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solar power trickle charge

4K views 14 replies 9 participants last post by  colehankins 
#1 ·
Does anyone know the requirements for using a solar panel to keep a starting battery fully charged? I can''t find any kits that have it all. It looks like I would need the solar panel plus an inverter and auto shut off and other stuff that I don''t understand.
 
#2 ·
BMCald, I''ve never done all the math or calculated out an ideal system for recharging my boat battery, but I do have a system that works well for me.I have a 1 x 2 ft solar panel that I keep on the cabin top when at dock.I also have a small regulator that was sized for the panel.On a good sunny day,the panel provides about 3-4amps.This seems sufficient to keep the battery charged up,but not enough to overcharge.I''ve never had battery problems starting the engine,and my batteries are several years old.The West Marine advisor has some good information on sizing a system for your battery,etc.I think altogether I have about $175 in my system.
 
#3 ·
Last spring I bought a 10 watt panel that I just tie over my sail cover when I leave after the weekend. I run the wire between the hatch boards and hatch cover and plug it into a lighter outlet. I bought the "male" end of the lighter socket at Radio Shack and just soldered it on. I turn the battery switch to both and sadely leave for another week at work. So far, this has worked perfect.
I did do some reasearch before buying the unit. What I have found out (I''ll try and make a long story a little shorter) is that a liquid cell battery looses ~.2V/day without any draw. If it is left more than a week or so, throw in a bildge pump or so, well, you can do the math. Also, battery health is effected by periods of inactivity. In warm weather, in just after ~2 weeks a "crystallization" of the acid takes place, and if left long enough, will short out the plates. When you charge it, you reverse the chemical reaction. Also, if the solar cell is 10 watts (@~16V) you don''t need a regulator. From what I can find out, this approach should make the batteries last 2-3 times longer than letting them sit for the week and then charging them with the engine during the weekend. Also, it appears better to store your batteries outside in the winter and slow charge them about once/month.

We''ll see!

Mike in Noank
 
#4 ·
You may want to review Don Casey''s articles on this-- very informative. My approach is similar to the 2 previous respones.

I have a rigid 11watt for my house battery that does go thru a regulator. Have had for several months and working great. Permantly installed on the stern lazzerete.

This past week-end I added a flexible 5 watt for the starting battery. No regulator and I also just tie over the sail cover and run wire thru the hatch boards.

Both panels are US Solar and purchased from Sailnet.
 
#5 ·
So all that''s really needed is a 5-10W solar panel, and wire directly to the battery terminals? Don''t understand how the cigarette lighter plug in works, but like that for less messing around needed. My electric panel does have a cigarette lighter outlet that I use for a Megalight.

I just have one battery, used for starting the engine as well as house needs, which is a vhf, compass light and gps. All those are used from time to time. No electric bilge pump. Ran for a little better than 2 months without losing power. The diesel engine kept it charged up. But I''d like to start learning about solar, and this seems a good place to start.
 
#7 ·
Re; the cigarette lighter plug. All you need to do is buy the end(male)(can purchase at Radio Shack) that goes into the lighter receptacle(female) on your panel. Solder the male adaptor to the end of the leads on the solar panel..WATCH THE POLIARITY!!!SOLAR PANEL AND BOAT NEED TO BE THE SAME!! As long as your battery switch is closed you will "back feed" your battery through the cigarette lighter.
I just un-plug and stow my panel for the weekend.

Mike in Noank
 
#10 ·
Bruce:
To test polarity:
1. Connect negative lead on voltmeter (16VDC Scale) to an electrical ground.
2. Touch positive lead to Center Terminal of Lighter Socket. Meter should read +12VDC. If so, centre is Positive, outside shel is negative.
3. If not (above), Touch Positive Lead to Outside Shell. If reads +12VDC, outside is positive.
4. Connect Solar Cell output to male socket to match above results.
Regards
 
#11 ·
Connecting the solar panels to trickle thru the 12VDC lighter socket may simplify things, but that requires you to leave your battery switch in the closed position (as was stated).

My question: don''t most folks usually recommend that the switch stays open while the boat is unoccupied (and electric bilge pumps wire directly to the battery, bypassing the switch)?

Your thoughts on the pros/cons welcome.

Duane
 
#13 ·
While it''s true that it''s a "good idea to turn your battery switch off while away" this only ensures the batteries will not be drawn down if you leave something else on ie. radios, lights etc. When you leave the boat after the weekend :( it is important to develop a procedure to shut down the systems while your away.

Another small point; if/when you measure the voltage from the solar panel without a load attached to it, it will not measure the ~16volts needed to charge the batteries. Don''t be alarmed, it''s just the switch which prevents back feeding the solar panel has not closed. Everything will be OK once you plug into the lighter socket.

Mike in Noank
 
#14 ·
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.
 
#15 ·
Jap shack has diodes that help the solar panel. I think they are 1n1004 diodes that trap the current from leaking back from the batts during the night or lack of sunshine. Called avalanche or cascade diodes. They dont allow current to flow untill 12 vDC is reached. Put one diode in series with the positive lead, easy to put in the plug, and watch for polarity again. I also think the diode will take up to 3 amps, but check on that.
Cole
 
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