Sizing battery charger for AGM and Generator On-the-hook

[rgleason]

Originally Posted by john61ct

FLA is a low-CAR chemistry, even deeply depleted cannot accept much more than .15C, and even that falls off sharply after CV transition.

That's why besides fitting sideways, minimizing charger runtime is a valid compelling reason to go to high-CAR AGM.

Upside to FLA is you don't need a huge charger to maximise longevity, and they inherently live longer, more robust anyway. And cheaper.

Now maybe the pricey Rolls / Surette units are somehow tweaked to accept higher rates, dunno.

CAR = "Charge Acceptance Rate"

I thought FLA = .25C Acceptance according to Balmar for sizing.
and AGM = .40C Acceptance for sizing the Alternator.

You are saying .20C is the maximum for longevity.
225ah x .20 = 44 amps rather than 56 amps.
So if SOC 50% = 112.5 amps and

bulk mode is .3C= 67.7 is going to be an 1.5 hours at 44ah
bulk mode is 1.2 hours at .25C = 56 amps charging.

In bulk mode, as in absorption mode, isn't the battery calling all the shots, and the alternator/regulator is just providing the current accepted, controlled by the regulator and temperature sensors?

[ranger58sb]

Originally Posted by rgleason

CAR = "Charge Acceptance Rate"

I thought FLA = .25C Acceptance according to Balmar for sizing.
and AGM = .40C Acceptance for sizing the Alternator.

You are saying .20C is the maximum for longevity.

IIRC, Lifeline recommends .2C and Odyssey recommends .4C as MINIMUM for best longevity.

-Chris

[john61ct]

Originally Posted by rgleason

I thought FLA = .25C Acceptance according to Balmar for sizing

Sure according to bigger is better, but they won't actually accept that.

Alts are rated at maximum, real life is 50-70% output.

> AGM = .40C Acceptance for sizing the Alternator

Because they don't make any bigger.


> You are saying .20C is the maximum for longevity.

Not at all. Re-read what I said, and discuss one chemistry at a time.

Bulk means source is delivering maximum it can. With a weak source or high-CAR bank, that may be well below what the bank could accept.

Once setpoint V is reached (Absorption) regulator holds to that as max V, and then eventually over time amps declines.

You can't generalize amp rates at SoC / time spent between the two stages, too many variables.

Measure and chart them for a given bank and charge source, sure.

[rgleason]

John,
I am going to stop this dialog. It never seems to get resolved or confirmed.
Thanks for all the help.

[a64pilot]

Just remember when your sizing leave enough room if you will for your house loads, they come off of the top, mine can be higher than 15 amps.
Then if an alternator maybe size for understanding you don’t get max power continuously, you may get well less.
However it seems a good shorepower Charger will give continuously 100% of its rated output, so my 125 amp Magnum is bigger than my 165 amp alternator, pretty much twice the output.

I do agree that there is a point in sizing that it’s just wasted excess, it’s not going to hurt, it’s just not going to be used.
I could have modified my boat to get to 50 amp service, bought a 5.5 KW generator as opposed to a 3.5 and gone much bigger on my chargers, but it really wouldn’t have been used longer than just a few minutes each day, and does not shorten charge times enough to matter, but would have been a lot of work, and a lot of money for no real benefit.

[john61ct]

Yes those C rates above are actual power output not max rating, and available to the batt for charging, after concurrent loads.