putting out 14.1v or lower than 12v, and the IBS doesn't have any logic to automatically shut down the car, then disconnecting the battery would have no downstream potentially "catastrophic" impact, it will just keep running. Your alternator will not blow up, there's electrical theory or physical explanation for that.

Note that when you jump your car you are "weighing" up the voltage, because your battery is too weak.

As far as a fear of CURRENT rush destroying modules, that is fundamental misunderstanding of electrical circuits. The wires and fuses limit the current, but there would have to be LOAD that demanded such a large amount of current in the first place. Your DME or any other module is not going to "all of a sudden demand" a 40 amp load because the battery becomes disconnected, the fuse and wires would blow first if it somehow did. There are real world situations where the battery becomes disconnected unintentionally, this could be due to corrosion on the negative terminal ground wire or a one of the plates or cells fails, the battery voltage will drop significantly. Your modules or alternator should non "blow up". These situations are tested by most OEMs.

One of my M5's had it's alternator replaced by BMW based on the service records I have for the car from the prior owner. The tech said it was putting out ~17v (I say ~ because I don't have the record in front of me at the moment). The ONLY way to directly measure that is to measure the output of the alternator directly, isolated from the rest of the system (removing the battery connected in parallel). That means you have to be under the car it has to be running. You can indirectly calculate the voltage of the alternator as I mentioned above. The owner complained that he got all these random warning lights from other modules. I also happen to believe some of the other early failures that I've seen on some of these other modules like the EDC could have been related to over voltage exposure, but I have no means to prove that.

My bottom line recommendation is to replace the alternator (or voltage regulator) at or before 100k miles. I do this on all my cars (not just BMWs), because I don't like to be stranded and that is the point of preventative maintenance.
 

·
Registered
Joined
·
190 Posts
Service record from BMW dealer at 58541 miles for my 08:

"The alternator is overcharging. Checked fault memory and found overvoltage faults. Tested the output of the alternator and found when engine is under load it was putting out 17.2 volts. Drained the coolant and removed the fan. Disconnected the hoses to the radiator and removed the radiator. Removed the belts and the alternator and installed a new alternator. Reinstalled the belts and the radiator. Connected all the colland hoses and topped up coolant level. Reinstalled the electric fan. Checked battery voltage and found it to not be charged. After replacement [of the battery] road tested vehicle and vehicle has proper voltage output and runs properly."
 

·
Registered
Joined
·
2,226 Posts
So they made you pay for a rad removal/replace, coolant flush/refill, fan removal/replace (all of which doesn’t need to be done for alt swap) new alternator/remove old, and new battery plus install.....just to fix a bad battery?? Good lord that’s why I don’t go to the dealer. What that run you?? Also why I always default to a new battery when electronically issues come up and battery age is unknown or questionable
 

·
Registered
Joined
·
75 Posts
Discussion Starter #28
Kind of makes me wonder why they dont put better/bigger heatsinks or cooling systems on the voltage regulators
 

·
Moderator
Joined
·
1,743 Posts
I partially agree with GM's post. But the battery will settle at whatever voltage your alternator puts out. You can measure voltage at the battery and it will be the same as the alternator is putting out. The half a volt (if that) lost in the wiring between alternator and trunk-mounted battery is irrelevant. If you have significant voltage difference (> 1V would be my random limit) between alt and battery you either have large currents flowing in/out of the battery (no good) or you have a wiring problem. Once car is running for a minute or two current will have settled and what you measure at the battery is what you get at the alternator. More so in our cars as the IBS regulates voltage at the battery terminals, not at the alternator. Charging voltage is temperature dependent in our cars. Colder temps will result in higher V. The IBS senses battery terminal temp on top of voltage AND current in/out of the battery. So yeah above 14.5-ish at the battery on a normal day you likely have a problem.

Rectifier diodes are big semiconductors rated for hundreds of amps that need heat sinks. They are in the main body not in the regulator.

Coding voltage you only need to avoid getting a dead battery. 13.4-6 is a tight tolerance that has no merit. I've done not just coding but SMG&DME flashing on battery alone. But better safe than sorry I wouldn't recommend this to anyone.

About current rush which was mentioned, let's say your alt is putting out 100A, of which 20 or so are going to your battery when you decide to disconnect it. The alternator is a BIG inductor. How fast can you change current in an inductor? You can't. So now you have an extra 20A in the system that have to go somewhere. Doesn't matter if the regulator shuts off excitation field current at this point. Without a battery the result is a voltage spike. Ask any EE how can anyone regulate voltage output of a rectifier bridge without capacitance (which the battery provides)? Without the battery you have an unstable generator: current and voltage will be ringing. Exact scenario when you run without a battery as ign coils and injectors turn on and off, SMG pump runs, etc. A capacitor is essential to have a stable control loop. It provides instant current when a load is turned on before the alternator catches up. And viceversa. The alternator is never meant to power the car on its own.

My take on why regulators go bad is because people wait until their batteries fully die to replace them. At that point it's likely alternator or regulator damage has begun.

Just google it and one of the first link is this random but spot-on page:
 

·
Registered
Joined
·
227 Posts
My take on why regulators go bad is because people wait until their batteries fully die to replace them. At that point it's likely alternator or regulator damage has begun.
Dumb question, when will I know or what should I look for indicating that I need to replace my battery before causing damage to alternator/reg?
 

