Hello everyone,
I discovered a detail about the SmartSolar MPPT 75/15 that doesn’t seem to be clearly described in the manual — and it might explain why some people (like me 
) can’t get the +5V/0V control via the RX pin (VE. direct port) to work.
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Observation
When the VE.Direct RX port is configured to
> “Load output on/off normal” or “Load output on/off inverted”
the Load output cannot be controlled via the RX pin if the Load output mode (in VictronConnect → Load output) is set to “Always on” or “Always off.”
Those two modes have higher priority, so the external RX signal (0 V / +5 V) is ignored and the load output remains permanently on or off.
However, if you select any algorithm-based Load mode such as BatteryLife or Battery voltage, the RX pin control immediately works as expected — 0 V turns the output off, +5 V turns it on (depending on normal or inverted mode).
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Hardware setup
I’m driving the RX pin via an NPN transistor (collector to RX, emitter to GND),w ith a 10 kΩ pull-up resistor to +5 V.
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Conclusion
It seems that in current firmware, the “Always on” and “Always off” Load modes have the highest priority and therefore override RX-based control of the load output.
This isn’t clearly stated in the manual, which might lead users to believe the RX pin can always switch the load output once it’s configured for Load output on/off normal/inverted.
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Question to Victron
Could you please confirm whether this priority behavior is intentional?
And for the other Load Output modes (BatteryLife, Battery voltage, etc.), does the RX signal act as an override or as a logical AND with the internal algorithm?
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Tested on SmartSolar MPPT 75/15 and 75/10 (newest firmware october 2025)