battery choice

Hammer them - voltage set point established. Fourteen point four volts, and que sera sera with the amperage.

More of an issue -by far- is the minimum recommended bulk charging amperage for a absorbed glass mat battery. The OEM has that data and I strongly recommend contacting them and then following their minimum charging rule. No chintzing. This is why I have encouraged purchasing the battery bank with the frwest, thickest plates. Now is NOT the time to weight CCA. Four L-16's with the lowest CCA would have the capability of making even a 3,000 watt inverter catch fire. Forget CCA.

I have encountered numerous brands of AGM battery that are junk. What Lifeline offers, and Rolls and Trojan, is not junk. But on a bank of this size, if I had to pay 300 dollars Canadian to get fewer, thicker plates, with a lower CCA and same weight I would do it in a heartbeat. AGM is a different universe when it comes to CCA. But with heavy cycling AGMs need periodic conditioning. Meaning sacrificing a few thousandths positive plate.

Toss in the following - it is reality...

AGM batteries from reputable OEM are significantly less prone to manufacturing defects. That figure is percentile oriented. But one point that cannot be denied or ignored is the one of probabilities...there is no way to cheat the law of total unit percentage of failure. Thirty-six cells WILL have a higher chance of one or more failing than twelve cells. And before you get your arguments in gear, absorb the fact that AGM L16 batteries are easier to assemble than car jar AGM batteries. Grid misalignment, paste uniformity, and cell connectors are more reliably assembled in an L16. Flat-out, more care is taken with industrial cells than with car jar cells. I chose Lifeline, because I am stuck with car jar size. But Concorde is a prime supplier of AGM batteries of similar ilk to the military. Vendors who fail to supply reasonably reliable mil-spec product are soon banished. In all cases with all types of batteries the industrial battery sizes get more attention and care than a car jar battery. Concorde is the only car jar AGM company that I am aware of that makes an exception to this.

Rolls & Surrette would never represent an inferior product. The only wish I have would be that their L16 have a .175" positive plate. But they don't, so be it. I would want, change that to insist, an investment of that magnitude have a durability lifetime of ten to twenty years.

Rolls Support Desk

"The initial charge current is recommended to be set at I1= 0.25 X C20 (Imax= 0.35 X C20) in order to fully charge the batteries within a reasonable amount of time. It can be set lower, however please be aware that charge time will increase so make sure the batteries have enough time to fully charge before being put back into service. Rolls AGM batteries have a low internal resistance allowing them to be charged at a higher current, therefore faster, than conventional flooded/wet batteries."

... so 35% max., or 140a on a 400Ah bank.

In their user manual, they say 20%... 'because a higher current may result in overheating'. So the concern seems to be mostly about battery temps. Apparently, as long as temps stay below a given temp, a higher rate is fine.

According to Victron,

14. Effect of temperature on charging voltage:

The charge voltage should be reduced with increased temperature. Temperature compensation is required when the temperature of the battery is expected to be less than 10°C / 50°F or more than 30°C / 85°F during long periods of time.
The recommended temperature compensation for Victron VRLA batteries is -4 mV / Cell (-24 mV /°C for a 12 V battery). The centre point for temperature compensation is 20°C / 70°F.

15. Charge current:

The charge current should preferably not exceed 0.2 C (20 A for a 100 Ah battery).The temperature of a battery will increase by more than 10°C (18F) if the charge current exceeds 0.2 C. Therefore temperature compensation is required if the charge current exceeds 0.2 C.

... so again, it appears to be about battery temps.

What I like about the vector charging profile, like that of the vec1093dbd, is voltage rises steadily throughout the entire charge cycle... only to reach the voltage set-point at near full. These lower voltages may very well act as a sort of temp comp, and thus help reduce overheating.

There is definitely minimum acceptable charge current for absorbed glass mat batteries. Discharge a 100 A/H AGM then recharge it at 2 amperes day and night, and repeat. Compare that to a similar discharge then recharging the accumulator at 40% of the ampere hour rate, voltage limited. Count the total of cycles rendered over the battery's lifetime.

AGM presents a quandary if the user does not possess an adequate charger. It is one of the quirks of the AGM battery design.

Exide has this to say about bulk charging agm's:

Charge at a constant current rate of no more than 10 times l20 to a voltage of
14.1V (example; For C20=100Ahr, the max charge current is 10x5A or 50A).

Exide Battery Care

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Sorry PT, didn't mean to hijack the thread... just wanted to lay the old 'gotta go low and slow' bulk charge myth to rest. Enjoy your new batts, whatever you decide on.

Hi,

I've never had a thread hijacked because I don't believe folks offering information are doing so.

AGM low is slow is a poor way to do things. If I did not have the magnum inverter/charger I'd not be going AGM.

I'm still on my quest to run the roof air from solar--but that will be next year. I wish I had not been put in a position where I had to buy a generator. (smelly nasty things requiring maintenance and drinking money).

Thanks, PT.

Well, I just spent about two hours searching for minimum charge rates, only to find a few forum discussions saying 20-30% as a minimum, as per Trojan and a couple other manufacturers... but, of course, 20-30% is the usual maximum quoted. :(

"(smelly nasty things requiring maintenance and drinking money). "

If I had a generator that consumed my drinking money, I'd shoot it...

pianotuna wrote:

...
AGM low is slow is a poor way to do things. If I did not have the magnum inverter/charger I'd not be going AGM.
...

So if all you have is solar, sounds like a higher ratio of Panel wattage to battery Ah is called for with AGM. Are the data sheets saying that not only can AGMs take the high charging amperage, but they prefer it?

And maybe separate issue: are AGMs better or worse at surviving partial charge regimes? For example, first day can only recharge to 90%, second day to 80%, ... , fifth day to 50% and then break camp to find a 120VAC plug. Would AGMs or FLAs survive this better over the long run?

Concorde Lifeline Co seems to insist their product will suffer without it. Driving me nuts. I cannot autopsy a misused AGM to see exactly what transpires with a slow-charged AGM. Might be like eggs. Fry 'em too slow and they'll rip your lips off...