GM van charging systems and AGM battery

[iridewheelies]

This weekend I noticed my alternator was putting out high voltage, over 15v. My house batteries are not supposed to be charged at over 15v so I am starting this thread to talk about the GM charging system and running a dual battery system. I'm also not satisfied with the way it charges while I'm driving and I think it can be improved.

What I have:

The Van - 2014 Express AWD, stock 125A alternator. No solar panels, yet.

Battery bank - 2 Sears Die Hard Platinum 31M in parallel. (These are rebranded Odyssey 31M-PC2150)

Battery separator - Sure Power 1314

The batteries are mounted inside my van, in a cabinet behind the driver's seat.



The battery separator is in the engine compartment next to the starting battery.



Batteries are grounded to the frame and the power is run with 4AWG to the battery separator through the firewall.

Here is the biggest problem. Odyssey Batteries are not supposed to be charged at over 15v according to the Odyssey tech document on the site here: http://www.odysseybattery.com/documents/US-ODY-TM-002_1214.pdf

on page 14 it says, "It is extremely important to ensure the charge voltage does not exceed 15V." But...

The GM power management will adjust the alternator to 15.5v in certain conditions. Here is the charging system description from the GM upfitter electrical guide found here - https://www.gmupfitter.com/files/media/photo/524/2014 GH Van Elec BBM SI Brief.pdf

*********************************************************************
*********************************************************************
Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode
The engine control module (ECM) controls the generator through the generator turn ON signal circuit. The ECM monitors the generator performance though the generator field duty cycle signal circuit. The signal is a pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0–100 percent. Normal duty cycle is between 5–95 percent. Between 0–5 percent and 95– 100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:

Commanded Duty Cycle Generator Output Voltage
10% 11 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 15.5 V

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is PWM signal of 128 Hz with a duty cycle of 0–
100 percent. Normal duty cycle is between 5–
99 percent. Between 0–5 percent and 100 percent are for diagnostic purposes.

*********************************************************************
*********************************************************************

The other problem I see is that when the GM charging system is at 40% or lower my Sure Power 1314 relay will open and no power goes to my house batteries. I see this as a problem because the battery bank will never be charged to 100%. The work around is to manually close the relay but I don't think that's a very good solution, I'll forget to open it back up and I don't want to leave the house battery and the starting battery connected together because they're different chemistries.

One possible solution might be to run the ground cable from the house battery bank to the engine compartment and tie into the starting battery ground. I think this might help because the GM power management is reading current and voltage with a donut (not sure what these are actually called) on the ground cable from the starting battery. The computer is making decisions based on the current going into the starting battery, it probably doesn't know the house batteries are there.

Any thoughts? How are you charging your house batteries in your GM vans?

 

[TeleSteve]

I don't have the solution for you, but I have pretty much the same scenario except I have a single 250 ah Lifeline AGM battery and a Bluesea ACR.
I have a gauge tuner and have it set to show battery voltage (as seen by the ECM). I have noticed that after start up it usually jumps up to around 14.4v occasionally 14.7v then within a few minutes it drops to 13.8v then 13.2v and after a while finally settles around 12.6v. I have suspected that when it hits 12.6v my ACR opens but haven't confirmed it yet. the Bluesea ACR can be triggered to be closed when ever the engine is running regardless of voltage which may keep it from opening at lower command duty cycles. I just need to find a circuit that is only live when the engine is running. Still need to figure out how to stop it from high voltage (14.7v+).

 

[iridewheelies]

One possible solution is using a 12v DC-DC battery charger like this CTEK http://www.amazon.com/CTEK-56-677-Automatic-Battery-Charger/dp/B005LBCVL4

I don't want to just throw money at the problem. I feel like I should be able to get the GM charging system to work for me by controlling the duty cycle.

Another thing I've thought about is swapping the starter battery to another AGM of the same type and size as my house batteries and moving the house batteries outside so they will all be at the same temperature. My thought is that the GM charging system would then treat the bank of 3 as one battery. I'd still need to limit the charge to 15v.

 

[Navi]

Im by no means an electrical person. But I've always been told that batteries should all be the same size
and similar age/condition.

 

[iridewheelies]

Navi, you are totally right. Batteries in a bank need to be the same.

In the case of a dual battery system with an isolator it's not as important because the batteries are only connected when the alternator is charging. Still, it's not ideal.

I'm going to try using a DC-DC charger. I ordered the CTEK D250S Dual. It will replace my sure power separator and as a bonus, it also has a mppt solar controller built in!

It will solve my problem of incomplete charging and my other worry of charging at over 15v.

I'm not pleased that the charge voltage is only 14.4, odyssey battery recommends 14.7. It's still much better than what I'm getting now.

It also only charges at 20A unless I add the Smartpass unit, which I will probably do later after testing the dual. The Smartpass will charge at up to 100A.

I'll report back in a few days.

 

[iridewheelies]

The CTEK D250S Dual is great!

It was really easy to install. I replaced my SurePower 1314 in the engine compartment with a 120a circuit breaker and put the D250S in the cab, near my house batteries. The terminals take 5/16" lugs and are tightened with a 5mm hex wrench.

I drove up to the ski area Saturday and back on Sunday. The D250S kept my charge voltage at 14.8 the whole two hour drive up and for the whole 2 hour drive back home, while the volt meter in my dash moved from 13 up to 15 and back a few times. In the parking lot at the ski area where my starter battery was very cold, the alternator was constantly putting out over 15 volts but the D250S kept the charge voltage on my house batteries constant. I can't say how close the house batteries were to 100% charge by looking at the open circuit voltage because my fridge cycled and heater were constantly drawing power when parked.

I am going to keep testing it for a while before I get the additional SmartPass unit.

