Help de bunking vendors “FUD”

[OldCodger]

So while trying to understand my system I asked my vendor why my system wasn’t charging /discharging at its rated capacity

System Growatt SPH3000 inverter. 3.3kWh Ml33RTA battery

Inverter should discharge at 3kW. Batteries should charge at the same rate from the grid.

But they don’t.

The battery only seems to charge at 2.16 kW.

When I queried this my vendor said the batteries can only charge at full rate when between 20 and 40c .

They are LiFePO (LFP?) batteries

Is this real or just designed to confuse me?

Is there really a temp limit in charging/discharging?

I know there’s a lower limit of don’t charge below 0c but 20c to restrict charge rate?

My batteries are in an unheated space (attic) it’s 10-15c this time of year, but I’d guess the “self heating” of the batteries would put it above the surroundings?

Can anyone help?

 

[Mattb4]

Depends on the maximum charge rate your setup allows from grid. Should be available from your manual. The output from the inverter does not have to equal charging amount and if it did there would be none left to pass through to other loads.

ETA: BTW, yes the vendors account was total hogwash.

 

[DIYrich]

Charging may slow above 80% soc.

 

[OldCodger]

Charging may slow above 80% soc.

This was happening at 65% recently - this is a typical screen shot charging from the grid during a low cost period to reduce cost of electricity in a peak cost period.




And on another day, while dischargIng





I can’t find any settings that limit the charger or inverter rates. Are there any?

 

[OldCodger]

ETA: BTW, yes the vendors account was total hogwash.

Thank you.

Depends on the maximum charge rate your setup allows from grid. Should be available from your manual.

I’ll have another look, I was told it a 3kW charger. As I’ve decided to add another 3.3kWh of batteries I’d rather fix this “problem” than double my charger time, or, more importantly, be “forced” to import power from the grid when prices are high just because the inverter is in some way artificially limited.

 

[OldCodger]

Data sheet suggests I should get 3kW out of the inverter

https://www.ginverter.com/upload/file/SPH_3000-6000TL_BL-UP_Datasheet_202303.pdf

If I am reading it correctly so does the full manual

https://www.ginverter.com/upload/file/SPH_3-6KTL_BL-UP_User_Manual_EN_202401.pdf

(Page 62?)

 

[DIYrich]

The closest I could see on battery parameters are:
Page 45, section 1. Seems like only lead acid give amp option.
Page 46: power rate - is it 100%?

 

[Mattb4]

Data sheet suggests I should get 3kW out of the inverter

https://www.ginverter.com/upload/file/SPH_3000-6000TL_BL-UP_Datasheet_202303.pdf

If I am reading it correctly so does the full manual

https://www.ginverter.com/upload/file/SPH_3-6KTL_BL-UP_User_Manual_EN_202401.pdf

(Page 62?)

The manual states 85 amp max DC charging. 85a X24vDC =2040w Thus your 2160w is just about what you would expect at actual battery voltage.

 

[OldCodger]

The manual states 85 amp max DC charging. 85a X24vDC =2040w Thus your 2160w is just about what you would expect at actual battery voltage.

Thanks. Are you saying I should see about 2040 charge rate into the battery? I only see 1740 see the first screen shot?

I thought the batteries were at 50v ? Or am I about to learn something more about PV ?

 

[Mattb4]

Thanks. Are you saying I should see about 2040 charge rate into the battery? I only see 1740 see the first screen shot?

I thought the batteries were at 50v ? Or am I about to learn something more about PV ?

Sorry my error. I thought you had one of the 24vDC units. Reading through the manual I do not see any place that DC amperage can be adjusted. Just the max. Your unit is a bit complex being a grid interactive unit.

 

[OldCodger]

Sorry my error. I thought you had one of the 24vDC units. Reading through the manual I do not see any place that DC amperage can be adjusted. Just the max. Your unit is a bit complex being a grid interactive unit.

Ok. Thank you.

 

[400bird]

I'd recommend checking the battery spec sheet. My quick Google search looks like you are running into a limit of the battery.
50 volts x 40 amps = 2000 watts, so if these numbers are correct that make sense.

 

[OldCodger]

I'd recommend checking the battery spec sheet. My quick Google search looks like you are running into a limit of the battery.
50 volts x 40 amps = 2000 watts, so if these numbers are correct that make sense.

View attachment 194885

Thanks. I’d started down that road! This confirms it.

Out of interest would putting a second battery in parallel allow me to double the charge rate?

 

[400bird]

Thanks. I’d started down that road! This confirms it.

Out of interest would putting a second battery in parallel allow me to double the charge rate?

Basically yes, but there's a couple caveats.
1. I might have found the wrong spec sheet.
2. It would double how much energy the batteries can accept (not how much the inverter can put out).
3. If using battery comms, it must be able to figure out there are two batteries and update/communicate the new limit to the inverter.

 

[OldCodger]

Basically yes, but there's a couple caveats.
1. I might have found the wrong spec sheet.
2. It would double how much energy the batteries can accept (not how much the inverter can put out).
3. If using battery comms, it must be able to figure out there are two batteries and update/communicate the new limit to the inverter.

That’s good news!

And that’s the right spec sheet. The guy selling me the batteries sent it to me

Elsewhere I’ve seen that the system “auto configures” the battery capacity- there’s a daisy chain cat 5 cable that I need to plug in.

I’ll let you know!

