Alternator Charging issues?

TIKVA97

MEMBER
2012 CHEVROLET TRAVERSE
3.6L
6 CYL
4WD
AUTOMATIC
120,000 MILES

Voltage when car starts goes to 15v, idling for 5 minus goes down to 13.2-13.9, under load regains 14.6.

Before used to always stay between 14.6-15.4v.

I have a car audio system, 400a alternator, and 2 jy hp40 lifepo4 lithium batts. Voltage has always been somewhat of a problem to my 4000-watt amp going into protect mode before it hits lower than 13.8. I had the same amp at.25 ohm on a 250-amp alt with 2 110ah agm batteries in a 05 chevy impala, voltage stayed at 14.8 and maximum drop full power dropped to 14.2.

This vehicle has 16 grounds in total mixed with 1/0 and 4/0 cables, and duel runs of power of 1/0 from alt stud to back, and 4 power runs and grounds linking each battery using bus bars. I have triple checked all connections, made sure voltage reads the same from front to back. No resistance in the grounds.

Today my car decided to stay at 13.2v after a heavy load from my new 12k watt amp. It stayed at 13.2 until I restarted the car. It regained to 15v, but slowly fell back down to 13.2 even with driving. After some time and driving back to work, the voltage drops down to 13.9 now after settling from 15v. Before, alternator held 14.6 to 15.4v at all times and regained.

The issue also is when taking a heavy voltage drop that much, when it does regain, it regains from 13.2 to 13.7 very slow, then from 13.7 to 14.6 or setpoint in the PCM regulation jumps instantly. It's just that little drag until the alternator seems like it wakes up.

I was looking into mechman 400a alt now, the one I currently have is from gpcaraudio. Com. I am using a standard vehicle harness to plug into it. Mechman is a bit different, they turn the 2 pin into a 4 pin, and they say to put the factory harness with the box they give to trick the battery light, and 2 wires, 1 that loops back to positive stud, and another that has to be ran with 12v ignition. Will that type of alternator eliminate the PCM regulation? Because that's what I think I'm trying to do, as lithium always has to be above 13.8v. Can't have it going into sulafacion mode and causing a load on them as it's not safe.

9 Replies

KEN L

MASTER CERTIFIED MECHANIC
42,958 POSTS

"sulafacion mode"? I am not sure what you mean by this. You have the correct idea that the PCM regulates the alternator output which sounds like it is working correctly, is the problem just the monitoring charge voltage or is there something else going wrong that made you check it?

Here is information on how the system works:

The electrical power management is used to monitor and control the charging system and alert the driver of possible problems within the charging system. The electrical power management system makes the most efficient use of the generator output, improves the battery state-of-charge, extends battery life, and manages system electrical loads.

The load shed operation is a means of reducing electrical loads during a low voltage or low battery state-of-charge condition.

The idle boost operation is a means of improving generator performance during a low voltage or low battery state-of-charge condition.

Each electrical power management function, either idle boost or load shed, is activated in incremental steps. For example, idle boost 1 must be active before idle boost 2 can be active. The criteria used by the body control module (BCM) to regulate electrical power management are outlined below:

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Monday, December 18th, 2023 AT 11:10 AM

TIKVA97

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Yup, I am aware about how PCM regulates. Sulfaction mode means it goes to standby 13.2 basically limp mode for 45 minutes, as the PCM tries to restudy the data of current and battery state before returning back to normal operation, according what I've read.

The 4000-watt amp going into protect from day one was one wonder, as my lithium bank is much stronger than my agm bank I had, as well as my alternator is currently bigger, yet I never had issues with my previous system in different car non PCM regulated.

I've tried to install an RVC, told it to charge at 128hz 80% which brought voltage to steady 14.8. With it installed, yes, I could control the voltage, but during heavy bass I would see 11.5v. Without the RVC the voltage would dip to 13.6 to 13.8 with music before amp went into protect mode.

