Controlling Pylontech charge rate and target SOC for Sunny Island overnight charging

[jonc_uk]

I am finally working on a method to limit/control the overnight charging of my Pylontech US5000 stack.

I have 3x Sunny Island 8.0H in a 3-phase setup which can charge at 18kW during the overnight cheapslot. I also have 1x ME3000SP which is controlled via Home Assistant to assist charging if the stack requires extra charge power to reach 100%.

Now we move into the sunnier months, there will be times when the batteries don't need to be at 100% by the end of the cheapslot - the sun will get them there during the day.

With my previous setup of 4x ME3000SP, I would set a lower target SOC to allow for the additional charging in the day. However, the Sunny Islands are not capable of managing this, even though the documentation (and even some people in support) think they will do.

The method of controlling the charging seems to be by interfering with the battery CAN data sent to the inverters. I know Tinbum has already done this.

I think the steps would be:

* At the start of the charge period, look at the solar forecast for the following day.
* Calculate the target SOC required (plus add a safety margin?)
* Calculate the required charge current and alter this within the CAN message sent to the Sunny Islands.
* Maybe check the solar forecast periodically during the charge window to see if it has changed and recalculate above.

In addition, I can also set a lower max voltage of 52.5V as Tinbum does for better battery health. Then I need to decide if/when I force a full charge to 100% with a higher (Pylontech published = 53.2V) or wait for the batteries flag this to the inverter.

I already have a solar forecast in Home Assistant so I think I can use this. I could also fall back on a schedule by month of target SOC.

I have the hardware and am already reading the battery CAN data.

Am I missing anything? Is this the correct way to control/limit the charging?

[nowty]

Are you on an export tariff ?

I just dump power to the grid as soon as my 5:30 cheapslot ends.

Example from yesterday, I use a pump and dump methodology and use my ME3000SP's to take some of the strain off my expensive Sunny Island.



As we approach into summer I even export ALL night, I've even exported for 3 days non stop at one time last year.

[jonc_uk]

Are you on an export tariff ?

No - all self-install

Reducing the charge current will also make the inverters more efficient and reduce their heat output. They are located in a plant room which currently bleeds heat to the surrounding rooms - not ideal in the summer.

[MrPablo]

This is exactly what I'm doing with my self install setup.

I also have logic that calculates average house usage over the last 60 days (in 30 minutes periods).
I then set a minimum SOC target (20%) and calculate how much to charge the battery using average usage and solar forecast.
It works well, preventing me from charging the batteries more than needed, but still with a useful buffer.

Adjusting the CAN isn't too difficult, lots of projects on GitHub.
I set minimum charge power to 1200w and just calculate the amps needed.

[Tinbum]

I also do all that with my setup using the Teensy and node red.

[jonc_uk]

I also do all that with my setup using the Teensy and node red.

Do you just adjust the charge current reported to the inverters then? Do you ever mess with the reported SOC?

[Tinbum]

I use my Elteks for the battery charging at night. Yes, within the teensy I alter the charge current settings based on the SOC I want to reach, the predicted KWh for the day and the length of the time slot. Every half hour the teensy recalculates the charge current and adjusts the Elteks.

If I was using the SI to charge during the cheap rate I would adjust the SOC value sent to the SI.

[jonc_uk]

If I was using the SI to charge during the cheap rate I would adjust the SOC value sent to the SI.

Ah, interesting. Why SOC rather than Charge Current?

[Tinbum]

I'd likely do both.

I'd calculate an average current required over the time of the cheap rate and also change the soc of charge sent to the inverter so it definitely stops the charge at the required SOC. ( Thinking though, you could actually do that in the control mechanism to set the charge rate at zero, so no need to alter what the inverter sees.)

[jonc_uk]

Ok thanks.

Not too far away from trying it out..