Disconnecting the battery to diagnose high drain
03-19-2014, 05:41 PM
#21
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Because the production of current from the alternator requires mechanical work, and the greater the current output the greater the corresponding drag put on the serpentine belt turned by the engine, during starting of the car the alternator is completely disconnected so that it doesn't create drag on the engine while the starter motor is turning the engine (and the serpentine belt and alternator connected to it). Once the engine starts and the alternator belt spins the alternator up to a certain speed, a field current is then applied internally and the alternator begins to convert mechanical work to electricity, ramping up its current output slowly over about 10 seconds, climbing to achieve a system voltage of around 14.2V.
The cars entire electrical system includes all of the power consumers (computers, radio, heaters, lights, etc.) as well as the battery, which are all seen by the alternator as a single load. Once the alternator stabilizes its output, the voltage regulator on the alternator works with the CAS and ECU to maintain a defined system voltage level (generally around 14.2V which is the normally the best voltage to place across the battery terminals to properly charge a battery). When you turn on an additional load consumer, the system voltage will go down and the alternator responds by adding more field current to the alternator which increases the current output and brings the system voltage back up to where it was. When loads are turned off the system voltage will go up, and then the alternator cuts its current output to drop the system voltage back to the designed level. The system is constantly adjusting itself multiple times per second.
Based upon the battery state of charge, ambient temperature, battery negative terminal temperature and recorded history of the battery state of health, the ECU may decide to vary the system voltage up or down (generally in a range of 13.8V to 15.5V, depending upon the type of battery registered in the system), to either accelerate or decelerate battery charging. Again, this is done by varying the alternator current output. BMW 5-series alternators generally are 150 amp or 180 amp units, but by design only put out a fraction of that output to improve reliability and extend the life of the alternator.
If the alternator is operating properly its output is never completely stopped, or even lowered to allow the system voltage to drop below 13V as the battery could then be discharged.
03-21-2014, 10:28 AM
#22
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My Ride: Jet Black 530i with some mods
Thanks for the valuable info BimmerFan52. I disconnected the IBS and my battery hasn't drained. It seems to be the culprit. I'll test it for a couple more days before order a new negative terminal with IBS just to be sure. I love this forum! 
You are somewhat correct. System voltage (which is also seen across the battery terminals and affects the rate of charging) is varied by changing the alternator current output, but the alternator is designed to never completely stop producing current while the engine is running (in a non-hybrid automobile).
Because the production of current from the alternator requires mechanical work, and the greater the current output the greater the corresponding drag put on the serpentine belt turned by the engine, during starting of the car the alternator is completely disconnected so that it doesn't create drag on the engine while the starter motor is turning the engine (and the serpentine belt and alternator connected to it). Once the engine starts and the alternator belt spins the alternator up to a certain speed, a field current is then applied internally and the alternator begins to convert mechanical work to electricity, ramping up its current output slowly over about 10 seconds, climbing to achieve a system voltage of around 14.2V.
The cars entire electrical system includes all of the power consumers (computers, radio, heaters, lights, etc.) as well as the battery, which are all seen by the alternator as a single load. Once the alternator stabilizes its output, the voltage regulator on the alternator works with the CAS and ECU to maintain a defined system voltage level (generally around 14.2V which is the normally the best voltage to place across the battery terminals to properly charge a battery). When you turn on an additional load consumer, the system voltage will go down and the alternator responds by adding more field current to the alternator which increases the current output and brings the system voltage back up to where it was. When loads are turned off the system voltage will go up, and then the alternator cuts its current output to drop the system voltage back to the designed level. The system is constantly adjusting itself multiple times per second.
Based upon the battery state of charge, ambient temperature, battery negative terminal temperature and recorded history of the battery state of health, the ECU may decide to vary the system voltage up or down (generally in a range of 13.8V to 15.5V, depending upon the type of battery registered in the system), to either accelerate or decelerate battery charging. Again, this is done by varying the alternator current output. BMW 5-series alternators generally are 150 amp or 180 amp units, but by design only put out a fraction of that output to improve reliability and extend the life of the alternator.