 

[Mwilliamshs]

...I drove up to the ski area Saturday and back on Sunday. The D250S kept my charge voltage at 14.8 the whole two hour drive up and for the whole 2 hour drive back home, while the volt meter in my dash moved from 13 up to 15 and back a few times...

In other words, your house batteries (Odyssey 31M-PC2150) never fully charged. If they had, the charge voltage would've been reduced (from your observed 14.8 constant) when the battery moved from absorption charging to float. The D250S charging program can be viewed in the product manual: http://www.ctek.com/Archive/ProductManualPdf/D250S DUAL_EN.pdf. (page 21)

1) 14.8v is outside the battery's recommended voltage range. see below. It's also higher than CTEK claims possible (14.4V @ 25C)

2)The 20 amp charging current available from the D250S is insufficient for even 1 Odyssey 31M-PC2150. The battery specs straight from Odyssey state, "...a minimum of 40 amps are required with charger voltage within the range of 14.1V to 14.7V." This is, again, the spec for 1 battery, double it for your bank.

Your 200ah bank would require about 12 hours straight to recharge on the D250S from 100% discharge. Of course you'd never discharge that deeply intentionally, but Odyssey does tout their tolerance of being drawn down to 80%, which would require 10 hours of that D250S running at its peak to replinish.

3)How do you monitor the charge voltage? Just curious.

The 15v warning from Odyssey is due to the battery's safety caps opening if the battery gets too hot and spilling hydrogen, acid, etc. Bad for the battery and bad for you. That being said, I doubt your van's alternator would ever be able to damage 1 of your batteries, much less the pair in parallel, with excess voltage unless it's voltage regulation went awry. That's because the alternator just doesn't have the power to push voltage that high with sufficient current through 3 batteries and lengthy cables. If it somehow failed in such a way as to create such power, your 120a breaker would likely pop before battery vents.

 

[iridewheelies]

Thanks for your reply Mwilliamshs.

You are totally correct on most of your points. The batteries were never fully charged during the two hour drive. I am still testing out the CTEK and didn't expect the 20a current to be able to charge the bank to 100% in such a short time. I started with the bank down at maybe 60% charge. If I add the Smartpass unit the current will increase to a maximum of 100a and I expect a two hour drive will get me out of the Bulk phase and into the Absorption phase. I might also try putting my charger on the bank the night before I head out for the weekend to get me up to close to 100%. I still consider this test a success because without the CTEK my Sure Power relay opened whenever the alternator voltage dropped down below 13.2, giving me zero amps of charge. In warmer weather the relay would open a lot. In colder weather not as much, but then I have the problem of too high of voltage.

I get what you're thinking when you wrote that the alternator doesn't have the power to push the high voltage into the batteries though the longer cables, I thought that too, but I have seen it happen several times. Whenever the temperature has dropped into the low 20's or below I'm seeing voltage greater than 15 on the Odyssey battery bank. I'm currently monitoring the voltage with a plug in voltmeter I had from my vanagon days. This one - http://www.van-cafe.com/home/van/page_1207_1037/voltminder.html I haven't checked it against my Fluke meter to see if it's accurate but I have no reason to believe it would be too far out of calibration.

While idling or driving in those cold temps the voltage at my battery bank, and on the voltmeter in my dash, was up in the 15 - 15.3 range. I don't have a ammeter on the battery bank so I don't know about the current, but I didn't like the high voltage. I don't want the cells to outgas or swell. This last weekend I saw the same high voltage on the voltmeter in my dash but the CTEK kept the battery bank at only 14.8v.

I was not expecting to see the charge voltage at 14.8v, as you mentioned, the manual lists a charge voltage of 14.4v, but that is at 25c (77f) and it was much colder in my battery compartment so it's likely that the colder temp raised the charging voltage. Yes, the Odyssey manual recommends a charge voltage of 12.7, but the 12.8 is much closer than the 15+ mixed with low 13's I was seeing before so, while it might not be perfect, it's certainly much better. If you have a better idea of how to keep these batteries happy with the GM charging system please share it on this thread. I didn't start this thread to promote the CTEK, I just wanted to find the best solution.

 

[Mwilliamshs]

I think the smart pass is your shortest path to a full charge. A little solar (being mindful of the D250S' modest input capability) would be a huge step in that direction.

 

[iridewheelies]

I agree. I'm planning on putting two 100w flexible panels on the roof in the spring. That's about all I have room for, it should help a lot. The 100w panel on my syncro kept my single Die Hard Platinum topped off.

I might also replace my stock alternator with the high output stock alternator if I don't see enough charge current once I get the SmartPass.

 

[Mwilliamshs]

...I'm planning on putting two 100w flexible panels on the roof in the spring...

Be careful. The D250S has a maximum input voltage of 23v. Most solar panels designed for charging 12v systems will produce a maximum voltage of ~22v. I've not seen a maximum input current rating for the D250S but a single 100w panel should be around 5.5A so two panels in parallel (to keep voltage below 23) would be 11A.

Of course, if you're not intending to use the D250S as your solar charge controller, ignore all that^. I've never found real MPPT specs for that unit and I've looked at it pretty hard. I like the idea of the D250S but it just doesn't seem to compete with single-purpose-components, typical of a jack-of-all in my experience. Unfortunately, the D250S' (+ SmartPass) price point doesn't improve its competitiveness. I really do hope you have a lot of luck with it. I might be swayed yet.

...It also only charges at 20A unless I add the Smartpass unit, which I will probably do later after testing the dual. The Smartpass will charge at up to 100A...

I'm not sure that a Smart Pass + D250S = 100A. Could be 80A + 20A = 100A or could be 80A total. Not sure.