I didn't top balance my packs before installing

[Andy]

They will only balance at the higher voltages due to the charge voltage curve of the batteries.

Remember to lower the voltage back down again after you have balanced them.

It is strange because I was floating for 5-6 hours a day in the summer so I was really expecting it to be done by now. How long did it take you?

[Andy]

For example here is a day in Jul.

[Tinbum]

They don't actually balance most of the time because they are well balanced during most of the curve.

You will never see the imbalance at normal voltages only at high cell voltages and low cell voltages. Have a look at Nowty's cell voltage SOC chart below.

[Andy]

I think I've worked out why. I just look at the graphs and I didn't put the last three banks in until the end of Aug. Since then, it operated largely up to 80%. It rarely tipped 100% for more than a few minutes due to my predictive charging. I just need to give it more time as you say.

[Andy]

They don't actually balance most of the time because they are well balanced during most of the curve.

You will never see the imbalance at normal voltages only at high cell voltages and low cell voltages. Have a look at Nowty's cell voltage SOC chart below.

That's why I'm confused by that split about half way down. It's showing when I use my multimeter as well.

[Tinbum]

For example here is a day in Jul.

The voltage is reducing before the batteries have balanced.

[Andy]

For example here is a day in Jul.

The voltage is reducing before the batteries have balanced.

Is it not a cumulative process? 5hrs balancing a day is the same as a continuous balance? Or does a discharge undo all the work from before?

[Tinbum]

They don't actually balance most of the time because they are well balanced during most of the curve.

You will never see the imbalance at normal voltages only at high cell voltages and low cell voltages. Have a look at Nowty's cell voltage SOC chart below.

That's why I'm confused by that split about half way down. It's showing when I use my multimeter as well.

Between 50% and 85% SOC their is only 0.03v difference, that's nothing for such a difference in SOC.

Your battery cells are just badly balanced- give them a good long balance and they will come back ok.

From your graph they don't seem to be getting much of a balance each day- the voltage is going down too early.

[Kommando]

What Tinbum says is correct.

This is my experience.

If you have an inverter that reacts to a BMS report of 100% SOC by switching off charging then move to 15.35. This will not use the inaccurate BMS shunt to prematurely report 100% SOC but instead will stick at 99% until the RCV V is reached so the inverter will do more balancing.

I use a pair of SMA SI's which ignore 100% SOC from the BMS and only limit charging when the Target RCV V is reached which I have set at 55.2V. It then cutails the PV output and maintains 55.2V during which time the cells balance.

For both batteries I never top balanced the cells before connecting to the SI's, I set the balance V to 3.4V and let the JK PB do its thing and then once a good cell delta.was reached I set the balance to 3.449V Battery 1 took 1 day to fully balance with a final delta of 0.005V down from 0.080V as there was plenty of sun. Bat 2 took 3 weeks but only because the sun disappeared, the balancing was done over 2 days 3 weeks apart. Bat 2 initial delta at 3.4V was 0.120V and so I intervened and using a lab power supply took the two low cells up individually whilst they were still connected in the battery pack. The single high runner cell I left the JK to sort out which it did.

Once the 2 bats were balanced then once 3.449V is reached it takes 20 mins to get the delta V back from typically 0.012V to 0.008V. Even with a gap of 3 weeks between reaching 3.449V it only takes 40 mins.

[Andy]

Well, I've been charging as fast as possible to give more time at the top each day for balancing. It definitely seems to be getting on top of things finally.

Here is a chart of the difference between top cell and bottom cell in the pack. The trend is in the right direction. Thanks for all assistance.