If the alternator is operating properly its output is never completely stopped, or even lowered to allow the system voltage to drop below 13V as the battery could then be discharged.
Because the production of current from the alternator requires mechanical work, and the greater the current output the greater the corresponding drag put on the serpentine belt turned by the engine, during starting of the car the alternator is completely disconnected so that it doesn't create drag on the engine while the starter motor is turning the engine (and the serpentine belt and alternator connected to it). Once the engine starts and the alternator belt spins the alternator up to a certain speed, a field current is then applied internally and the alternator begins to convert mechanical work to electricity, ramping up its current output slowly over about 10 seconds, climbing to achieve a system voltage of around 14.2V.
The cars entire electrical system includes all of the power consumers (computers, radio, heaters, lights, etc.) as well as the battery, which are all seen by the alternator as a single load. Once the alternator stabilizes its output, the voltage regulator on the alternator works with the CAS and ECU to maintain a defined system voltage level (generally around 14.2V which is the normally the best voltage to place across the battery terminals to properly charge a battery). When you turn on an additional load consumer, the system voltage will go down and the alternator responds by adding more field current to the alternator which increases the current output and brings the system voltage back up to where it was. When loads are turned off the system voltage will go up, and then the alternator cuts its current output to drop the system voltage back to the designed level. The system is constantly adjusting itself multiple times per second.
Based upon the battery state of charge, ambient temperature, battery negative terminal temperature and recorded history of the battery state of health, the ECU may decide to vary the system voltage up or down (generally in a range of 13.8V to 15.5V, depending upon the type of battery registered in the system), to either accelerate or decelerate battery charging. Again, this is done by varying the alternator current output. BMW 5-series alternators generally are 150 amp or 180 amp units, but by design only put out a fraction of that output to improve reliability and extend the life of the alternator.
If the alternator is operating properly its output is never completely stopped, or even lowered to allow the system voltage to drop below 13V as the battery could then be discharged.
06-03-2021, 08:34 PM
#23
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My Ride: 2008 E60 525 xi
Congratulations on your car. Your question is a good question (we don't take off points for newbie questions).
Usually the only thing you will have to reset is the clock, and maybe some radio station presets or seat memory presets.
When measuring for parasitic current, the closed circuit current spec is around 40mA.
One thing you might first try is to disconnect the IBS (Intelligent Battery Sensor) which is part of the negative battery cable, and is a problem with early E60s. It is a small microprocessor that constantly measures battery voltage, current coming into the battery and leaving the battery, and the acid temperature of the battery in order to help the ECM (main car computer) understand the battery's general state of charge. Depending upon the battery state of charge the ECM can tell the alternator to increase or decrease current to the electrical system, with the effect of raising or lowering the system voltage to accelerate battery charging.
One of the tasks of the IBS is to wake up the ECM (which normally goes to sleep once the car has been turned off to conserve battery power). If the car were turned off, but the key was left in the on position with the radio, seat heater, etc. left running, then after a period of time the IBS senses the battery is being drained quickly, and can wake up the ECM which will turn off a relay to interrupt power to these "non-critical devices". After this event the ECM is designed to go back to sleep.
A properly operating IBS will only wake the ECM once. But early versions of the IBS were improperly designed and allow moisture to damage the unit, sometimes causing it to malfunction and repeatedly wake up the ECM and drain the battery.
From the negative battery cable you will see a small wire with a blue plastic terminal on the end. Disconnecting this wire (the communication line between the IBS and ECM) will prevent the IBS from waking the ECM. It will not hurt the battery or prevent it from being charged.
After disconnecting the IBS make sure the battery is fully charged and then wait. If the battery stays charged then your IBS is the source of parasitic discharge. If not then good luck on your continued hunt!
Cheers Mate!
Usually the only thing you will have to reset is the clock, and maybe some radio station presets or seat memory presets.
When measuring for parasitic current, the closed circuit current spec is around 40mA.
