Battery over Charge

[ghosty]

Hi All,
I have just picked up my new truck complete with, brand new LMM 2010 and Edge CTS unit. COmplete my first journey the yesterday with a major issue.

I have an alternator that is over charging my batteries and causing them to vent massively and die.
I have just completed a 4000km + journey and have fried the original battery and the new battery I bought part way. Along with this other items in the car are starting to go from excessive voltage.

The alternator is a Bosch BR14-C-R 125amp (has two battery connections Bat1, Bat2) it is putting out 15Vdc, with every thing electrical turned on in the car it is putting out 14.8Vdc, still to much.

Can anyone tell me how to reduce the charge rate down to 14v please. I have read it can be done in the ECU, I have an edge CTS, not sure if I can use this to adjust ECU. I am a noob to the CTS and the 6.6 Dmax

Thanks in advance.

 

[chevyburnout1]

That voltage sounds slightly ok to me personally. Yeah it's a little on the high side but I wouldn't see that taking out batteries or electronics. The ECM does not control the charging system on your truck. It's all internal to the alternator itself. Are you saying the alternator has two big power studs to hook up the main charge-back wire? If so that does not sound factory. Take the alternator in and get tested, or replace it with a good GM/ACdelco unit.

Usual voltage I have seen on LMM's have been 14.2-14.8v. On start-up I'll see 15.1-15.2.

 

[ghosty]

Thanks for the reply, the alternator is brand new, on my vehicle the alternator field is set by the ECM, not self regulated. I think its core 38 (maybe 32) on the ECM harness.

At least this is what I believe to be the case, the electrical drawings I have support this as well.

So I suspect there is a code in the ECU that can be adjusted up or down to drop the voltage. The maintenance free batteries I have are good for 14.1 for boost charging but not 14 hours of driving, being charged at 14.8 to 15vdc rate.

Can anyone tell me what code to look at in the ECU and the if this can be done with third party tools or do I need a genuine GM unit to make the adjustment.

 

[onebaddmaxxx]

Gm tools (tech 2 or MDI) and EFI Live DO NOT support altering a code for the charging system.

I would just ditch the junk aftermarket alternator, go back to factory stuff and be done with it. :thumb:

 

[THEFERMANATOR]

The ECM does not control charge voltage, it simply turns the field on and off to the alternator and senses the no charge circuit. The alternator's regulator controls the charging system voltage. I know mine will reach close to 16 volts on a cold start, but tends to level off around 14-14.5 volts when hot.

 

[ghosty]

thanks terminator for clearing that up about the ecm / field on off.

will have to have a look at the regulator.

 

[N2BRK]

my LMM with a stock charging system charges high like that too. I was really worried but my mechanic buddy told me it's the new norm. I'm still concerned since I'm programmed to think dash bulbs start popping a little north of 15vdc, lol... so I'm behind the times I guess.

 

[ghosty]

I can understand an alternator charging at a high rate for a short duration due to load etc. But it is not sustainable if you want your batteries to last.

At 14.4 Volts batteries start gassing, there are some exceptions to the rule such as Optima. But most lead acid starting batteries start gassing off. This is not good.

Mine was gassing off at 15Vdc continuously, but the heat of the engine bay and the 40 Degree Celsius day killed the battery. In colder climates or with different batteries the 15vDC may be suitable. But not down under with our high temps

I need to get the car into the workshop and get the alternator off and adjust the regulator by "tweaking" the regulator

 

[ghosty]

HI All,
Back on this problem again, I bought a 13.8vdc reg from a place in the States. replaced the reg i the Alternator.
Same thing 15Vdc output yet again.
Spoke to the Alternator guy in the states and he says that reg / alternator voltage is determined by the PCM (assume he means ECM in DMAX)
Looked up the drawings, and the e;ectrical drawing shows a pull down switch (variable) and a bridging switch on the same output to the field. SO this aligns with what the alternator guy says.
Does any one know where to set this voltage using a Tech 2? I can see the voltage as an Info filed but don't know where to adjust it. I have only had my Tech 2 for a day, so I am unsure where I should be looking.

Thanks in advance

Ghost

 

[ghosty]

Hi,
Thinking about it, I don't have a battery temp sensors will this be an issue? not sure if its meant to have one or not but I dont.

Also whats the chances there are two versions of ECU or flash one for cold climates ie 15vdc is suitable and one for hot climates where 13.8 is all you want to be doing.

Thanks
Ghost

 

[onebaddmaxxx]

As I said before.....you can not change alternator settings with a tech2

 

[ghosty]

OK,
can it be changed with an MDI and the software, if so what area should I be looking for?

 

[onebaddmaxxx]

No an MDI is just a newer version of the tech 2 because it does not require you to pull the vehicle info from the vehicle first. Saves time by wirelessly connecting to vehicle to flash it. Its required for 2012+ newer gm cars, and 2014+ gm trucks

 

[THEFERMANATOR]

The ECM in a DURAMAX does NOT control the charge in any way except it provides the switched input to the alternator to field it. This is done because gassers DO control the charging voltage, so it only made sense to use the ECM to trigger the alternator.

 

[ghosty]

Ok, that's the second time you have told me the ECM doesn't change the field voltage to the regulator. Thanks for reminding me of that I was getting lost in the Suppliers info and not thinking logically about it.

The Supplier of the Bosch regulator I bought, (which is the same model alternator as the truck comes out of the factory(its genuine not aftermarket)), says the field strength is set by the PCM, and you have now added the info about the Petrol trucks vs Diesel trucks. so this all makes sense.
The ECM is controlling the charge rate on the diesel, however it is a fixed value. The drawing show a pull down resistance value, so based on what you have said this is the cause of the over voltage.
Either the model of ECM I have has a higher "Charge setting"(read: fixed resistance value) or the ECM has a fault in it.
As ultimately its the ECM that controls the field strength in the reg on the alternator. As you say the petrol units alter the voltage, and a diesel is fixed. The alternator is the same unit and is set up to be variable.

So If I put a resistor in the field line out to the alternator, this should lower the value of the Field output voltage, thus the Alternator Voltage.

Any one have any idea's what wattage resistor I would need, and I will calculate a starting point for the ohms.