Batteries in 2x2 series-parallel config with weird discharge???

[Bowlegs868]

Hi

New guy here.

I seem to be having battery problems. I started with 6 batteries at first now I'm down now a new set of 4.

A couple days ago, my charge controller screen started behaving erratic... voltage readings were bouncing all over, warnings popping up on screen etc. After checking them with my multimeter, 2 of the 4 batteries (one from each series) were way lower than the other two. I don't think they were installed with different voltage levels because the installer took them home to charge/balance all four batteries.

I've also had the same problem with the previous set of batteries.

Could anyone give me some answers as to what can be the cause for this? Why one battery in the series drops so low if they started out at the same level?

Charge controller: Epever VS6048AU
Battery: Eaton PWHR12390W4FR (wired in series-parallel)
Inverter: Kayal KYNB-C2000-124CD

 

[rmaddy]

Show a clear picture of how your SLA batteries are all wired up to you system.

 

[Bowlegs868]

sorry about that... I had to rewire the two "good" batteries for my system to work but that's what it looked like before

 

[rmaddy]

It would be better to see an actual photo of the actual wiring but at a minimum you need to move the left of the two blue wires in your diagram so it is connected to the negative terminal of the right-most battery instead of the negative terminal of the 2nd battery.

I don't have any experience with SLA batteries, just LiFePO₄, so I don't know if there is the same requirement. But when putting batteries in series you must make sure that they are at the exact same state of charge (SOC) before connecting the two in series. Assuming this also applies to SLA batteries I suggest the following steps. Fully charge each battery individually. Then put two batteries in parallel. Connect the positive lead of the charger to the positive terminal of one battery and the negative lead of the charger to the negative terminal of the other battery. Fully charge the two batteries together in parallel. When done, leave the two batteries connected in parallel for a few hours. Repeat with the other two batteries. When done, reconnect the first pair in series. Reconnect the second pair in series. Connect those two series strings in parallel with the change I mentioned above. Now you should have a properly balanced 2S2P battery bank.

 

[740GLE]

Pictures of wiring and connections would help a ton.

What’s the typical loads served? What gauge wiring?

 

[12VoltInstalls]

voltage readings were bouncing all over, warnings popping up on screen etc.

What voltages?
What warnings?
What sun conditions?
What charging mode?
What’s your low voltage limit in volts?

What electrolyte level?

(i Agree your cables could be better)

 

[Bowlegs868]

It would be better to see an actual photo of the actual wiring but at a minimum you need to move the left of the two blue wires in your diagram so it is connected to the negative terminal of the right-most battery instead of the negative terminal of the 2nd battery.

I don't have any experience with SLA batteries, just LiFePO₄, so I don't know if there is the same requirement. But when putting batteries in series you must make sure that they are at the exact same state of charge (SOC) before connecting the two in series. Assuming this also applies to SLA batteries I suggest the following steps. Fully charge each battery individually. Then put two batteries in parallel. Connect the positive lead of the charger to the positive terminal of one battery and the negative lead of the charger to the negative terminal of the other battery. Fully charge the two batteries together in parallel. When done, leave the two batteries connected in parallel for a few hours. Repeat with the other two batteries. When done, reconnect the first pair in series. Reconnect the second pair in series. Connect those two series strings in parallel with the change I mentioned above. Now you should have a properly balanced 2S2P battery bank.

Wow... this is not for the faint of heart! ? Haven't been able to rest 6 months straight without something going wrong with my system and I really can't afford having to replace components for much longer.

At least forums like these exist so you don't make the same mistakes again.

Thanks, rmaddy

 

[noenegdod]

View attachment 83040
sorry about that... I had to rewire the two "good" batteries for my system to work but that's what it looked like before

I didnt see this anywhere in any other replies but the battery on the left will be drawn down preferentially first because of how you wired them. The main ground wire should be attached to the extreme right negative post.

 

[Bowlegs868]

Pictures of wiring and connections would help a ton.

What’s the typical loads served? What gauge wiring?

