Lithium Cell Balancing at Nowty Towers - Resurrections

[nowty]

I have a spreadsheet which blends the 3 strings of mixed battery chemistry together and gives me this quick ready reckoner for the capacity and status of my home battery verses the battery voltage reading.

[openspaceman]

similarly I have been trying to compare my battery indicated SOC with voltage in the order I randomly checked yesterday-today:

38% 53.1V
60% 53.8V
99% 53.1V
86% 53V
50% 51.8V
49% 52.5V
20% 52.1V
78% 54.5V
93% 53.1V

Now I assume the charger is limited to 54.5V and the variance is to do with the internal resistance of the battery meaning the voltage goes higher when charging and lower when discharging and the charger also integrates Amps in and out to give a SOC %?

Also given Joeboy's advice, to limit the voltage of my MPPT charger for my new panels to a couple of points below my growatt ac coupled charger, I should set it no higher than 54.3V?

Some way off yet as electrician still hasn't found time for a site visit.

[nowty]

My voltages are based on zero charge or discharge but my battery bank is so large that it does not vary too much with high charge/discharge rates and my remote voltage monitor is clipped onto the Battery itself so it’s not measuring any voltage drops in the cables from the battery inverter.

[Joeboy]

My voltages are based on zero charge or discharge but my battery bank is so large that it does not vary too much with high charge/discharge rates and my remote voltage monitor is clipped onto the Battery itself so it’s not measuring any voltage drops in the cables from the battery inverter.

That is excellent Nowty, I will be adding something to the extended stack and seeing your xl sheet helped my mind go click.

[nowty]

Full burn in test today of the new cell protectors, it just about hit the protector limit yesterday with one protector board switching on for only a few seconds but the sun was waning. Today its full sun and I watched as one by one they came on, first flashing then on full with that lovely new circuit board burning smell.

The voltage on the new cell hit 3.66V max and then as the Pylontechs throttled back as they hit their cell ceiling voltage at around 3.52V, the lights went out one by one, they were only on for a few minutes. The voltage on the new cell is now 3.60V with one board still flashing. All Pylontechs have now gone into standby and my Growatt strings are also topping out.

[Joeboy]

Full burn in test today of the new cell protectors, it just about hit the protector limit yesterday with one protector board switching on for only a few seconds but the sun was waning. Today its full sun and I watched as one by one they came on, first flashing then on full with that lovely new circuit board burning smell.

The voltage on the new cell hit 3.66V max and then as the Pylontechs throttled back as they hit their cell ceiling voltage at around 3.52V, the lights went out one by one, they were only on for a few minutes. The voltage on the new cell is now 3.60V with one board still flashing. All Pylontechs have now gone into standby and my Growatt strings are also topping out.

Cracking build, very neat.

[nowty]

Well there was an empty space, where a final 9th Pylontech could fit.


Now, just because there is a space does not mean it needs filling, or maybe it does. It did make sense to add a final one to get a bit more out of the extra cell I added earlier, so this 2.4kWh battery effectively acts like a 2.56kWh battery because it unlocks an extra part of the extra 16th cell. You don't understand ?, you will have to recap a few pages.

Also my bank gave me a 0% credit card for 23 months, so one last wafer thin battery could be paid for with the 2024 FIT payments. Last, this and next years FIT payments are already taken up with the Ripple windfarms. Given the rate of inflation, which is expected to be around for the next 3 years, might also be worth doing it now, rather than later.

It arrived today from itstechnologies and my QA manager first checked it over.



Hmmmmmm, pussy pointed out that although it was a US2000C Pylontech, it was a re-badged import from Spain.



I updated my battery spreadsheet and it now says my gross battery size is 72 kWh and the useable size is 60 kWh.

Now in operational service. , but I need the help of some heavy pain killers.

[Joeboy]

Congratulations Nowty, a great read. My favourite and very recognisable was the batch of multi rationale in the middle! All kidding aside, the fact that your FIT's can cover the cost of something as solid as a Pylontech battery is excellent, more power to ye!

[nowty]

I had to purchase two of the new US2000C's to add the 9th battery as I had to also replace the Master battery with a US2000C as well as for the new 9th battery.

I sold on the 5 year old sulplus Pylontech battery on Ebay last night at what I paid for it 5 years ago and within a couple of hours of listing. I took advantage of an Ebay selling offer and only paid £1 commission.

Battery wise I am now done for the foreseeable future.

I did a couple of little tweaks to my blended battery capacity spreadsheet.

[nowty]

I think I must have broke my battery bank discharge record yesterday at nearly 46 kWh. My Pylontech bank had shutdown but the Growatt banks were still throwing out the amps with about another 10 kWh remaining according to my cheatsheet.