Hello. The datasheet for Multi RS Solar states that the PV start-up voltage is 120 V. In 1.16 firmware update I’ve noticed that the lower voltage limit of MPPT was decreased from 85 to 65 V. Is there any chance that the start-up voltage will be decreased too in future updates?
I would appreciate if the start-up voltage would be decreased to battery voltage + 5 V like it is in standalone MPPT controllers. That would make it possible to use the Multi RS Solar with small solar arrays.
It would be great if someone from the engineering team could tell if such change can theoretically be done via a software update or is MPPT designed in such a way that it will not be able to start at a much lower voltage.
They are saying that the startup voltage is 120V, but in fact is around 90V. You can see by looking at the graphs on VRM.
Once the MPPT is started, it can go as low as 65V, indeed.
But because the maximum short circuit of each MPPT is about 16A, with an operational limit of about 13A, it will mean that you can’t parallelize PV strings like in the case of SmartSolar range of solar chargers.
That 13A limit will mean that you can only have one PV string at most per MPPT, because most panels have such short circuit current.
And a 13A limit at such low start voltage like you want (approx. 55V) will mean a very low generated power which will be just inefficient.
Different approach, by just making a long string rather than parallelizing multiple short strings.
Lower current of long strings will mean smaller cables.
Thank you for the information. The system that you’ve described is exactly the kind of solar array that I have - just two panels in series and BlueSolar 150/35. Not much, but better than nothing.
There may be an option in the future to install additional two panels facing a different direction, so I was wondering if I’ll have to buy another MPPT for them or will manage to somehow make Multi RS work with them.
Regarding the max current. What’s interesting is that the logs of BlueSolar tell that on some days (cold air, plenty of solar and a bit of clouds) the max current was up to 17A even though the panels have short circuit current of 14A max per datasheet, so I’m curious how Multi RS would behave in such case. Is it drawing all the amperage it can get until it will overload and shut down or is there a safety mechanism that would cap the current to 13 or 16A?
It was charging the batteries at 17A, but the PV side was carrying 12.9A (869W divided by 67.11V, assuming Pmax and Vmax were happening at the same time) so no, your panels did most likely not exceed their nameplate Isc
You should use a second MPPT if the panels are facing a different direction. Connecting them into one string would lead to the shaded panels to impede current flow trough the whole string
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