5 cu ft. fridge, 5 LED lights, 70W fan, 40-inch TV, WiFi router, 560W washer... those are the everyday/weekly items.

6 AWG on mains, and I'm guessing 8 AWG on batteries. I'm not the system builder so I don't have all the finer details... but I'm learning more about it each time something breaks down...

The picture below only shows the two batteries I have connected because the other two is sitting at 11.6 and 11.1

 

[Bowlegs868]

I didnt see this anywhere in any other replies but the battery on the left will be drawn down preferentially first because of how you wired them. The main ground wire should be attached to the extreme right negative post.

Thanks, noenegdod
I found that out last night after perusing the forum. Looks like I'll be buying MORE batteries again soon

 

[Bowlegs868]

What voltages?
What warnings?
What sun conditions?
What charging mode?
What’s your low voltage limit in volts?

What electrolyte level?

(i Agree your cables could be better)

from left to right (batteries):
11.6
11.1
14.9
13.8

as for the warnings, the charge controller was showing a flashing empty battery with a flashing warning symbol, then it will suddenly jump to a full battery, or sometimes two bars and it will do this over and over especially when power is coming in from the panels

this was happening when the two lower batteries were connected.

I live in the Caribbean so sun isn't a problem... I can't answer for the other stuff but I'm using an Epever VS6048AU charge controller

 

[Smokin]

Theroreticly and in pratice, Lead Acid batteries suck.
Lead acid seem to go short on life span when you need them most. That's why the shift to Lifepo4.
Those low batteries should be slow charged and checked to see where they are at.

Oh your down island where the butter melts.

 

[12VoltInstalls]

5 cu ft. fridge, 5 LED lights, 70W fan, 40-inch TV, WiFi router, 560W washer... those are the everyday/weekly-items.

How deeply are you discharging?
Below 12.1 volts is not good

6 AWG on mains, and I'm guessing 8 AWG on batteries.

8ga between batteries is too small. That will amplify the problem you experienced
6ga to inverter? That’s too small

The picture below only shows the two batteries I have connected because the other two is sitting at 11.6 and 11.1

full charge each battery
They may recover.

Looks like I'll be buying MORE batteries again soon

Again, fully charge and balance- they may recover.

Haven't been able to rest 6 months straight without something going wrong with my system and I really can't afford having to replace components for much longer.

If it were me I’d have at least 1ga between batteries and 2/0ga to the inverter. Not 2ga, 00 aka 2/0. That’s oversize but is going to eliminate cabling concerns. Not required- what I do and have done on my own 800W setup.

After that I’m guessing 8 total batteries will be just enough except for winter maybe.

How many panels and what watts?
And what region are you?

What’s your low voltage limit in volts?

you need to configure to never go below 12.1V each, 12.3 is better.

Theroreticly and in pratice, Lead Acid batteries suck

This is not always true.
Lead may not always be a logical choice- but for many including myself they do not suck and work quite well, and can be inexpensive over time in many installations.

I think flooded lead acid is a better battery than sealed for daily cycling and I would be inclined to plan for that route. Then plan your next upgrade to decide if LiFePo batteries make sense for you. They can be less money over a 15-year aging. Lead batteries have worked well for me but LiFePo can be a better choice. Eventually they will probably become the best choice almost always.
Cost-wise cheap walmartha marine batteries have worked out quite inexpensively for me but that is my circumstances. YMMV

 

[Bowlegs868]

Theroreticly and in pratice, Lead Acid batteries suck.
Lead acid seem to go short on life span when you need them most. That's why the shift to Lifepo4.
Those low batteries should be slow charged and checked to see where they are at.

Oh your down island where the butter melts.

Thanks a lot for that tip! I think I'm ready to put these lead acid batteries far behind me and make the switch.

@melting butter... ha! indeed ?

 

[Bowlegs868]

How deeply are you discharging?

I would say it's been down to around 24.4V as a bank

How many panels and what watts?
And what region are you?

4 panels at 350W each
I live in the Caribbean (Trinidad and Tobago)

full charge each battery
They may recover.

I'm hoping and praying that they do!

thank you for sharing your knowledge!! ?