Join Date: Nov 2002
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solar power trickle charge
I use a 20 watt Solarex panel with no regulator. It works great, my batteries are almost always topped up when I arrive the next weekend. The 10 watt panel which I used previously didn''t seem to always quite keep up with the loads on my 33 foot sailboat.
I connected the panel directly to the two batteries through 2 diodes and 2 fuses. The diodes provide isolation between the batteries and also prevent discharging at night.
Leaving the battery switch on "Both" is not advisable. If the batteries are unequal, one will drain into the other and possibly both will be destroyed. I''ve had that happen. It''s also a possible fire hazard. If a battery shorts out, the other one will pump a lot of current into the bad one, heating it up. Not a good idea while the boat is unattended.
You can use just about any diode from Radio Shack as the current is low (less than 2 amps for a 20 watt panel). The fuses should be about 2 amps. The banded end (cathode) of each diode should be connected to the positive terminal on each battery through a fuse. The other ends (anodes) should be connected together and to the positive output from the solar panel. The negative output from the solar panel is connected to the negative terminals on both batteries. Using two diodes prevents any measurable current flow between the batteries while allowing the panel to charge both batteries.
Returning to the boat on a sunny afternoon I''ve measured nearly 13 volts at the batteries, but that doesn''t seem high enough to cause overcharging or loss of electolyte. I get five years out of my batteries and use this arrangement during the winter so I don''t have to take the batteries off of the boat.