Fox KH10 AC Coupled Battery Charging/Discharging Issue

[Safiq]

Hi all,

I have a recently installed a Fox ESS KH10 single-phase hybrid inverter with around 42kWh battery in an AC-coupled setup. The existing solar system is connected to a Sungrow AC inverter.

I’m having issues with battery charging/discharging behaviour and wanted to see if anyone has experienced something similar or has ideas on what could be wrong.

Expected behaviour should be:

• Battery charges when there is excess solar generation
  Battery discharges when house load is higher than solar generation

However, what is happening is:

The battery continues discharging even when there is excess solar available
Battery discharges down to 10% SOC and then stops
The only way I can get the battery to charge is by increasing the minimum SOC to something like 50%
When I do that, the battery may be charging using both solar and grid power, instead of only using excess solar energy

System setup:

• Fox KH10 hybrid inverter
  Approx. 42kWh battery
  Existing AC Sungrow 8KW inverter + 10KW Jinko Panels
  Two CT clamps installed
  Distance between inverter and meter box is around 10–12 metres

CT setup:

• One CT is clamped on the AC cable coming from the Sungrow inverter, with the arrow pointing toward the meter box
  The second CT is clamped on the grid live wire, with the arrow pointing toward the grid

The installer has confirmed that the setup matches Fox’s recommended AC-coupled configuration.

Has anyone experienced similar behaviour in an AC-coupled Fox setup?

Unfortunately, the installer has been extremely busy through April and I’ve been waiting several weeks for a follow-up visit. He is finally coming back next week to “take a look,” but I wanted to check with the community first in case there are common issues in AC coupled setup.

Any advice would be greatly appreciated.

[Dave Foster]

It sounds as if one (or both) of your CT’s are not being read correctly.

CT1 should be connected to the live feed of your supply meter and it measures the amount of power flowing in and out of the house, the battery then attempts to balance this to zero which is your house load.

If you have seperate solar panels, the inverter doesn’t know what the generation is and so it will get house load wrong, to correct this you install CT2 to the live feed of your Sungrow inverter which provides the Fox inverter with all the information it needs to calculate loads, grid import and export.

It’s possible that CT1 is either clipped the wrong way round or is disabled in your inverter settings (this sometimes happens after a firmware upodate when first installed).

It would be helpful to diagnose if you could post an image of the power flow from the app, and also if you click oj daily production the graph it shows there as well.

This video shows how to check the CT’s are enabled correctly https://www.youtube.com/watch?v=WoOPmAlFTuc

[Safiq]

It sounds as if one (or both) of your CT’s are not being read correctly.

CT1 should be connected to the live feed of your supply meter and it measures the amount of power flowing in and out of the house, the battery then attempts to balance this to zero which is your house load.

If you have seperate solar panels, the inverter doesn’t know what the generation is and so it will get house load wrong, to correct this you install CT2 to the live feed of your Sungrow inverter which provides the Fox inverter with all the information it needs to calculate loads, grid import and export.

It’s possible that CT1 is either clipped the wrong way round or is disabled in your inverter settings (this sometimes happens after a firmware upodate when first installed).

It would be helpful to diagnose if you could post an image of the power flow from the app, and also if you click oj daily production the graph it shows there as well.

This video shows how to check the CT’s are enabled correctly https://www.youtube.com/watch?v=WoOPmAlFTuc

Thanks, the installer managed to drop by today on his way to another job and identified the issue. Because I have a controlled load meter on a separate phase, he had mistakenly wired the battery to that phase. Everything is sorted for now.
He did suggest that I look into moving my controlled-load hot water service onto the main phase and getting rid of the controlled-load meter altogether.
I’d be interested in hearing from anyone who has done this. Would I need a Level 2 electrician, or can a solar installer carry out the change? I understand he’s not allowed to touch the meter itself, so for that part I’d need to contact my energy provider