AGM Mystery Capacity Crash Below 75% SOC UPDATE
Update 28 Sep.
I had an issue with one of my AGMs last Spring where it seemed to act well until all of a sudden it crashed under load when below 75% approx. Now they are all doing it.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29883938.cfm
I decided to wait till Fall to do anything about it all. Well, the other day while camping with the whole bank of 450AH worth (as rated--not actual amount now) everything went well at first--high amp draws on MW, kettle, and toaster, no problem-- until:
Morning voltage 12.7, indicating approx 75% with these batts according to spec sheet, and ran the kettle (90 amps) three times within an hour or so (coffee), no problem with voltage drop or anything, and then toaster 70 amps, and poof! Voltage drop crashed to big amount, inverter quit. Yipes. BUT-- voltage then bounced back to 12.7 and we still had "12v" for all the usual stuff in the RV no problem.
That day, got the batts nearly full via generator and solar and then all the high draw things worked again no problem. Until next morning, same thing again.
A few kettle runs (voltage drop 0.7v each time to 12.2--as low a drop as it ever was when all new, so perfect as the baseline) and then poof! Voltage drop crashed next time, and that was that. Except bounce right back to 12.7 (supposedly about 75% SOC with these batts--and AH count confirmed by -90AH from whatever the capacity really is of the 450 rated.)
And again after that we still had 12v ok at normal low RV voltages for all other things rest of the day--just no high draws allowed.
Ran some tests at home today, and all three AGMs are doing this. Act perfectly with low voltage drops until down to about 75% and then they can't handle high amp draws, but still can do low amp draws.
The change-over is not gradual, but is a drop off a cliff kind of thing for the high amp draws. Ok at low amp draws.
Back when I had old and tired Wet batts, at some point they got so low in capacity (SOC), they could not do the high amps at lower SOC (say 65% instead of down to 50% as before they got tired) without hitting the inverter low voltage. BUT this is way different. There is this sudden crash.
What does it all mean? What has happened inside these AGM batts that makes them do that? (I am not asking what to do, but just want to know what the heck is going on)
Thanks.
PS--I will not attempt the Lifeline recovery thing Mex mentioned in the linked earlier thread. Too scary! And these are not Lifelines that are stronger built than most other AGMs either. So I will toss them if I need to before trying that, even if it would work maybe.
I had an issue with one of my AGMs last Spring where it seemed to act well until all of a sudden it crashed under load when below 75% approx. Now they are all doing it.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29883938.cfm
I decided to wait till Fall to do anything about it all. Well, the other day while camping with the whole bank of 450AH worth (as rated--not actual amount now) everything went well at first--high amp draws on MW, kettle, and toaster, no problem-- until:
Morning voltage 12.7, indicating approx 75% with these batts according to spec sheet, and ran the kettle (90 amps) three times within an hour or so (coffee), no problem with voltage drop or anything, and then toaster 70 amps, and poof! Voltage drop crashed to big amount, inverter quit. Yipes. BUT-- voltage then bounced back to 12.7 and we still had "12v" for all the usual stuff in the RV no problem.
That day, got the batts nearly full via generator and solar and then all the high draw things worked again no problem. Until next morning, same thing again.
A few kettle runs (voltage drop 0.7v each time to 12.2--as low a drop as it ever was when all new, so perfect as the baseline) and then poof! Voltage drop crashed next time, and that was that. Except bounce right back to 12.7 (supposedly about 75% SOC with these batts--and AH count confirmed by -90AH from whatever the capacity really is of the 450 rated.)
And again after that we still had 12v ok at normal low RV voltages for all other things rest of the day--just no high draws allowed.
Ran some tests at home today, and all three AGMs are doing this. Act perfectly with low voltage drops until down to about 75% and then they can't handle high amp draws, but still can do low amp draws.
The change-over is not gradual, but is a drop off a cliff kind of thing for the high amp draws. Ok at low amp draws.
Back when I had old and tired Wet batts, at some point they got so low in capacity (SOC), they could not do the high amps at lower SOC (say 65% instead of down to 50% as before they got tired) without hitting the inverter low voltage. BUT this is way different. There is this sudden crash.
What does it all mean? What has happened inside these AGM batts that makes them do that? (I am not asking what to do, but just want to know what the heck is going on)
Thanks.
PS--I will not attempt the Lifeline recovery thing Mex mentioned in the linked earlier thread. Too scary! And these are not Lifelines that are stronger built than most other AGMs either. So I will toss them if I need to before trying that, even if it would work maybe.
