Components on while charging?

shade

Well-known member
He's using a Lifeline for that test, which does say bulk to 14.4v and absorb at 14.4v (@70 degrees F) in their manual.

My Chinese AGMs say right on the case, 14.6v-14.8v bulk/absorb. Going to a higher voltage would alter his test results significantly.

Also the ".2C vs. .4C" is kinda goofy anyway, since those charge rates only apply in the beginning before the CAR starts to drop...which is why he only got a 12min difference over a 5.5hr charge cycle.

Again, going to a higher voltage would have had a bigger impact on charge time. A better comparison than .2C vs. .4C would have been 14.4v vs. 14.7v.
I know Rod is available on forums, but I wish he had a comments section for his articles. Maybe he had a reason for doing it that way, but it's not easy to find out.
 

dwh

Tail-End Charlie
I know Rod is available on forums, but I wish he had a comments section for his articles. Maybe he had a reason for doing it that way, but it's not easy to find out.
There's nothing wrong with it, and it serves to illustrate the two key points he was making...

1. It doesn't matter if you have a 20a charger or a 40a charger (or Optima's 12a or a 200a alternator under the hood) - the battery will dictate the charge rate and even if you do hit the charger's max amp limit...it won't be for very long.

2. Once the charger switches to constant voltage absorb...it's gonna take hours to slog up those last few percents to reach 100%.
 

dwh

Tail-End Charlie
Trojan used to recommend 14.4v for their FLA deep cycle batteries. Everyone did, because it was a nice safe conservative number.

HandyBob came along and said that's bull - you're better off going to 14.8v. Trojan now recommends 14.7v for the FLAs, but still recommends 14.4v for the AGMs.

Odyssey recommends 14.7v for their TPPL AGMs, but Lifeline still says 14.4v for their TPPL AGMs.

Optima's spiral-wound AGMs can goto 15v with no amp limit as long as you don't overheat them.

And, as I said, my Chinese AGMs say 14.6v-14.8v right on the case. I use 14.7v bulk/absorb simply because that's one of the factory presets on my Victron 100|30 charge controller...no monkeying around programming a custom charge profile.


For charging lead-acid - even AGM lead-acid - voltage is more important than amperage, and even so, voltage is not all that critical.

It's not a precise electronic component...it's a chemistry experiment in a plastic box. Most of the time, "close enough" is good enough.

IF you let it charge for enough hours to get the job done.
 

shade

Well-known member
Here's a much longer discussion on charging AGM batteries. I'm still working my way through it, but I'd imagine that Rod's article that I linked earlier has similar themes.

https://forums.sailboatowners.com/index.php?threads/agm-batteries-making-the-choice.124973/

This paragraph seems pertinent to those with low output chargers:

"Don't forget minimum charge current:
Lifeline does stipulate that these batteries ideally need to be charged at a minimum of 0.2C or 20% of rated Ah capacity or you will shorten the cycle life. They will not however quantify the impact of lower charge rates on cycle life. Dave V., the engineer at Lifeline, published a paper and presented it to his peers back in the 90's on current vs. cycle life. Dave's study found that AGM's do need minimum current thresholds in order to get the most cycle life. In short, higher charging currents do lead to longer cycle life with AGM batteries. Odyssey AGM batteries requre .4C or 40% of Ah capacity in charging current as the minimum. While there are many pieces to the cycle life puzzle this is one that I very often see ignored. "
 

dwh

Tail-End Charlie
Yea. Odyssey, as far as I know, hasn't explained why they need that .4C charge rate. My best guess is that their highly pressure squeezed TPPL sandwich needs it to combat electrolyte stratification.

But that's just a WAG.
 

luthj

Engineer In Residence
Higher charge voltages will reduce cycle life in some cases. If a battery spends a lot of time on a charge, using a lower (0.1V-0.2V) voltage improves life, especially for lightly cycled batteries. Hence why most alternators charge at under 14.4V once warm. Deeply cycled batteries, that are routinely so, bennefit from higher votlages. This is becuase partial recharging, and/or sitting at partial charge for extended periods created a MUCH larger reduction in life.

High charge rates tend to break up the sulfation on the plates surface, and also helps to promote porosity, and good grain structure on the cells. Low rates mean denser material being returned to the cathode.
 
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