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Solar Panel system to keep seldom-used truck battery charged

Former Member

Hello all!

 

I have a pickup truck that I only drive maybe once or twice a week. Sometimes a week will pass between uses. I bought a NOCO 2.5W solar panel kit to keep it topped off and it does OK, but during this cloudy and cold winter I had to charge the battery once with an external charger.

 

So I'm thinking that I need a larger solar panel. I can mount it in the bed of the truck, right behind the cab, pointing straight up. (I plan to hinge the mounting so I can just fold it up to make room for anything I need to haul in the truck, and to protect it.)

 

I'm looking for ideas as to how much of a panel I need and should I incorporate a PWM charge controller, and maybe any other automotive specific things I might need to know.

 

Thanks for any input you can give me!

  • 0

    A different idea: use mirrors and position carefully to increase the lumens on the current solar cells.

    Clem

  • 0

    clarkdv For this kind of application, where we can assume that the battery is fully charged after you drive the vehicle, I would go for a 15 or 20 Watt panel.  Even with this small current, there is still the possibility of over-charging the battery - so some kind of control is needed.  I would not bother with a PWM charge controller - what you really want to do is limit the charging voltage to 13.8 to 14 V.  The current from a 20W panel in the brightest sun should not exceed 2A (more likely 1A) so I would just use a zener diode to dump the excess into a resistive load.  There are 3A rated controllers (for about 10 to 15 USD) that do this, but they tend to limit at 14.2V, which is a bit on the high side.  Don't forget you will need a (Schottky) diode to prevent the battery discharging into the panel at night!