Hello, could you recommend me a suitable combined lightning current arrester of type 1+2 for BlueSolar or SmartSolar 150V? The typical arresters of this kind, e.g. DehnCombo are rated for at least 1kV DC. And what to do with the minus pole? Are those MPPTs buck converters and minus poles of input and output are the system ground and can be earthed? Or the input must be left floating and both poles have to be protected? Thanks.
You need to protect both the minus and the plus poles, neither of them is to be grounded. Surge protection devices with less than 1kV protection are very rare and usually not necessary.
I found the optimal solution. If the cables between the modules and inverter are screened, surge arrester of type 2 is sufficient. And these are available with low breakdown voltage. The screen, conducting a part of the lightning current, induces magnetically almost the same common-mode voltage into the cables as the potential difference between the module frame and the earth and reduces current through the cables significantly.
Once more back to the topic - does someone know the ground concept of the SmartSolar MPPT? Are the minus of the PV modules and minus of the battery internally connected? I suppose there is no galvanic insulation. In this case it would be reasonable to use different arresters, one about 300V for the plus (SmartSolar MPPT 250/100) and one with as low VBD as possible for the minus. Otherwise the one in the negative line would not trigger and the unwanted current would flow through the ground of the MPPT. My hardware is delivered yet, therefore I cannot check it with a multimeter.
Both minus terminals are galvanically connected through a current sensor (Hall-effect?). It means it makes no sense to use a typical Y-arrester or two identical MOVs. If the minus of the busbar is earthed, the plus pole arrester should be rated for the max. PV voltage and the one for the minus should have the clamping voltage as low as possible, just not a direct connection. I ordered two 100A diodes to put them anti-parallel there. And DehnGuard DG Mod 275 for plus.