 

[OldCodger]

Just to close this out should anyone else ask, yes it was the battery spec that was limiting charge and discharge rates.

Adding another battery in parallel will allow up to double the charge and discharge rates - so it will be the inverter 3kW that limits things. Which is what I want.

 

[Steve_S]

Far to many vendors (resellers) play with numbers thinking they are making their "stuff" seem better than it is... One TRUTH exists in all of this, is the Chemistry Itself has it's design specs, limits and restrictions. This applies to every single battery chemistry and each is unique. Many "Battery" repackers do the STOOPID and IGNORE the chemistry limits and choose to make people push the batteries over design spec.

LFP like every other chemistry out there has TWO Voltage Ranges...
The Allowable range where the voltages cause NO HARM to the cells. For LFP that is from 2.500 to 3.650 Volts per cell. This is the Safe Voltage Range !
The Working Range is the Voltage Range that actually delivers the specified AmpHours of the cells. This is that Flat Voltage Curve and it runs from 3.000-3.400 Volts per cell.

Pushing cells above 3.450 does nothing other than stress the cells. Running cells below 2.800 is also causing stress with NO POSITIVE RETURN !

Battery Packs in Parallel Divide & Share both Load & Charge.

A Respectable moderate charge profile keeps all cells within the working voltage range and maximizes the lifecycles & energy capacity over time.

Good Moderate Charge Profile:
ll equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT)
Divide Values X2 for 12V. Multiply X2 for 48V.
Bulk / Absorb: 27.6V (Absorb for 45 minutes (3.45vpc) (some call this boost)
Equalize: OFF
Float 27.5V (3.437vpc)
MIn Volts: 21.2V (2.650vpc)
Max Volts: 28.6V (3.575vpc)
Rebulk Voltage: 25.6 (3.200vpc)
End Amps/TailCurrent: *1 (Triggers change from Absorb to Float)
(*1): End Amps is calculated: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current Constant Voltage) and then float (Constant Voltage, Variable Current) tops off so the cells are at 3.437Vpc. I
! Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.

BMS With Active Balancing should be set to start Active Balancing at 3.420V or possibly lower to 3.410 so that the cells can balance out at the top and not affect the charging process.

Very Special NOTE: Floating & Saturating to 3.437vpc, accounts for the Voltage Settling post Charge of any kind which actually brings the cells to just below 3.400Vpc.

A NOTE ON CHARGER !
Assuming that the Growatt can actually do 3000W, 3000W ÷ 51.2V = 58.6A MAX charge capacity and appears to be safety derated to 45A which is not unusual... 45A X 51.2V = 2304W.

QUICK REF TO KEEP HANDY

 

[OldCodger]

Far to many vendors (resellers) play with numbers thinking they are making their "stuff" seem better than it is... One TRUTH exists in all of this, is the Chemistry Itself has it's design specs, limits and restrictions. This applies to every single battery chemistry and each is unique. Many "Battery" repackers do the STOOPID and IGNORE the chemistry limits and choose to make people push the batteries over design spec.

LFP like every other chemistry out there has TWO Voltage Ranges...
The Allowable range where the voltages cause NO HARM to the cells. For LFP that is from 2.500 to 3.650 Volts per cell. This is the Safe Voltage Range !
The Working Range is the Voltage Range that actually delivers the specified AmpHours of the cells. This is that Flat Voltage Curve and it runs from 3.000-3.400 Volts per cell.

Pushing cells above 3.450 does nothing other than stress the cells. Running cells below 2.800 is also causing stress with NO POSITIVE RETURN !

Battery Packs in Parallel Divide & Share both Load & Charge.

A Respectable moderate charge profile keeps all cells within the working voltage range and maximizes the lifecycles & energy capacity over time.

Good Moderate Charge Profile:
ll equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT)
Divide Values X2 for 12V. Multiply X2 for 48V.
Bulk / Absorb: 27.6V (Absorb for 45 minutes (3.45vpc) (some call this boost)
Equalize: OFF
Float 27.5V (3.437vpc)
MIn Volts: 21.2V (2.650vpc)
Max Volts: 28.6V (3.575vpc)
Rebulk Voltage: 25.6 (3.200vpc)
End Amps/TailCurrent: *1 (Triggers change from Absorb to Float)
(*1): End Amps is calculated: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current Constant Voltage) and then float (Constant Voltage, Variable Current) tops off so the cells are at 3.437Vpc. I
! Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.

BMS With Active Balancing should be set to start Active Balancing at 3.420V or possibly lower to 3.410 so that the cells can balance out at the top and not affect the charging process.

Very Special NOTE: Floating & Saturating to 3.437vpc, accounts for the Voltage Settling post Charge of any kind which actually brings the cells to just below 3.400Vpc.

A NOTE ON CHARGER !
Assuming that the Growatt can actually do 3000W, 3000W ÷ 51.2V = 58.6A MAX charge capacity and appears to be safety derated to 45A which is not unusual... 45A X 51.2V = 2304W.

QUICK REF TO KEEP HANDY

Thanks, I’ve read that a couple of times and even though I’m a retired chemical engineer much of it doesn’t immediately make sense. (I don’t comprehend, rather than I think it is nonsense.)

However, as I explained I know it is the battery charging/discharging limits that define my problem. Fitting a second battery will “fix” my problem as it will be my inverters limits that define my constraints , not my battery.