Bank These Batteries? UPDATE

"means usually getting the big one down to 50% while there is still lots left in the inverter's bank"

Certainly a 50% discharge is talked about mucho on this forum but its just a convienent number. Trojan for instance says on their Signature Flooded Line including T105, T125 and T145 that if you discharge to 50% you can expect 1,250 cycles but if you only discharge to 60% you can expect 1,500 cycles....almost an extra year of camping. I'd keep them separate, protect the most expensive battery first and switch when you get to a 60% SOC.

You'd have to shut your system down for 24-hours to do the following.

1. Guaranteed hit-the-wall recharge everything.

2. Discharge to around 50% SOC

3. Disconnect between battery types

4. Measure voltage potential each battery after 24 hours disconneced

Seems they will be fine while in use or on a float charge.
Disconnect if storing with no float.

(opinion only)

Got them at hit the wall fully charged separately and on their Floats. I am always on a Float charge at home. Right now I float them separately but to the same voltage--13.8 with a temp adjustment if really hot or cold.

So next step would be to bank them and discharge to about 50%. My bank wiring would be the two 100s as a 200 in parallel with the 250 for 450 and put load/charge across between the 200 and 250 via Trimetric shunt for negs.

Discharge at 22.5a (20 hr rate) for about 10 hours and stop when AH are down 225. Disconnect all three and let them sit for 24 hours and check the three voltages.

What would it mean if they are not the same? How different is too different?

I can bank them today, do the 10 hr tomorrow, and the wait day Sunday, get the voltages Sunday evening.

I did not follow the links but as SMALL differencer in voltage during the Bulk/Absorption statges would not scare me off. The float is the same and batteries in parallel form a "power commune" each according to its ability each according to its need.

wa8yxm wrote:
I did not follow the links but as SMALL differencer in voltage during the Bulk/Absorption statges would not scare me off. The float is the same and batteries in parallel form a "power commune" each according to its ability each according to its need.

I am more worried that the big 250AH might be more of a "floating/standby" type, and not be able to take high amp discharge (MW on inverter) or high amp recharging so well as the two 100AH batts, that can take that (as proven in service).

If banked, of course they share everything, so the impact on the 250 would be less than by itself. Yes, they share in proportion to their sizes in AH and will all keep the same voltages and SOCs while banked.

I would be giving up the advantage of being able to run down the 250 "house batt" and still be able to run the "inverter batt" without setting off its low voltage alarm (which is a real advantage), but OTOH, I have been with the 250 down to 50% and no way to recharge it right away, and still have bags of AH left in the inverter's bank, but unable to use those as wired up with no connection to the "house" 12v stuff.

I do have an extra couple of Wet 12v 27s to take along for extra house work to add to the 250 same as I did with the two 6s as "house" if the forecast is for no solar, but that is a pain. Six batteries.

I am looking at banking the three AGMs instead as a possible way to "get it all", with no solar for four or five days before going home. (No generator or shore power)

It has turned out that the typical AH usage makes this look possible, so I want to know if banking the AGMs is at least an option.

---I am adding to Mex's steps, that now they are all disconnected and charged up, I will leave them off Float like that till tomorrow and then get their resting voltages when full, to add to the later data of their resting voltages after being discharged to about 50%. Might mean something, and easy to get.

This might be a time for me to get one of those 1,2,Both switches some guys here swear by.

me.. i would connect them all together
use as one bank charge at 14.4v
top charge at 14.8v

float at 13.8v

MrWizard wrote:
me.. i would connect them all together
use as one bank charge at 14.4v
top charge at 14.8v

float at 13.8v

I am kind of hoping that will work. I will still do Mex's procedure next couple of days to see if there is a problem arising from that.

I would still have the two solar sets (one 255w and three 100s) but would then put both controllers set to the same voltage on the one big bank. I could reduce to one converter.

No generator with the MH. (Just solar and alternator) So no 50-90s like before with the 5er doing 155 amps with a 55 and a 100 amp PowerMax. Only do charger at home with lots of time, so lower amps is ok.

The 100 pops a stick house breaker so likely just use the 55. (The 75 ADJ still does any 16v work like with the spare extra Wet 27s--that 75 is the only charger I have that can do over 15.5v.)

I am getting quite a collection of gear that still works I don't need anymore with the MH and no 5er or TC anymore. There might be a garage sale in my future! :(

With AGM there should be near zero transfer. .15 volt difference is excessive. The high will be feeding the low to balance. When is operational stasis if that much potential is evident, grab your DMM set it for 10-amps and then find out how many milliamps are draining. Check it again an hour later. Imbalance still there?
what this "proves" is differences in chemistry. The closer the batteries pencil out the batter they will get along during the charge and discharge cycles as well as float.

Got the 10 hr test started. Maybe a problem already? I disconnected the three batteries yesterday after they were on their Floats, but this morning they still had a bit of surface charge it seems, so their voltages were not the same when I banked them to do the test. I had the 6G disconnected a little earlier than the other two.

6G - 13.16, Stark 1- 13.26, Stark 2- 13.22 by multi-meter. Banked it was 13.2 on Trimetric before 22.5a load applied. (at which it dropped to 12.6 "loaded")

Hope that won't matter for the final voltages after the 24 hr rest at 50%. Expect early individual 50% voltages this evening and finals Sunday evening.

A day sitting at 50% before recharging is not going to kill them. (If it does, they deserve to die!)

Another sign of ? is that when in parallel and on their recharges from the last trip and then on Float, the two Starks were at different temperatures. 22C vs 25C, eg, with Stark 2 the higher. Kept the 3C diff at different temps.

EDIT- battery temp is 15C both Starks at near 75% SOC. At 15C capacity is 95% of rated. 427 so my target is 214AH down. So my 22.5a is a bit high for the 20hr rate for that of 21.3 so must reduce to that or a bit lower to average out.