Adjust Battery Charging Voltage With ECU

[MrAl]

Hello all,

I have been reading, or should i say rereading, about wet lead acid batteries and AGM lead acid batteries. What i found in some detail is that the charging system of a car is not the ideal way to charge a battery of either type beacuse the cahrge regimen is not right. I've dealt with various types of batteries that have to be charged and i have seen somewhat large differences in the way different batteries should be charged, ideally. This includes Lead Acid, NiCd, NiMH, and Li-ion.
OF those i have deal with Li-ion the most but also with NiCd and NiMH having designed chargers for all three types.
To quickly run through the differences in charging these three, NiMH is best charged with a negative delta V regimen, while NiCd can take that also but also a simple DC wall wart and series resistor for a somewhat tapered current regimen. Li-ion was my favorite, because the charge regimen is very well defined and not too hard to accomplish with various types of circuits. The regimen goes like this... First the cell is charged with a regulated current, and when the voltage reaches some high level the current starts to decrease and it switches to voltage regulation which only allows the cell to get to 4.20 volts max. Lead acid requires a multiple stage charging process to charge in the best possible way.
The main point here though si that different battery chemistries require different charge methods and if hte method is not right the battery life suffers.

Now back to the car and the alternator charing schemes. Some cars were made for wet lead acid batteries not AGM batteries. According to what i have read recently and before, AGM batteries require about 0.2 volts more voltage to charge the battery correcty, as well as the proper multistage regimen.
Since the car can not do the regimen correctly, we fall back onto the voltage alone. The short story is that AGM really needs that extra 0.2 volts all other things equal as compared to wet lead acid.

Now to my car. Mine is the 1998 Volvo v70 non turbo. The battery charges at 14.0 volts constant and never changes unless maybe there is a load on the battery like the heater or something, but something is keeping that voltage at 14.0 volts and i think it is the ECU (the computer). The older cars had a built in regualtor that was built into the alternator.

So the question is, since most batteries are AGM today can we program the ECU to allow the battery voltage to charge at 14.2 volts intead of 14.0 volts? I believe that would solve all of my battery problems.

I had the same problem with the old Hyundai i had. The battery would go lower and lower until i would have to bring it into the house and charge it with a home battery charger. After that, i could go a month or two until i had to repeat that. This was with a new battery too. The only way i knew to modify that was to dig into the alternator and install a series Schottky diode to make the regulator think the battery voltage was about 0.5 volts too low and so charge it with a higher charge rate.

But anyway, is the ECU programmable for the battery voltage in this car and if so how hard woutd it be to program a different voltage for the chargeing process?

A side questoin is, i wonder if the newer cars have a better way of charging the battery than the older cars. That is, some sort of multi stage regimen instead of just a constant voltage.

Thanks a bunch.

[abscate]

I don’t think the ECU has any role in battery charge. I think you have to define what your battery problem is. If it is low use leading to discharge of the AGM would say the solution is spend less money and buy a conventional flooded cell.

I use trickle , 1-2 amp chargers on all my cars that aren’t daily’s, especially in winter. Batteries are 5 year replacement items, I stretch the life by using the weak ones in my cars and carry a jump pack. SWMBO gets the new one, I cycle her good battery down the pecking order, I’m at the bottom

When they finally get to the point where I have to jump after one day, Neil buys them as spares

[duke1]

hi the alternator is internally regulated on most cars and ecu has no function re charging as far as i know i only use ordinary lead acid battery so cant comment further,good luck

[Chuck W]

The alternator is internally regulated.

You should expound on what your "battery problems" are.

[454cid]

I disagree that most new batteries are AGM. AGM is still high-performance/upgrade/fancy.

I'd contact one of the small alternator rebuild shops that are online, and ask if your alternator is internally regulated or controlled by the PCM. You may be able to tell that yourself, given the parts list they they have for a rebuild. What are Volvo alternators.... Bosch? You might be able to find a rebuild video on Youtube, where the re-builder talks his way through it and mentions regulation.

Given the date, I'd guess internally regulated, but I don't know Volvo.

[Chuck W]

A '98 does not have a PCM. It uses the Motronic M4.4 ECU, not the ME7 of 99-00's and the P2's.

It has an internally regulated alternator.

[454cid]

A '98 does not have a PCM. It uses the Motronic M4.4 ECU, not the ME7 of 99-00's and the P2's.

It has an internally regulated alternator.

Is there that much of a difference between the two terms?

[Chuck W]

A '98 does not have a PCM. It uses the Motronic M4.4 ECU, not the ME7 of 99-00's and the P2's.

It has an internally regulated alternator.

Is there that much of a difference between the two terms?

They are completely different systems.

Also, HERE is a thread with posts from @erikv11 on the different types of alternators found in the 850's (and even the '98's). More pics, etc in the thread.

A quick blurb from the thread

I pulled a third VR tonight, it is different, one of the smaller types (Bosch 1197311513).

