Alternator overcharging batteries

[Gerald55]

I have 4 AGM batteries in my rig with a total capacity of 440AH (actually 880AH @ 6V, but of course they are wired to get 12V).

The data sheet for my Haze batteries species a bulk -> absorption cutover point of 14.4V. Both my solar charge controller and my progressive dynamics converter are smart and can get close enough to the required profile, so I don't have many concerns there.

The alternator charging, however, is "dumb". As far as I understand it, an alternator is a voltage source, and seems to put out about 14.3V or so. So when the batteries are charging on this source, during a long drive, for example, will the alternator overcharge the batteries?

Also, will the 4 batteries accept 4x more current than the 1 battery that came originally in my coach, and will this put undue strain on the alternator?

[pianotuna]

Maybe this summer I'll finally use something like this:

https://alternatorparts.com/quicktifier-external-bridge-rectifier.html

[pianotuna]

Hi Robert,

I quite often see my solar sending power to the engine. I do have control of the charging circuit relays. I figure I get a bit of savings and it eases the load on the alternator.

[mchero]

Don
Cant give you a solid answer on that one. I was originally looking at a Balmar 3 stage alternator but never got as far as pricing. I do see that their regulators can run anywhere from $200 to $300.
I recently installed 1K of high voltage panels with a Morningstar 200 light charge controller. I'm still thinking about adding a relay circuit to the Morningstar that will disconnect the aux start relay while driving down the road "IF" I have enough solar.

Brett would have more experience with the Xantrex regulator.

[pianotuna]

Is the Xantrex Alternator Regulator a replacement for the OEM or can it be used at the same time as the OEM regulator?

mchero wrote:
How about something like this?

[wolfe10]

mchero wrote:
How about something like this?

An excellent unit. Have one on the sailboat. May be overkill on a motorhome, but on a boat where an engine can be running for 24 hours at a time or the opposite (engine just run for charging batteries) a smart regulator is a big asset.

[mchero]

How about something like this?

[RCL]

If your two banks of batteries(house and chassis) batteries are charged through a diode isolator there is one scenario that I haves experienced. In my case, the alternator output was determined by the voltage seened at one bank. This method adjusted the alternator output to compensate for any resistive drop in the high current charging line to that battery. It turned out that the chassis battery line had a bad crimp connector in it.The alternator upped the output voltage to compensate, but the house batteries saw this higer voltage and were cooked. This was on my '83 Southwind.
Dick L

[Gerald55]

I'll be boon-docking pretty much everywhere between Mexico through Colombia, so I expect high temperatures to be the norm. I'm thinking my manual disconnect for the charge line is a bare minimum for that kind of weather.

[MEXICOWANDERER]

Wuuwee first time I've noticed this thread 🙂

Yep, MoPar does indeed have ECU Voltage Irregulators.

To cure the long long week's long vacation hotfoot, remember a silicon rectifier drops voltage automatically by roughly point seven .7 volt. A standard 70 amp three bolt finned isolator tolerates 140 total amps when BOTH OUTPUT STUDS are paralleled. This goody would be installed near the batteries. The regular incoming voltage cable would go to the center terminal and BOTH outboard studs would be bridged and pass into the AGM positive stud.

Dropping voltage by .4 volt is a little trickier. It requires passing the alternator - AGM charge lead line through an adequately sized SCHOTTKY rectifier. Ambulances use isolators with Schottky rectifiers but if you should price one you may end up inside the ambulance.

This gets even funner....

14.2 volts is far too high if battery temperature is say 90F. A standard silicon rectifier isolator would do the trick just fine. If you want to get boondocker fancy wire in a switch with appropriate gauge cabling that bypasses the isolator with the flick of the wrist.

GYRO GEARLOOSE TYPES
Re-read this post AGAIN. CAREFULLY before you unleash with ISOLATOR DIATRIBE. This is NOT a standard silicon rectifier isolator hookup. Questions I will answer politely. Criticism gives me license to bite with needle fangs filled with sarcasm venom.

I am doing this precise thing with a psychotic WFCO. Only with a 500 ampere rated Schottky rectifier. But the Schottky rectifiers sold on eBay need to be insulated and heat sinked and fitted with bolt terminals and case and forget it - it's not a project suitable for novices.

An isolator with switch makes perfect sense for full day after full day on the road. If the days include high heat I would rate the modification as "essential".

FURTHER NOTE. THINK BEFORE CRITICIZING
Converter, solar, squirrels in a cage charging gets connected BETWEEN the isolator and battery.

Gripe, Snivel & Whine...

14.3 volts is too high of voltage for an antimony flooded battery. 14.3 volts combined with hot summer temps and marathon driving BOILS flooded batteries. Yeah! Gurgle Gurgle. This is why I shook my head at all the neurotic grade micro-management of converters, solar yadda and this subject was not touched upon.

Not everyone fits into the marathon hot weather driving scenario. But those who do can be battery killers ESPECIALLY WITH RV FLOODED BATTERIES.

And for the short-term memory types this is regarding vehicle engine alternator charging ONLY.

[Gerald55]

full_mosey wrote:

Gerald55 wrote:

...
OK, the need for high amp recharges was news to me. Or is this basically another way of saying that AGMs do need equalization? ...

No. Equalization is a flooded(FLA) thing; meaning to use excess VOLTS to force electrolysis so that the stratified acid is re-stirred EQUALLY throughout the liquid.

