18 month check in (battery charging)

[Ajossy]

Howdy folks,

I have had my system installed in my motorhome for about a year and a half now and have had no issues, it's worked great, until last week.

The longest I had gone with out shore power was about 6 days (shortly after installing the system). Last week I went 8 days, and didn't quite make it.

Quick review of my system, 16x 271ah LiFeP04 batteries arranged in 2 banks of 8S2P to give me 24 volts and 542Ah. Victron Multiplus 24/3000/70 inverter, 1000W of solar fed via EPEver MPPT. My BMS are 200a Daly (came with the batteries), no Bluetooth or other means of monitoring the BMS. I do have a Victron 500A smart shunt that I use for my primary monitor.

On day 6 of my last off grid experience I had an inverter shut down. The shunt showed I was at 76% capacity. I started my generator and charged for a couple hours (it was nice to run the AC as well, was over 100 degrees where I was). Solar was spotty due to shade and weather, I was avoiding 110+ degree heat so mostly in the shade, but with clear skies was getting a good charge rates. However, thunderstorms arrived and cloud cover eliminated my solar window. I wasn't worried about it as I had plenty of battery left, or so I thought.

So here is the meat of my post, after getting home I started digging into my inverter settings and realized I was not fully charging my battery, I had absorption shutting off at 26.4 volts. Changed that to 29.2 and my inverter took all day to top off the batteries. This morning I checked cell voltages and things are not as balanced as I would expect.

Highest voltage in bank 1 is 3.596 and lowest is 3.339 Bank 2 is 3.545 a nd 3.342.
Do I need to re-balance my cells?
Should I replace my BMS with something I can monitor? I can only trust that they are working correctly. I am considering the Overkill Solar BMS.

Thanks in advance for all productive comments,
Andy

If case you are curious here are my cell voltages this morning:

Bank 1	Bank 2
3.341​	3.469​
3.339​	3.342​
3.454​	3.545​
3.493​	3.538​
3.509​	3.511​
3.519​	3.509​
3.508​	3.487​
3.596​	3.382​

 

[time2roll]

While some balancing is probably needed..... the inverter shutdown at 76% would seem something is falling off rapidly at the bottom. I would be interested in the low end voltages at the point of cut-off.

Since it has been 18 months to get out of balance, these cells might benefit from an active balancer. The OK BMS may not really provide a balance solution even if monitoring helps keep an eye on things. And then maybe the DALY has stopped balancing and the OK would do great.

I would tend to use a power supply to top up the low cells individually without disassembly. Looks like two cells in each battery need a significant boost.

 

[Ajossy]

Thank you for the prompt reply. I presume that the shut down was caused by the BMS not the inverter. I did check my cell voltages when it shut down but stupidly did not record them. oops.

I will dig out my power supply and see what I can do for Bank 1 cell 1 and 2, also bank 2 cell 2 and 8. Should I take the them to 3.65 or 3.5xx?

 

[time2roll]

Not much difference between 3.50 and 3.65 volts. Anything in that range is time to move to the next. Battery should be at and remain fully charged during this process. Might be fast enough for the cells near the top to do all of them.