I've since changed amps, 3 days into the install, Voltage started going down to 13.0-13.2 which essentially is discharging my lithium's to only 20% capacity. Sometimes I see the battery light, sometimes I don't. But as it's going down, I try to pull over and restart the car.

The car would do this when I initially got it, I had to sand down the pillar A grounds, and front passenger pillar grounds and added more engine grounds and it made voltage always hold 14.6. Just recently it started always dipping to 13.2, within 1 minute maximum of car running its down to 13.2 and not going to unless the car is restarted.

If I go with an alternator where they switch it from a 2 pin to 4 pin that I self-wire, will that bypass this PCM system and allow alternator to always put output? I'm aware of the battery light thing, but they supply a box where you plug factory harness in to trick the light to stay off. I just need to know if it will bypass the PCM regulation, because I'm all out of ideas why everything keeps going into protect before its voltage threshold, and why my car can't keep the power held.

I even tested the lithium batteries with an AutoZone tester, it can't test lithium, but I used the deep cycle agm setting and drew 600cca from it, and they each pull 1250 cca and tester reads good. Connections solid, and my grounds should be good. Aside from maybe diodes or brushes worn, or the PCM regulation, idk why it's not charging properly as lithium discharges fastest, and technically PCM should detect it requires more voltage to keep up, but it doesn't.

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Monday, December 18th, 2023 AT 12:23 PM

KEN L

MASTER CERTIFIED MECHANIC
42,958 POSTS

"Sulfation mode" in automobiles refers to a condition that affects lead-acid batteries, typically used in vehicles. Sulfation occurs when a lead-acid battery is deprived of a full charge for extended periods. This situation leads to the accumulation of lead sulfate crystals on the battery's plates, which hinders its performance and longevity.

The problem may not be able to be fixed because the computer program detects battery condition which sounds like it is being fooled by the lithium batteries. If you change out the way the alternator works you will get a check engine light with a trouble code. I have seen people mount external alternators with the batteries for the amps being isolated. Can I ask if you noticed anything else wrong except for the bass causing the voltage to drop to 11 volts?

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Tuesday, December 19th, 2023 AT 12:23 PM

TIKVA97

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Yes, I do believe the lithium is fooling the PCM as even with low voltage it is capable of producing the amps the car needs, but voltage just stays low.

Aside from that the car acts fine even when voltage hits too low. But the battery light sometimes comes on at 13.2 when it sits there and doesn't regain, but I know its somewhat charging as it hovers between 13.3 and 13.2 just doesn't regain sometimes. Other times It can rest at 13v flat without battery light coming on.

Unfortunately, the traverse lacks room to fit 2 alternators cleanly. Also, I have just pure lithium as my bank, I never isolated anything as when components work together, in theory it should be stronger linked than isolated. Just can't mix chemistries lithium with acid or agms. Even when my lithium was discharged to 10.9v when the key was on when my sound system was being installed, the car fired right up as if voltage wasn't even low. So, it has capacity I believe.

I'll keep driving it as is, I was thinking of getting the mechman elite 370a alt for my traverse, They have a bypass for dash lights and factory plug, but they turn the 2 pin into a 4 pin and I have to wire it to ignition. Do you think the PCM will still be able to read with the factory harness disconnected or bypassed? Because that's my goal, as even though low voltage is okay, my sound system draws a lot of power. So, if it's at 13.2v and charging, when the bass hits, it will drop well in 10v range where if it charged at 15v at all times and wasn't regulated, max drop would and should be low 13s and regain instantly as batteries are heavily discharged.

Thanks for your time and your inputs, means a lot to me, especially when I don't have anywhere else to really turn! (: In the photo I'm holding 14.5 after cars been running for 15 minutes now. Compared to how it was 2 days ago, it's not dropping anymore. When it did it was from the heavy bass in idle, dropped hard, didn't regain. Restart the car, see 14.8 then starts dropping to 13.2. Now the car goes to 15.2v cold start, settles at 14.5 14.6 as it should. I do'nt know what happened, I guess the system relearned the chemistry.

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