[VAC] Blocking Diode

[Paul Farley <farley@xxxxxxxxxxx>]

Hi All,
I recently picked up a solar powered fan/vent combination at a swap
meet.    It is designed to be installed on the roof of a camper, trailer
or van.   Ihave not yet measured it's output, approximate sixe is 15'
x15".   I am considering  adapting the panel to power a 12v 300ma
computer fan to run air over the evaporator coil of my dometic on very
hot days.   While listening to all the talk on battery chargers I
decided this same panel would make a nice trickle charger.  Does anyone
know the proper blocking diode I would install in line to avoid battery
discharge at night?
Thanks in advance, Paul