AGM Charge Rates and Times

This topic gets confusing as to what is being talked about.

1. If you put a 40a charger on an AGM or a Wet at 50% SOC you are going to get 40a either way.(Except in 3, below.) Roughly the same profile

2. Can the AGM accept more amps than the Wet if you had more of a charger?

3. The curious case where Mex mentioned that an AGM at 13.8v has a higher acceptance rate than a Wet at 13.8v, so in that case, if the Wet at that SOC is only accepting 30a then the AGM at the same SOC and voltage would accept more amps than that (not sure how many more)

So you could get faster charging if you had more amps--but that is true of both types. You can get faster charging with an AGM at the same voltage if your charger can do the extra amount above what the Wet will accept at that voltage.

I can try and test the 13.8v acceptance on my Group 27 Northstar AGM versus my Screwy flooded 31.

From previous cycles of both, I can notice that when I set the MW voltage to 14.9v and let my Meanwell dump 41 amps into either. The Voltage rises faster on the flooded battery, and once battery voltage approaches 14.5v amps start tapering.

But it is not an even test as the AGM is 90 AH and the Screwy 31 claims 130AH, and now has over 330 deep cycles on it and the AGM, perhaps 30.

I do notice my AGM can accept more alternator amps than the flooded battery can. The larger flooded 31 tops out at about 75 to 80 amps when depleted, the Smaller Northstar AGM-27 will take 105a when my alternator belt starts squealing, so I don't really know how much it can take when depleted. Somewhere north of 105amps.

All I can say definitively is, is that my NS AGM cranks my engine faster, and holds higher voltages the next discharge cycle the higher the recharge rate is.

Odyssey AGM says a minimum of 40 amps for their 100AH group 31 when deeply cycled. So no low and slow solar recharge with these, if you believe their engineers. Northstar makes many similar claims as to performance and lifespan as Odyssey, so I've been using this 40% charge rate as the minimum for my NS AGM, and only cycle it deeply when I have grid power to run my MeanWell, or enough driving to do so that my alternator can quench the depleted battery at a high rate at least until the point where amps start tapering below 30.

I also have been making sure I only stop 14.7v after amps to hold 14.7 drop below 0.4a, and I have seen it take as little as 0.2A to hold 14.7v.
This Northstar battery has a rested OCV of 13.06v, and it held that for 3 weeks when I flew cross country for the holidaze.

I know this minimum high recharge rate does not float many people's boats. I'll believe the manufacturer and my own observations.

Seeing is believing. Three dollars per amp hour for a stupid group 31 that can take 100+ amperes charge rate is mighty enticing. As far as the need for floating is concerned AGM requires <15% of the energy it takes to maintain a flooded battery.

I tell meself if I ever get so lazy I cannot devote a few minutes a day for RV "chores" then that's the day I hang up my spurs, check into a hotel and ring room service. The valet will fetch my suit, steam out the wrinkles and demand the bidet contain perfumed water.

I cannot help but wonder how some of you would have handled a bit and bridle, a burlap sack of grub, cowboy coffee, flatbread and beans in the morning?

The poster who travels to central america is different. He faces challenges beyond your imagination. But dragging a luxury apartment into the woods seems a bit much. You can't get away from it all if you take it all with you. Maybe I have indeed become totally obsolete.

MEXICOWANDERER wrote:
Maybe I have indeed become totally obsolete.

Nah, different people just like to do stuff different.

mena661 wrote:

MEXICOWANDERER wrote:
Maybe I have indeed become totally obsolete.

Nah, different people just like to do stuff different.

Yeah but like it or not there is only one "reality". Folks can rationalize whatever tickles their fancy, to death. Re: lead acid batteries, when those folks start skewing reality trying to bend other people's elbows is when I arch an eyebrow.

HERE IS A REALITY FOR RV SIZE BATTERIES

$2.00 PER AMP HOUR STANDARD FLOODED LEAD ACID

$5.00 PER AMP HOUR AGM BATTERY

$22.00 PER AMP HOUR (@) LIPO BATTERY

Think before you leap at my costs per ampere hour.

You can get LFP pre-packaged for $10 per amp hour. Less if you DIY it.

http://elitepowersolutions.com/products/product_info.php?cPath=27_49&products_id=241

And that system comes with a charger too.

(Jacques Clouseau)

"And another thing"

Muse the 20 amp hour rate life-cycle testing protocol

5, 000 cycles. Each discarge cycle should be 20 hours in length. TIME affects battery life. It is an
Intregal component of battery degradation.

5, 000 x 20 you do the math. Remember recharging time is NOT factored here. Only time spent discharging.

C'mon. You do the math. One hundred thousand hours. How many YEARS is that? For one test.

As Charlie Chan used to quip...

"Not born yesterday...

Born day before.."

MEXICOWANDERER wrote:
HERE IS A REALITY FOR RV SIZE BATTERIES

$2.00 PER AMP HOUR STANDARD FLOODED LEAD ACID

$5.00 PER AMP HOUR AGM BATTERY

$22.00 PER AMP HOUR (@) LIPO BATTERY

Think before you leap at my costs per ampere hour.

I think a T -1275 is rated to use 75 amp hours to a 50% SOC, and they are $225 to $240 each. Trojans and Lifelines are not on that price per amp hour scale unless you are sporting only the GC-2 6V batteries.

Of course, Old Scrounger here did get a pair of freebie T-1275s, so a cost of $0 is a lucky wild trump card.

MEXICOWANDERER wrote:

5, 000 cycles. Each discarge cycle should be 20 hours in length. TIME affects battery life. It is an
Intregal component of battery degradation.

5, 000 x 20 you do the math. Remember recharging time is NOT factored here. Only time spent discharging.

C'mon. You do the math. One hundred thousand hours. How many YEARS is that? For one test.

As Charlie Chan used to quip...

"Not born yesterday...

Born day before.."

Check out the DIY EV forums. Those guys have been getting ~2000 cycles from their LFP batts. That's fully charged and discharged (80% DOD) with anywhere from .3C to .5C charge/discharge rates.