Externally control Load Output of MPPT Charge Controller

DIY
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1

Hello together,

In my system the inverter currently throttles its output under high load due to temperature. Now I would like to install an additional cooling fan that should turn on automatically if the inverter reaches 60°C. I was thinking the best way to do this is to use a 24V fan and drive it via the load output of my MPPT 75/15 charge controller through a voltage regulator. I already have a few ideas of how to implement this, but each has its downsides and I would like to hear whether you have different / better ideas than myself.

The situation is that the VE.Direct port of my charge controller is connected to an UART port of an ESP32 which can send and receive data through MQTT to communicate with my Home Assistant server and I have implemented the HEX Protocol, so I can control the charge controller using set-commands. In the best case I would like to keep the low-voltage protection logic from the charge controller, but since the fan will only draw very little current even in case of a failure it will take a long time to drain my battery.

I have already thought of the following possibilities (some may not work):

  • Leave the load output setting at “user defined algorithm 1” and control the load output by directly setting its state register 0xEDA8 to 0x00 or 0x01 - This seems to not work since the register appears to be read-only, but maybe there is a workaround I don’t see right now?
  • Switch the load output setting between “Always off” and “user defined algorithm 1” by setting its register 0xEDAB - I expect this to work, but turning the load output on would have a 2 minute delay. I was thinking to alternatively switch to “Always on” which is supposed to have no delay, however when I tested it the delay was still present.
  • Set the load output setting to “user defined algorithm 2” and control the state by setting the high level register 0xED9D to the low level to turn off and to something very high to turn on - I expect this to work too, however it would still have this 2 minute delay before a state switch becomes active.
  • Set the RX pin mode to “Load output on/off remote control” and control the state by controlling the idle state of the TX pin of my ESP32 - I expect this to work as well, but I was wondering wether I can still send HEX protocol commands to the charge controller with RX pin mode set to “Load output on/off remote control”. In case of the TX port settings the manual explicitly specifies which ones can be used in parallel to standard communication, unfortunatly it does not do so for the RX port settings.

Of course if you have yet another idea of how to achieve this or have even done something similar yourself in the past I would be very happy to hear about.
Thank you very much and best regards,
Triple_S

2

Hello again,

I think I have now found the perfect solution for the problem myself. I noticed that while changes to the load output logic have a 2 minute delay until they become active, the streetlight function does not and since the streetlight function works together with the regular load output logic in a AND-manner, the battery protection can remain always active. With default configuration the streetlight function will never turn the load output on because both the sunset and sunrise actions are to keep the light off. Thus, if I want to disable the load output, I simply turn the streetlight function on and to enable the load output I turn the streetlight function off falling back to the regular load output logic. Both actions take effect immediatelty without any delay.

Best regards,
Triple_S