Fox Inverter Force Charge/Discharge rate

[AndySmithers]

Not an issue, as such, just an observation on the Fox Inverter (well, my H1 G2 anyway).
Using Tony's kW/W converter to translate for the force charge/discharge works fine, of course.
But, on my inverter, using this with the Low Power Export switch is pointless.
The reason is that the Force Discharge power in the Modbus integration is not actually the battery discharge rate but the inverter export power.
PredBat today wanted to Force Export at 1.5kW (Low Power Export) to slowly discharge the battery to grid - adding to the existing solar export, so it set Force Discharge power to 1.5kW and set the Fox inverter to Feed-In. All good.
However, the sun was shining to the tune of 3kW.
So the inverter duly set the Export power to 1.5kW...and then the remaining 1.5kW could only go to the battery.
The net result was that even though it was in Export (Feed-In) mode, the battery was charging from solar!

Now, as far as I can see, there's no problem with using low power Force Charge but low Power Force Discharge is pointless for this inverter.
Someone please correct me if I'm wrong.

[WyndStryke]

Perhaps number.max_discharge_current could be used? This is a BMS control, based on amps, and presumably the battery voltage would need to be used in the automation to translate from W on the predbat side to A in the BMS. (Not sure which battery voltage, nominal or the actual voltage).

number.force_discharge_power and number.max_discharge_current simultaneously act as limits - whichever is the bottleneck at any moment will control the output.

In my own personal automations I've only ever used the inverter control, but I do dynamically adjust it by the current PV when needed. So I have never tried to play with max_discharge_current.

I have a vague memory of someone mentioning that predbat also allows the charge and discharge rates to be controlled via current, so perhaps a translation layer isn't required (or I might be mis-remembering, which is entirely possible).

Note that there is also a sensor.bms_charge_rate and sensor.bms_discharge_rate - this can be queried to see if the BMS itself is restricting the charge rate (for example, when the battery is very cold, or is near 100% SoC).

The last time this was discussed, it was in the middle of winter, so I don't think PV was really affecting things enough to be noticeable at the time!

[AndySmithers]

Thanks for the pointers, WyndStryke, I will give these all a look.
Your best idea, I think, is adjusting the charge rate based on PV output to avoid the issue I had.
I'm not entirely sure what the real world value is of controlling the charge/discharge rate like this, rather than simply letting the inverter figure it all out and just export/import at full power.

Of course, the FoxCloud service now has the Scheduler function, which does allow you to set FD and FC powers.
It's a shame we can't get a ModBus update from Fox so we can actually use these registers for PredBat.