acceptance charging rate AGM batteries
Hi all, It is generally thought that acceptance rate for a flooded deep cycle battery is about 12.5 amps per 100 amp-hours of capacity once the bank is at 85% state of charge. I know that accept...
Forum Discussion
Hi BFL13,
Nothing is ever simple with batteries. Finding two identical batteries or even cells is on the same order as finding two identical snow flakes. It may happen, but it is rather rare.
I'm using surplus acid AGM so I have some "extra" parameters that I have carefully researched regarding maximum voltage for bulk, and for float. I also know that c/5 is the maximum safe recharging amperage. I do not exceed either. I do know the OEM resting voltage when new, but being full time that is a not too useful number.
I do know that resting voltage for AGM is 5 to 8% higher than for flooded jars, as a rule of thumb.
For the purposes of discussion I'm suggesting that the charger can be of infinite capacity from a supplied amps point of view. I want to know at what percentage of fully charged the AGM jars start to "push back" as flooded jars do above 85%. I know it is higher than for flooded.
I'm using Mex's "rule of thumb" of 1% amp rate equaling charged to 100%. In my particular case that means 5.56 amps.
Flooded are a different kettle of fish because electrolyte loss via gassing can be dealt with by adding distilled water. So "extra" voltage to force faster charging causes some extra plate shedding. I believe there is little to be gained, charging wise, by "hitting" the flooded jars with high voltage unless you are trying to equalize the cells. Equalizing can be done at the c/20 rate with high voltage. Doing that may reduce shedding.
Doing high amps (over 12.5 amps above 85% state of charge) may cause lots of extra gassing and heating. I think part of that is the higher and higher internal resistance as the flooded cell approaches 100% state of charge. The "pipe" becomes smaller and smaller and increasing the "pressure" with higher and higher voltage is a bit futile. But that is not the focus of this thread.
No doubt, there is gassing within an AGM, but so long as there is no venting to the atmosphere, all is well, because of the recombination of the hydrogen and oxygen within the case. I suspect that happens after charging has stopped.
Nothing is ever simple with batteries. Finding two identical batteries or even cells is on the same order as finding two identical snow flakes. It may happen, but it is rather rare.
I'm using surplus acid AGM so I have some "extra" parameters that I have carefully researched regarding maximum voltage for bulk, and for float. I also know that c/5 is the maximum safe recharging amperage. I do not exceed either. I do know the OEM resting voltage when new, but being full time that is a not too useful number.
I do know that resting voltage for AGM is 5 to 8% higher than for flooded jars, as a rule of thumb.
For the purposes of discussion I'm suggesting that the charger can be of infinite capacity from a supplied amps point of view. I want to know at what percentage of fully charged the AGM jars start to "push back" as flooded jars do above 85%. I know it is higher than for flooded.
I'm using Mex's "rule of thumb" of 1% amp rate equaling charged to 100%. In my particular case that means 5.56 amps.
Flooded are a different kettle of fish because electrolyte loss via gassing can be dealt with by adding distilled water. So "extra" voltage to force faster charging causes some extra plate shedding. I believe there is little to be gained, charging wise, by "hitting" the flooded jars with high voltage unless you are trying to equalize the cells. Equalizing can be done at the c/20 rate with high voltage. Doing that may reduce shedding.
Doing high amps (over 12.5 amps above 85% state of charge) may cause lots of extra gassing and heating. I think part of that is the higher and higher internal resistance as the flooded cell approaches 100% state of charge. The "pipe" becomes smaller and smaller and increasing the "pressure" with higher and higher voltage is a bit futile. But that is not the focus of this thread.
No doubt, there is gassing within an AGM, but so long as there is no venting to the atmosphere, all is well, because of the recombination of the hydrogen and oxygen within the case. I suspect that happens after charging has stopped.
BFL13 wrote:
I think the question is complex, so my answer was incomplete.
The 12.5a at 85% per 100AH marker needs to have a voltage specified, but of course that battery voltage would still be rising on the way to a higher charger voltage (Vabs) going through 85%.
I use this type of marker to judge when to shut off the generator at about 90% SOC doing 50-90s. My rule of thumb is 5 amps per battery, so I watch the Trimetric amps (or Vector charger amps read out) and for four batts that is 20amps. That was for 14.4ish and I now charge at 14.8, so in fact I could stop sooner at some higher amps now.
So the question is, for an AGM, what is the marker for doing that same thing? You need to specify the charger Vabs, and then ask what would the amps be at 85% for a 100AH AGM, assuming the charging amps is higher than what the marker amps would be.
Eg, in that 12.5a per 100AH case, a 10 amp charger would go past 85% before amps tapered, so you would only see that at 85 if you used say a 15 amp charger or higher.
I don't know if that would be higher or lower amps than 12.5 for an AGM. It might relate to the higher resting voltages per SOC of an AGM.
With no AH counter, which would make it a lot easier, you could run a few trials and note the resting voltage after different marker amp amounts. This would give you a rule of thumb amps amount to stop the generator recharge at near your desired SOC. (50-80, 50-90, etc)
