CRD Alternator voltage

[EugeJK]

Mine is MY08 and just started on its forth D31A battery. They all lasted only ~3 years. I decided to look into the issue and share my findings here.

The alternator is modern type, internally regulated and has LIN bus for diagnostic and control from the ECU, just one wire on the 3-pin connector. My charging voltage has been randomly anywhere from 13.4 to 15.8. The ECU is meant to temperature compensate it 10mV/C. But I just monitored the opposite - the hotter it gets, the higher is the alternator output. The three of my batteries died during or after hot weather. Nothing wrong with either alternator or ECU hardware. It's Chrysler shitty software that killed my batteries. I approached two stealerships, but they had no updates for that. Neither they could tweaked the ECU via OBD2 to change charging voltage.

I worked through documentation on the alternator. It's got an electronics controller inside and for Chrysler it's factory programmed with default voltage of 14.3 that makes sense as this is mid point for D31A recommended charging voltage by alternator (13.6-15.0). If there's no LIN comms with the ECU, the alternator regulates to the default voltage.

So, the solution was to unplug the connector. I got the battery warning light on the dash, but now my charging voltage is dead steady to 14.3 and it works like old school type.

[samft]

interesting...

Mines a 2010 CRD and it sits at 13.9-14.1V the whole time

I have a dual battery set up and i think it gets up to 14.2V if i disconnect one of the batteries

Where is this connector that you unplugged? A photo would be sweet for future reference or if it starts misbehaving!

[thisisadu]

I'm on my third d31 as well. Would be interesting to look into this.
I've had similar experience with 3 year life. I have just started monitoring my voltage and will do it more carefully

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[DarrenR]

3 years is the norm for a battery.

Go back over 10 years and typically only heavy equipment such as diesel generators, elevated work platforms, cranes used to "over charge" batteries at that round 14.3V to compensate for cranking and power loss, that typically would cause constant issues with computer control modules etc etc...

Modern vehicles, for the same reason.
over voltage, engine bay heat, not getting a full charge, all leads to that life of round 3 years at best.

Some exception to this is the Land Rover Defender, the battery box is roughly sealed (as in there are 6 panels to it) and its under the passenger seat not exposed to engine bay heat, exhaust heat, or even road/ground heat, and there is airflow. Most owners do get extended life.

Regards
Daz

[EugeJK]

Originally Posted by samft

interesting...

Mines a 2010 CRD and it sits at 13.9-14.1V the whole time

I have a dual battery set up and i think it gets up to 14.2V if i disconnect one of the batteries

Where is this connector that you unplugged? A photo would be sweet for future reference or if it starts misbehaving!

Sorry, no photo was taken. It's under B+ stud terminal on alternator that's covered by the red rubber cup with sleeve. You need to unbolt the B+ to get proper access to it.

How did you measure the voltage? I was driving around for two weeks with Fluke professional multimeter set to register min & max for each trip. On average I measured 14.3-14.5

[EugeJK]

Originally Posted by DarrenR

3 years is the norm for a battery.

Go back over 10 years and typically only heavy equipment such as diesel generators, elevated work platforms, cranes used to "over charge" batteries at that round 14.3V to compensate for cranking and power loss, that typically would cause constant issues with computer control modules etc etc...

Modern vehicles, for the same reason.
over voltage, engine bay heat, not getting a full charge, all leads to that life of round 3 years at best.

Some exception to this is the Land Rover Defender, the battery box is roughly sealed (as in there are 6 panels to it) and its under the passenger seat not exposed to engine bay heat, exhaust heat, or even road/ground heat, and there is airflow. Most owners do get extended life.

Regards
Daz

The D31A has a NSN and is purchased by the US DoD. They are used in ground support equipment. The USAF report life span of 8-10 years when being properly charged. But I agree that heat inside the engine bay shortens its lifespan a lot.

[Hayesio]

My observation is exactly the same as yours EugeJK, I get 15.2 - 15.3 volt when the battery is at its hottest. I'm on my second yellow top in 4 years - 2009 JKU. My rear battery has now packed-up, its a 110ah AGM, and I've no doubt that its from the high charge voltage. I have voltage gauges on my dash for both batteries, both see 15.2V alot of the time.

I've been looking for a solution to this problem before I lash out $350 on a new deep cycle, so I might give your method a go! I was originally thinking of putting some sort of resister in the alternator +ve line to drop the voltage a little.