Hello developers,
Not necessarily a bug, but an annoying issue which I believe it's better to raise it now, before releasing the feed-in capable firmware.
According with the firmware, through the Victron register VE_REG_LINK_CHARGE_CURRENT_LIMIT you can specify the maximum current the charger must supply.
1. If you have the MultiRS on Remote Control (GX control) and you periodically send a value on this register, I've observed the following behavior when the SOC is close to 100%, when the trackers are working in the current limited mode.
1.1. If you send to 0x2015 register a value of 0 (zero), the MultiRS will drive the MPPTs to only supply the necessary power to the AC Out loads. That's normal.
When the loads are smaller than the solar capability, the MPPTs output is equally distributed between MPPTs.
Eg: if your loads are 2000W and solar is plenty (over 2000W), then the MPPTs are producing equally 1000W per MPPT.
1.2. If you send to 0x2015 register a value different than 0 (zero), the MultiRS will drive the MPPTs to supply the AC loads and to produce the energy necessary to feed-in and/or keep the batteries on the float level.
Now, if you have more than plenty of solar, the MPPTs are driven in an unbalanced manner, meaning the power supplied by one MPPT will be bigger than the other MPPT (who can even be 0 (zero)).
Eg: if you have over 2000W of solar and the loads are 2000W, one MPPT could be at 2000W and the other MPPT can be at 0W.
At the beginning, the MPPTs seem to be equally balanced, but from tracking to tracking, one MPPT will start to increase its output and the other will decrease the output, until the above imbalance: one to cover all and the other at 0. Didn't find a logic which one will produce and which will be idle. Seems to be random.
2. If you have the Multi RS to work on its own, without GX control, it will always work in this unbalanced mode.
You will say: Hey, that's OK, as long as it's below the maximum MPPT capability, all is withing the limits.
But:
a) An imbalance between PV strings will keep on string hot - because of the production - and the other much cooler. Uneven wear and tear on panels.
b) The producing MPPT will be "running hot", sometimes near it's maximum, while the other will "run cold". Wear and tear on the working MPPT electronic components, which, if balanced, could run at half power/temperature rather than max power/temperature.
c) The AC/DC/MPPT section fan, which's speed is based on load, will work on full speed, because the power of the working MPPT approaches maximum. If the MPPTs were to be balanced, the fan speed will be half. So wear and tear on the fan too, not to mention the fan noise - quite loud.
Could it be made to work balanced, no matter the working mode?
Is this (1.2) the intended behavior?
Thank you!
Alex