One thing you might first try is to disconnect the IBS (Intelligent Battery Sensor) which is part of the negative battery cable, and is a problem with early E60s. It is a small microprocessor that constantly measures battery voltage, current coming into the battery and leaving the battery, and the acid temperature of the battery in order to help the ECM (main car computer) understand the battery's general state of charge. Depending upon the battery state of charge the ECM can tell the alternator to increase or decrease current to the electrical system, with the effect of raising or lowering the system voltage to accelerate battery charging.
One of the tasks of the IBS is to wake up the ECM (which normally goes to sleep once the car has been turned off to conserve battery power). If the car were turned off, but the key was left in the on position with the radio, seat heater, etc. left running, then after a period of time the IBS senses the battery is being drained quickly, and can wake up the ECM which will turn off a relay to interrupt power to these "non-critical devices". After this event the ECM is designed to go back to sleep.
A properly operating IBS will only wake the ECM once. But early versions of the IBS were improperly designed and allow moisture to damage the unit, sometimes causing it to malfunction and repeatedly wake up the ECM and drain the battery.
From the negative battery cable you will see a small wire with a blue plastic terminal on the end. Disconnecting this wire (the communication line between the IBS and ECM) will prevent the IBS from waking the ECM. It will not hurt the battery or prevent it from being charged.
After disconnecting the IBS make sure the battery is fully charged and then wait. If the battery stays charged then your IBS is the source of parasitic discharge. If not then good luck on your continued hunt!
Cheers Mate!
I was looking for an anser on Google and it sent me to this link. I have a related question about charging my battery. I typed this once and it auto saved but I cannot find where that auto save is to bring it back. Oh well, after rebooting for a dead laptop battery I guess I will just have to type it again. Sorry if this upload twice.
I have a 2008 535 ix that I just bought from Copart. It has driver's door damage and I have a donor car. The air bag had been deployed.
I put in the key fob. No lights came on but the dash lights flickered on an off for a couple of seconds when I pushed the start button. I also pushed the key in against a springy detent, put my foot on the brake pedal and pushed the gear selector lever a little stiffer into the park slot. I'm not sure if any of this helped to get those lights on but I could not reproduce it twice. The lights acted like the battery was low because the starter solenoid did go click click click for a few times. The next time I tried it nothing came on except a no key symbol right in the center of the instrument cluster.
I boosted the battery and nothing happened. Not even the no key symbol.
I put my 2 amp trickle charger. I wasn't getting much so I hooked another battery in parallel. I did this because sometimes this Sears charger won't charge an ACM battery without hooking another battery in parallel. With the charger on, the 4 way (location) LED's strobe really fast. The charger needle moves a small amount in time with the strobing. I think this might be the voltage check function of the BMW? You wrote that it was ok to charge the battery with the battery terminal leads in place? On the fuse box in the trunk, there is a black relay all the way up in the top left. This tick tick ticks and seems to be the thing that is causing the flashing of the LED's and the battery trickle charger meter needle - in unison. I removed the negative battery terminal lead and I am charging things overnight. I was afraid to keep that relay ticking for 8 hours. I'm not sure how long cars sit at Copart, perhaps a year. The battery is a BMW and looks new. I'm sure it cannot be a 2008 battery so the previous owner must have opted to continue with BMW branded batteries. I sure would like to get this to turn over and start. After the battery is charged tonight, do you have any sequence of events for when I do try to start it?
I have and e39 that I have been driving for years, after buying it with a bad engine due to the timing chain guides problem. I took it somewhere and had it rebuilt for $9,000 USD. Yup, that was the final bill. That included new rod and crank bearings but not turning the crank or resizing any caps. The machine shop said that all of the clearances spec'd out well. Stock rings went in and the heads were rebuilt. The put all new valves in from BMW. Why they did not go to Kimble-White like I had asked, who knows. Doctor Vanos rebuilt both. It was a crazy price but I kinda' got trapped. They went out of business due to a lack of business. Anyway, I have a great car. One of the reasons why I am telling you all of this is because I don't have any experience with the e60 key system so I don't yet know how to trouble shoot this problem. I am very anxious to see if all the six cylinders can awaken from their Copart slumber.
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