Have I got a problem?

[Diddion]

I have a 40 panel solar array (10 kW). With a Solax x3 hybrid three phase controller. This was installed last year, and runs well. I have now (last week) installed four 2.4 kWh batteries. According to the software the maximum charge is 98%, whether charged from the grid or from the panels. They discharge to 20%, which I know is right.

Is this what I should expect from new batteries, or do I have a problem with the batteries, the system, or the system adjustment? It has occurred to me that it could be a deliberate setting (perhaps to extend battery life?). Your assessments will be much appreciated

[Ampster]

I have a 40 panel solar array (10 kW). With a Solax x3 hybrid three phase controller. This was installed last year, and runs well. I have now (last week) installed four 2.4 kWh batteries. According to the software the maximum charge is 98%, whether charged from the grid or from the panels. They discharge to 20%, which I know is right.

Is this what I should expect from new batteries, or do I have a problem with the batteries, the system, or the system adjustment? It has occurred to me that it could be a deliberate setting (perhaps to extend battery life?). Your assessments will be much appreciated

Tell us some more about the batteries and the type of chemistry? Different types take different charges. It sounds like that charge/discharge range is Lithium and that would appear to be a conservative setting to extend battery life. With Lithium batteries there is not that much more capacity between 98% and 100% so you are not missing much.
Is the software in the inverter or related to the batteries?

[Diddion]

Thanks, Ampster. Some info. for you (And I hope it means more to you than to me!). I am not concerned at a 2% reduction in maximum charge as such, especially if it extends battery life, but I would be concerned if it meant something was wrong!

There is a stack of four Pylontech batteries, each bearing the code H48050. https://zerohomebills.com/product/py...attery-module/
The housing also contains a Pylontech SC0500 Controller. This bears a sticker stating 100A max, 430Vdc. Judging by the warnings on it, this is a pretty dangerous piece of kit - not that I would ever dream of even opening the cabinet.

The inverter is a Solax X3 Hybrid, 10kW three phase. There might be another issue, here, but it could also be associated with the above. When taking the battery details I decided to alter the forced charging time (to charge the batteries from the grid during a low tariff period). However, when I tried to access the menu I received the message DSP-COMM FAILURE, and could go no further. Bit puzzled (No...... very puzzled).

[Mike90250]

I'd get tech support from the vendor/installer/dealer. Mess those settings up and it could cook your batteries. Li batteries should only be cycled low 20%, high 90% or you can greatly shorten their life, with even brief over or under charge - no forgiveness !!

[Diddion]

Thanks, Mike. Interestingly, the battery specs show 80% DOD, going from 10 to 90%. Do you feel that to be a sensible range, from a longevity point of view (as opposed, for example, to 15-90, though this would somewhat eat into the usable capacity). I have emailed the installer, asking for him to deal with this, and to find out what that error message was all about.

[Ampster]

The big question is whether the SOC meter is based on usable capacity (2000Watts) or actual capacity (2400Watts). From reading the link, the good news is it is LFP chemistry which is one of the safest Lithium chemistries. They say the nominal voltage of the pack is 48 volts which most likely means 16 LFP cells in series. They also say the voltage range of the pack is 45 to 54 volts. That equates to a cell voltage of 2.8 volts to 3.375 which is a conservative maximum voltage for that chemistry.

[Diddion]

The big question is whether the SOC meter is based on usable capacity (2000Watts) or actual capacity (2400Watts). From reading the link, the good news is it is LFP chemistry which is one of the safest Lithium chemistries. They say the nominal voltage of the pack is 48 volts which most likely means 16 LFP cells in series. They also say the voltage range of the pack is 45 to 54 volts. That equates to a cell voltage of 2.8 volts to 3.375 which is a conservative maximum voltage for that chemistry.

If the SOC meter were based upon usable capacity, would it not give a range of 0 to 100%? Since the minimum capacity shown is 20%, the inference must be that the SOC is reading actual capacity. Are you saying that the cell voltage should be ok if it is set to charge to 98%. In other words, having looked at the specs, would you disagree with Mike (above), suggesting a lower maximum percentage?

I also wonder if there is any significance or impact of my system being 20 to (near) 100, with the specs giving 10 to 90.%.

[Ampster]

If the SOC meter were based upon usable capacity, would it not give a range of 0 to 100%? Since the minimum capacity shown is 20%, the inference must be that the SOC is reading actual capacity. Are you saying that the cell voltage should be ok if it is set to charge to 98%. In other words, having looked at the specs, would you disagree with Mike (above), suggesting a lower maximum percentage?

I also wonder if there is any significance or impact of my system being 20 to (near) 100, with the specs giving 10 to 90.%.

I am not disagreeing with Mike. I am saying that it is common among EV manufactures to have hidden capacity so that when your meter reads 100% you are actually at 90%. The same may be true with packaged batteries like these, especially if they guarantee 8,000 cycles. As I said earlier, their literature says that the actual capacity is 2400 and usable capacity is 2000, which equates to 80%. I made those calculations to come up with the assumptions about the safe max voltage which on a LFP charge curve would be about 90% of capacity when charged to 3.4 volts per cell or a pack voltage of 54 volts.

The best advice I can give is to follow the manufacturers recommendations in order to preserve the guarantee.

[Mike90250]

I'm not a user of Li batteries, but I know many of their pitfalls. never 0-100% 10-90% might be OK, 20-90% is ok too. The low end is where the danger is, depending if all the cells in the pack are well matched going to 10% is OK. If they were not well matched, 20% is better, taking a cell to 0 is fatal from what I understand. At the mid point, battery voltage does not change much, but at the extremes, the last couple % happen very quickly, so depending on the measuring equipment design, calibration, setup and aging, you don't want to get into the dangerous territory.