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francesco-marzulli asked

Panels number for MPPT 250-70Tr

PV panels: 390W; Vmpp=40,8V; Impp=9,56A; Voc=49,3V; Isc=10,03A; -0,27%/°C; 0,04%/°C.

System battery:48V

With this panels, already with Tmin = 0 ° C, it would be Voc = 52.6V (with Tmin= -10°C it would be Voc=54V, only with Tmin=20°C it would be Voc=50V) and therefore a maximum of 4 panels can be connected in series for MPPT 250-70Tr: con you confirm this?

For MPPT 250-70Tr, the (Isc)max = 35A, so a maximum of 3 strings (of 4 panels) can be connected to it: it's right?

I know my question is a weird one but I ask (to understand some things better): what would happen by connecting 5 panels in series instead (for Vmpp: 40,8Vx5=204V < 250V)?

What problems would arise? Can there be any damage to MPPT? The system will not work properly?

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klim8skeptic answered ·

What problems would arise? Can there be any damage to MPPT? The system will not work properly?

You can never, ever expose your mppt to higher array voltages than it's design is rated for (at expected local low temperatures).

Once the blue smoke escapes the blue box, it is an expensive paper weight.

>Victron online MPPT calculator. <

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francesco-marzulli avatar image francesco-marzulli commented ·

Thanks @klim8skeptic, I fully agree with your considerations, of course... I only ask a confirmation for the calculations I have made...

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