I’ve got a system with three SmartSolar MPPTs and a hydro generator charging an AGM battery bank, and often when the sun is out, the hydro generator (which has its own uninformed charge controller) will read the batteries at being higher than its target output voltage, which causes it to start freewheeling and making noise.
It can be difficult, and sometimes even unsafe for us to remove the hydro generator from the water and re-deploy it, so in the short term, we’ve just been manually disabling one or more of the MPPTs when we can’t take the hydro generator out of the water. This is a pretty brute force solution, though, and sometimes it drops the voltage lower than necessary, or requires constant management to toggle MPPTs back on if clouds come by.
I’d love to instead take advantage of the Cerbo and custom Node Red dashboard we have to tell the solar when we want to prioritize the hydro generator and to charge the system at a lower voltage. We could even do this programmatically based on hydro generator activity (we’ve got a SmartShunt monitoring its output voltage and current), but in the short term, I’m starting by looking for a way to do it with a manual toggle.
I tried looking through the available options with Node Red, and there doesn’t seem to be any voltage control offered over the MPPTs, either via the provided MPPT node, or even looking at the extended settings available with a custom node. There’s a way to adjust the charge current limit for each MPPT, but not the voltage settings, nor a way to force the controller into Float mode.
The broader system settings available in a custom node also don’t look helpful, with only the ability to adjust the DVCC current parameter (the adjustable voltage parameter seems to be for ‘managed’ batteries only, and has no effect for our AGM system).
A couple of ideas I’ve tried so far have been:
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Use a switch to disable shared current sense and manually send a current value lower than tail current to ‘trick’ the MPPTs into changing over to Float. This doesn’t respond immediately, however, as the MPPTs wait a minute or so to validate the current before changing modes, and it also doesn’t seem to work consistently across all three of our controllers. Adjusting the shared current sense setting also gets a bit messy and is something I’d like to avoid.
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Try and create a voltage-based PID control for the system current limit. This seems to get a bit messy, though, with the solar input constantly changing, and I don’t like constantly altering the system current limit to try and catch the voltage that’s controlled by the MPPTs own feedback loops.
I don’t really like either of these two solutions, and I’d much rather do something like tell the MPPTs to maintain a lower voltage temporarily, so their own feedback loops could handle providing the right amperage.
Does anyone know of a way to control voltage with Node Red?
Perhaps some way to mimic a BMS and just temporarily set a system-wide voltage limit when we want to prioritize the hydro generator?