Here's what I came up with poking around:

The 850 alternators seem to have (at least?) two types of voltage regulator, large format and small format. The alternators themselves are different, with different configurations for connections that correlate with which regulator is contained inside. The best bet indeed seems to pull the regulator, see what style it is, and replace it with the same part number. Otherwise, you may end up with a VR that will not work with the alternator you have.

The "larger" regulators (Bosch 1197311520) shipped on the later 850s. Key features:
- These larger VRs have LRC = Load Response Control. If there is a sudden call for output from the alternator, a reg with LRC will not instantly kick in, and drag down engine rpms. Instead it will kick in gradually over a few seconds. So LRC gives a smoother ride experience.
- This VR also has temperature compensation: output voltage decreases with increasing temperature. This is so the charging doesn't stress out the battery when it's hot.
- These VRs only charge at 14.1 volts, a bit low for some modern batteries (may not charge them sufficiently in the winter, e.g.) but just fine for more budget grade batteries.
- There is a tab connector built into the VR, for the "L" port on the back of the alternator.

There are several part numbers sold on the small regulators (the ones with no LRC, ) and I do not know all the differences (e.g. Bosch 1197311213, 1197311513, 1197311234). But here are some notes:
- No LRC, engine rpm may drop when there is sudden load on the charging system.
- No temperature compensation, they always put out the same voltage
- The small VRs I saw at fcp and eEuro all charge at 14.5 volts, which will be constant since there is no temp compensation. A bit high for most budget grade batteries, when it is warm they may wear them out faster due to gassing (overcharging). But good for some other batteries.
- These alternators do not have an "L" port/terminal, rather there is a "D+" terminal built into the alternator (no connector tabs on the VR). This can help you ID the alternator type.

I'll get a couple pics up to show the differences. There may be other types of 850 alternators, these are the only two I have out and easy to look at. Some of the 98's shipped with 80A alternators, the 850 ones are all 100A.

The crazy expensive VRs seem to priced by some bizarre circumstances, if you buy the Chinese replacement parts they are all priced about the same. If you want Bosch, you may have to pony up the $$. Perhaps Huco is a good alternative.

Since it seems you can't choose just any VR for a rebuild, you might want to grab an alternator that fits the kind of battery you use. For example, I have been buying "Energizer Premium" car batteries from Sam's Club, which are built for a high charging voltage (up to 14.8 V). So I would prefer to avoid the alternators with large format voltage regulators, which only trickle along at 14.1 V or lower. The 14.5 V output of the small ones should be just fine, and charge well in the winter, and a nice Bosch part can be had pretty cheaply.

Lots of voltage regulator specs can be looked up from these sites:
http://store.alternatorparts.com/
http://www.regitar.com/database/
Note: at some sites you must hyphenate the Bosch part numbers e.g. 1-197-311-520 vs 1197311520.

Also found this interesting, for thinking about matching the voltage regulator to the battery type:
http://www.landiss.com/battery.htm

Great resource page for DIY rebuilding:
http://www.rangerovers.net/repairdetail ... .htm#steps

[abscate]

Forest Gump: and that’s all there is to say about that.

[MrAl]

Hello again,

Thanks to all for the great replies and links i think very very helpful.

One of the main concerns of course was does the ECU (onboard computer) actually control battery voltage during charge.
The reason i thought it might is becuase the charge curent/voiltage profile is different than any cars i ever had in the past but of course they were much older than 1998.
For example, in my old 1988 Hyundai when the engine was started the battery voltage would jump up to the highest charge voltage, which was still too low if you ask me, but the Volvo does not do that, it does not jump up for a few seconds, like maybe one or two seconds something like that. So the volt meter reading starts at maybe 12v, then after maybe 2 seconds it climbs up to 14.0 volts and stays there. The older Hyundai would immediately jump up to 14 volts once the engire started.
This led me to think that maybe it was controlled by the ECU, but if it is not (and from the posts here it sounds like it is not) then it just has a slightly more sophisticated voltage regulator, like maybe it checks to make sure there is no short or some other problem before it begins allowing charge current to flow. I also had read that some cars do actually use the ECU to regulate the battery voltage although there may be a default fail safe mode built into the alternator too.

Well i guess i got some reading to do.

The flooded wet cell lead acid battery idea sounds interesting im not sure how to tell the difference though when you go to buy a new battery. Normally i just look for a battery that is specified for this car.

BTW my neighbors car is a Mustang i think year 2002, and it charges at 14.5 volts as measured with a good meter the same meter i use to measure my car when i want accurate voltage readings. It's a 6000 count meter (more common now) and i checked it with a 50000 count $350 USD bench meter, which i checked with a 50000 count $500 USD bench meter. I also have a 4.096 volt standard calibrator which i also use and all the readings agree to within better than 1 percent closer to 0.1 percent.
0.1 percent at 12v nominal means when the voltage reads 12.000 volts it could really be 11.988 to 12.012 volts so it should be close enough. I think it is even better than that though, because when the $350 USD meter reads 12.001 volts for example the $500 USD meter reads 12.000 volts (just for example), and the 4.096 volt calibrator reads 4.096 volts on both meters.