Well, not anymore. When AGMs were just penetrating the market, the conventional wisdom was "don't equalize", but that's been changing. Today, several (most?) of the top-line AGM manufactures recommend some type of equalization. Often it seems to be a "vent-less" type of equalization - i.e., not gassing enough to pop the vents on the AGM, so no electrolyte is lost.

In any case, it's clear that some of the benefits of equalizing carries over from flooded LA to VRSLA AGM as well.

As to 'the need' for high Amp charging, there is partial truth to that. The lowest actual mfgrs spec I have seen is to limit Amps to 30% of the 20hr rating. The highest I have seen is unlimited Amps. Some of this is lawyer talk and some is marketing talk.

OK, but that only seems to support the idea that charging too fast can be a problem, not that charging too slow can be?

AGMs do benefit from temp comp chargers. These chargers limit Volts by reading the battery temperature via a probe. IMHO, the purpose is to maximize Amps while at the same time keeping Volts below electrolysis. Allowing electrolysis is simply a waste of energy in an AGM and results in slower charging.

Yes, I use a temperature probe to enable temperature aware charging in my setup.

[landyacht318]

Don, my Mopar voltage regulator inside the engine computer bounces around from 13.7v to 14.9v devoid of any logic or reasoning, as far as I can determine. Soon I hope to bypass it and have a potentiometer on my Dashboard.

Lifeline AGM says when deeply cycled, a 20%, C/5 rate is the minimum initial recommended charge current. 20 amps per 100Ah battery.

Odyssey says 40 amps minimum.

Mex has previously stated that these high charge rates when depleted force acid migration through the glass matting, IIRC.

I am quite happy with my Northstar AGM's abilities to both accept and release current. Its 90AH total capacity, cranks my engine easily even at 66AH from full.

But I have to feed it those high amps(25+), and regularly bring it upto 14.46 volts until amps required to maintain 14.46v taper to 0.42, and sometimes the amount of time required to taper to 0.42 is rather obscene.

The longer in between 100% full charges, the longer the tapering stage lasts, and can be longer than the daylight available this time of year, even if I were to reach absorption voltage at 9am.

I doubt I could keep this battery happy on Solar and Alternator alone in my usage, certainly not in winter anyway.

Lifeline's 'conditioning' procedure is similar to a flooded battery equalization procedure. Like equalizing, it should not be initiated until the battery is as 'full' as it gets after a regular charging sources goes through the motions, holding proper absorption voltage for 2 to 4 hours.

The High amp recharge requirement of AGMs is not directly relatable to an Equalization charge on flooded batteries as far as I know.

I've noticed when my Northstar is full, it takes 0.0x amps to maintain 13.6v, when I temporarily crank up the voltage to 15v when it is already fully charged, amps also taper to 0.0x amps within a minute. Same with 15.3v but I have not pushed it higher than that. I've noticed no capacity loss and have not done anything remotely resembling Lifeline's conditioning procedure. It gets 40+ amps from an adjustable voltage power supply, sometimes in combination with a 25 amp schumacher, and my alternator can also provide 105+ amps to it.

I like having a battery which can enjoy these rather extreme charge currents, as opposed to tolerating them.


Also note the less expensive AGMS say to limit current to NO MORE THAN 30 amp per 100Ah of capacity, while the high Dollar AGM's can handle practically any huge number thrown at it, and laugh.

I assume 40 amps into such a battery depleted to 50% would exceed the recombination abilities of the battery, and the vents would open.

[full_mosey]

Gerald55 wrote:

...
OK, the need for high amp recharges was news to me. Or is this basically another way of saying that AGMs do need equalization? ...

No. Equalization is a flooded(FLA) thing; meaning to use excess VOLTS to force electrolysis so that the stratified acid is re-stirred EQUALLY throughout the liquid.

As to 'the need' for high Amp charging, there is partial truth to that. The lowest actual mfgrs spec I have seen is to limit Amps to 30% of the 20hr rating. The highest I have seen is unlimited Amps. Some of this is lawyer talk and some is marketing talk.

AGMs do benefit from temp comp chargers. These chargers limit Volts by reading the battery temperature via a probe. IMHO, the purpose is to maximize Amps while at the same time keeping Volts below electrolysis. Allowing electrolysis is simply a waste of energy in an AGM and results in slower charging.

Maximum voltage 15.6 volts. No current limit as long as battery temperature remains below 125°F (51....

HTH;
John

[Gerald55]

landyacht318 wrote:

Also, solar cannot meet the higher amp recharge requirements they need every so many deep cycles.

My Northstar AGM protests at 4 cycles of only low and slow solar, even if it meets the acceptance threshold each day. One high amp recharge and it returns to happy. My alternator is cheap and is easy for me to replace, so I use thick copper and do not fear maxing it out as it is cheaper than a new battery.

OK, the need for high amp recharges was news to me. Or is this basically another way of saying that AGMs do need equalization? I think equalization was more about higher voltages for a longer period of time (on a nearly full battery), than "high amp" recharges from a heavily discharged state, so I'm not sure it's the same thing.

I'm not an expert yet, but I have read a lot about LA chemistries in general and AGM in particular and didn't run across much discussion of that.

Agree that alternators are cheaper than new batteries. In my case, however, I'll be boondocking for 1+ years in third-world countries where parts, even alternators, may be difficult to come by and a failed alternator pretty much means your rig is dead in the water. A shorter battery lifetime, on the hand, may cost more $, but is less likely to leave you up the proverbial creek.

[time2roll]

What is the measured house battery voltage at the four hours mark while driving?
Measure right on the house battery terminals.
AFAIK most alternators drop voltage as they heat up.

There is no real undue strain on the alternator. JMHO.