·
Registered
Joined
·
190 Posts
So they made you pay for a rad removal/replace, coolant flush/refill, fan removal/replace (all of which doesn’t need to be done for alt swap) new alternator/remove old, and new battery plus install.....just to fix a bad battery?? Good lord that’s why I don’t go to the dealer. What that run you?? Also why I always default to a new battery when electronically issues come up and battery age is unknown or questionable
This was all under extended warranty that the 2nd owner had. It was a $50 deductible, so it was almost "free". I'd say that with BMW parts prices and labor this was $1500-$2000. The reality is that you, me, and all the people that buy BMW parts and cars paid for it. The battery was killed by the over voltage output from the alternator-17.2v. When you overcharge the battery with excessive voltage or current, it will boil the electrolyte off. The capacity of the battery then becomes permanently diminished. That is what happened here.

Here is the other part of the write up on the battery diagnosis:

"58514 Battery is defective due to overcharging from the alternator. Found the battery would not hold a charge. Charged the battery overnight and the battery would not hold a charge. Ran the energy diagnosis and found nothing keeping the battery awake. Checked the battery with the Midtronics tester and found it to be defective (warranty code AM5HC-12VC9) Replaced the battery and registered a battery change in the DME."

But wait it gets better-The car was towed again to the BMW dealer on 8/1/2014.

"Customer states the car would not start not even with a jump- check and advise. Cause: 505 replace battery"

"64251 Charging battery, run short test, battery not hold to charge, replaced battery, warranty the battery 10 mon. old and drive 6000 miles, test charging system, to the midtronic all system good, registered battery, clear fault codes, test drove car, not fault code present at this time. "

The prior owner tells me that the current battery is the 5th one in his ownership time, he's had it towed 10 times and put on 80k miles over 9 years. I've said before this car eats batteries and oil. It is not a reliable car. Period. Sorry friends, that is the plain truth.
 

·
Registered
Joined
·
190 Posts
But the battery will settle at whatever voltage your alternator puts out. You can measure voltage at the battery and it will be the same as the alternator is putting out.
The battery's voltage can never exceed 12.6v, it's not physically possible for these conventional or AGM "12v" automotive lead plate battery design to do more. Yes the alternator can put out a varying voltage. The nominal voltage is designed to be 14.1v They are wired in parallel connected by very high gauge wire, so yes there is certainly resistance but it is quite low. Yes the potential (voltage) between the two points in this parallel circuit are going to be the same, which is exactly why you have to remove one of the voltage sources from the circuit to actually measure the other. No point for me to get in to Kirchoff's law. System voltage is different than the battery's voltage which is different than the alternators voltage. You can infer that the alternator's voltage is excessive because the battery's voltage can never exceed 12.6v. I'm not talking about the system voltage as it is applied across the battery to charge it.

To measure the battery's voltage, you have to measure the battery with no other voltage sources activated. This is trivial measure the voltage across the battery terminals when the car is off (no alternator spinning) but no other chargers or batteries attached (duh).

To measure the alternator's output, you can do this a few ways, but the battery cannot be in the circuit, as it's voltage will affect the measurement. You can disconnect the B+ terminal but the car has to be running to spin the alternator. I would NOT remove the B+ while the car is running. The car can run off the battery alone, but not for long. This is what the BMW tech did. If the system's voltage was measured to be 17.2, that would imply an alternator output voltage of over 20v. The other measurement method is what I mentioned earlier, because it's wired in parallel.

The IBS is a sensor not a voltage regulator for the battery. Furthermore there are 6 diodes, a set of 3 that are heat sinked and convert the AC to DC, then a 2nd set of 3 that regulates the field current which controls the total power output (voltage and current). This is how you get a constant voltage despite changes in alternator speed. These are the diodes that can fail.

Heat kills alternators, the heat has no effect on the flux of the magnetic field-the magnets and windings are ok with the heat. It's the diodes that overheat and make the voltage regulator bad. We're lucky to not have the disastrous water cooled alternators that some earlier BMW's had. They were watercooled to dissipate the heat from the diodes, because those cars had very high amp output requirements.

I'd avoid coding anything with less than 13.4v let alone 12.6v, clean stable voltage is critical when reprogramming flash memory, but you seem to have your own opinions on the merits of that and what BMW states in their procedures. A fully charged factory battery is 92aH, and yes that is plenty of capacity for certain quick programming tasks.

The actual charging current for the battery is less than 10A. It never sees anything near 100A. You will kill a battery trying to charge it at 100A. Once the car is started that ALTERNATOR is what is powering the electrical needs of the entire car. The battery does offer some properties vaguely similar to a capacitor, but has no where near the ability to deliver the power in such a short amount of time as a cap. The alternator is fully capable of running all the power needs of the car, that is it's job in life. With auto start and stop a high duty cycle battery is needed (because the engine stopped and the alternator is delivering zero power. I did not say the alternator is meant to power the car on its own, but it can. I agree that battery does serve other purposes in leveling out the voltage.

I can't possibly disagree with you more on your statement that it is the battery that kills the alternator or the regulator. I also gave the real world example of a M5 that I now own that had a failed alternator (voltage regulator) which killed the battery. However, perhaps you are correct in your own theories. I'm not going to bother with googling other random stuff, there is a ton of stuff on the internet to support anything.
 
21 - 34 of 34 Posts
Top