Batteries have begun to fail

[Wolvenar]

So you have 12 volt batteries, two in series.
You still have 12 cells in series essentially no matter how you wire it externally.
Either that or you are not 24 volts?.?
Seems you have a lot more wire involved and if that's true, it's possible that it could mean more losses.

I have never had troubles with batteries being in an unequal SOC.
My problem is likely that these things are already a couple years past what most think of as their normal life span.

[Wolvenar]

Ah ok looking at this with a decent monitor and not a phone, I see the entire thing. Your wiring is not quite what I thought, any which way its still 12 cells in series.

[ChrisOlson]

Yes, no matter how you do it, you always have the same number of individual 2 volt cells in series to make a certain voltage (in this case, 24 volts).  And every cell has to deliver the same amount of amps, no matter what the system voltage, for a given load.  The big six cell 12 volt batteries eliminate external series connections and the voltage drop and resistance in wires associated with them.

The cells in a multi-cell battery are manufactured together as a unit.  In my experience with them, there's less difference between cells in the multi-cell battery than you have between two different batteries.  That's why I prefer using the big 2.4 kW 12 volt batteries vs 1200 ah 2 volt cells.  Rolls manufactures the T12's with the same plate specs as the big 2 volt cells, and they have the same 7 year warranty for off-grid use.

Most of the extra wires in my bank are for balancing and they carry very little amps.  The high amp wires are the series connection wires and the wires from each bank to the bus.  All the paralleling simply keeps things balanced so voltage between individual batteries doesn't get out of whack under extreme loads, and no wire in the bank ever carries more than 60 amps with the inverters pulling 360 amps.  Using the 12V batteries keeps the total length of wire carrying that 60 amps to a minimum.  If I had twelve 2V cells in series to make 24 volts, every series jumper from cell to cell has to carry that full 60 amps.  With the 12V batteries I only have one external jumper.  All the other jumpers are internal with direct connection to the plates.

When we bought our inverters the guy I got them from, that's been in the RE business for 32 years, told me that our bank was going to be woefully inadequate to run those inverters at full load.  I shrugged it off.  Two weeks later I was back to buy batteries.  He had 2 volt cells and 6V in stock and he recommended not using those.  He had to order the T12's, but he said it's what we need if we want to run at full capacity and not have problems with the bank.  That Rolls bank cost us $10 Grand but in the end the guy was right.  It's been over a year, we run our inverters at full capacity on a regular basis, and not a single problem with any of the batteries.

When we first got the batteries I hooked them up two in series and then paralleled all the series strings.  Within a short time we had batteries .25 volts off from nominal.  The guy drew the diagram I posted, on a piece of paper and gave it to me telling me to hook them up that way.  It works.  It's hard to argue with success.

How many people here run their inverters at full max capacity at various times every single day, sometimes for up to two hours?  I'll bet few do.  But it's a good way to put the test to your battery bank and wiring to see if it can deliver the goods.
--
Chris

[Wolvenar]

Just for reference an image of half the bank back when it was new

[philb]

Seeing "GC2" on your batteries gives me more confidence in my GC2 Every Ready batteries. Does your batteries state who made them Wolv?

My first mini battery bank (T 105's) were running exclusively on wind power. They barely made it through 2 seasons before starting downhill. That could have been the two c-40's not charging them as well and not the T105's too.

I bought my first string of GC2's in February and the next set in March from Sam's. They stay balanced during absorb to within 0.2 volts even though they are in two separate strings. After they float, they are spot on with voltage and SG.

My Midnight Classic is setup on waste-not-hi and it is working beautifully. The little setup runs a fan, freezer and refrigerator plus charges the batteries on 3.1 kW per day. I know I will need more batteries when the other half and I move in, for sure.

I hope mine will run 9 years also.

[Wolvenar]

These started their lives on wind, but out of the 9 years at least 3 of it was used exclusively as backup power use so they sat in float voltages most of that time.  They had a rather hard life employed with wind. I had no charge control what so ever. I simply monitored voltages via the UPS that was acting as an inverter at that time.  The computer would turn on more loads or switch them to the offgrid power if the voltage were to stay above a certain point for a set amount of time, and start switching things back (via X10 control) if the voltage would drop below a point for so long etc.

They would still be doing a lot better if not for that wire corroding off and cooking some of the bank.
( inverters charger set to charge at a higher rate than the amount of batteries left should have been)
and the rest that were disconnected,  self discharged, then froze .

I am rather surprised how long they have lasted, it is certainly time for these to be joined by more, and possibly time for some to be retired.
But until that day we will just have to see how they hold up.

My worry is this winter when there are long nights and short cloudy days.

* Wolvenar makes a mental note. Prioritize that wind genny raise.

[ghurd]

* Wolvenar makes a mental note. Prioritize that wind genny raise.

That would be a good idea... even if it just a very small one to tinker with.
1)  Every little bit helps, especially in winter.
2)  2A / 60W is almost nothing in a bank that size, until it does it for 48 hours straight when the sun never showed up for those 2 days.
3)  More stuff like that, all of which you already know.

The original pair of Sam's 6V golf cart batteries are still in the string at the shop.
The string expanded over the years, but the hydometer still says they are fine (as of the last I knew, which was maybe 6 months ago).
A few years after the initial battery/solar install, added a pair of T-105s.
A few years later, added another pair of Sam's (pretty sure those are made by a 3rd company).
A few years later, added some used Sam's of the 3rd company variety, which were removed from a system being removed (long story that I don't have all the details about).
Sometimes during the winter, 12V 85 and 110AH class batteries are added.

The original pair must be 10 or 12 years old now.  They spent (typically) 7 months floating because there was no use for all the solar power, but they spend 2 months never reaching 13.0V, usually not even 12.3V weekly peak.

I'm just saying I am not all that opposed to adding new batteries in parallel with old, as long as the old still work properly.  I am sure the old pair has a lower than rated capacity, but they work.

Ghurd's mental note is this is half way through the 3rd summer, and the tower  progress is still 0.
G-