Off-Grid Solar Charging Issue – Low Charging Power When No Load

[ogikhan]

Hello everyone,

I have an off-grid solar system with the following setup:

5kVA inverter
6 x 380W solar panels (connected in series-parallel)
JK BMS B2A24S20P
16s LiFePO4 280Ah battery (EVE LF280K)
Completely off-grid system
Issue:
When I check the solar input, my panels produce 90V under normal conditions. The problem is with how my inverter is handling charging:

When a high-power load (e.g., an electric kettle) is turned ON, the solar panels output 2.2kW of power.
The inverter provides 1kW to my house, and the remaining 1.2kW goes to charging the battery.
When no load is present, the inverter only charges the battery at 380W, even though more solar power is available.

What I Have Done So Far:
Changed Inverter Settings:
Charge Priority: Solar First
Output Source Priority: SBU Mode
Bulk Charge Voltage: 57.6V
Float Charge Voltage: 54.0V
Updated JK BMS Settings:
Max Charge Current: 150A
Start Balance Voltage: 3.45V
Checked Solar Input Voltage: Confirmed around 90V

 

[wme]

Do you have a shunt to measure SOC of your batteries. You cant do much charging on a full battery

 

[ogikhan]

Do you have a shunt to measure SOC of your batteries. You cant do much charging on a full battery

Thank you for your response.
According to my JK BMS dashboard:
Voltage: 52.54V
Remaining Battery: 31% SOC

 

[Drizzt321]

What are your cell voltages? Unbalanced cells with one or more being higher than the rest might lead to premature "slowdown" of charging, so to speak.

 

[rhino]

Also with a voltmeter check the voltage of the batteries right where they connect to the inverter so you know exactly what voltage the inverter is seeing.

 

[rhino]

You can also calibrate the voltage by measuring what the voltage is directly on the most positive and most negative terminal of the battery and compare that to what the JK BMS shows. There is setting to then change it to what you measure in the JK BMS app in case it doesn't match. Mine have been off by a bit in the past when I build one.

 

[ogikhan]

What are your cell voltages? Unbalanced cells with one or more being higher than the rest might lead to premature "slowdown" of charging, so to speak.

Jk bms settings everything balanced

 

[ogikhan]

You can also calibrate the voltage by measuring what the voltage is directly on the most positive and most negative terminal of the battery and compare that to what the JK BMS shows. There is setting to then change it to what you measure in the JK BMS app in case it doesn't match. Mine have been off by a bit in the past when I build one.

i already did this

 

[Drizzt321]

Jk bms settings everything balanced

Can't hurt to also check the cells manually, if possible, to validate that it's reading them right. Probably is.

Does the inverter/MPPT have a shunt? Is it, instead of measuring voltages, measuring current in/out? You might need to tell it to think the charge is currently lower than it thinks it is, and reset/calibrate 100% when the BMS shows it's 100%.

Also as suggested, check that the voltage at the inverter/MPPT on the battery side, that it roughly lines up with the BMS. Though sounds like you have.

What model of inverter/MPPT do you have?

 

[ogikhan]

Can't hurt to also check the cells manually, if possible, to validate that it's reading them right. Probably is.

Does the inverter/MPPT have a shunt? Is it, instead of measuring voltages, measuring current in/out? You might need to tell it to think the charge is currently lower than it thinks it is, and reset/calibrate 100% when the BMS shows it's 100%.

Also as suggested, check that the voltage at the inverter/MPPT on the battery side, that it roughly lines up with the BMS. Though sounds like you have.

What model of inverter/MPPT do you have?

inverter is this one pdf https://d2v0huudrf11kh.cloudfront.net/vevor-center-goods/MPS-40A-60A_1677721677162.pdf
inverter settings:

02: 100
05: USE
26: 57.6V
27: 54.0V
29: 48.0V
I have ordered a True RMS clamp ammeter and I am waiting for it to arrive. I am trying to measure with a low-quality Chinese voltmeter for now.

The inverter battery voltage and BMS voltage are different; there is a 0.5V difference.bms 52.10 inverter 52.05

 

[HarryN]

Just throwing out ideas - do you have a clamp meter to measure current ?

 

[ogikhan]

Just throwing out ideas - do you have a clamp meter to measure current ?

I Thave ordered a True RMS clamp ammeter and I am waiting for it to arrive.Uni-t UT204+

 

[Drizzt321]

What's setting #13? Make sure that's set to 54v, I think would be the right value. If I'm understanding the manual correctly.

 

[TM48]

The manual you linked to says to only use a lead acid or AGM battery.

 

[ogikhan]

The manual you linked to says to only use a lead acid or AGM battery.

Battery user-defined mode

 

[ogikhan]

What's setting #13? Make sure that's set to 54v, I think would be the right value. If I'm understanding the manual correctly.

I currently don't have access to the inverter, I think that setting is used in on-grid systems, but my system is completely off-grid