Backfeeding panels

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Regular Member

Joined: 10/02/2015
Location: United Kingdom
Posts: 48
Posted: 06:30pm 27 Oct 2020      

if you're connecting your panels to the battery via a controller then the controller should have it's own diode I think (excepting Murphy's Friends' multiple assorted strings situation).

If connecting direct to battery like me, then the diode should be rated for > max battery volts, and I'd recommend at least 1.5 times Imp of the panel(s) - although that's probably overkil.

I actually use a Mosfet wired so the 'body diode' of the mosfet is conducting when the solar panels are generating; i built a simple op-amp circuit to turn the mosfet on when the voltage across it is >0.1v so I don't lose significant voltage in the Vf diode drop. If the circuit should fail the mosfet would just work as a regular diode but get warm (it's on a small heatsink).

It's a simple enough circuit, but as you're running the mosfet 'backwards' it can be a bit confusing to setup, especially as to use an n-channel mosfet you either have to put it in the -ve line or run the op-amp off a supply 'above' the battery +ve terminal voltage (probably easier to use a P-channel if you want to put it in the B+ line, but they're not as good).