I plan to be on a mooring next season. As such, I'm thinking of buying a solar panel to keep my two batteries fully charged. (1) What are the minimum amps and volts I will need to do this? (2) what is the recommended way to connect the panel to the batteries (or can this be done by simply plugging the panel into a cigarette lighter outlet? (3) must the panel have some sort of diode to protect the batteries from overcharging or will a minimal trickle charge solar panel do this automatically? Any other advice or cautions on this subject would be appreciated.
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Solar Panels
Warren In order to answer your questions, you need to describe your battery system a bit more. You say "fully charged." The answer is basically what's going in vs. what's coming out. How big a battery bank do you have? How much do you drain it between charges (either solar or engine)? Your starting battery most always will be full (only uses 2 amp hours to start the engine) so you want to charge your house bank with the solar panels. You can size the solar panel(s) to merely offset the self discharge of your batteries (assuming wet cells), or you can make it bigger, in which case you will need a regulator. Diodes waste volts. You can connect the solar panel(s) directly to your house bank, or through the 1-2-B switch (but that'd use more wiring and connections and thus more voltage drop). Lots of options for you here. I recommend that you read the West Marine Advisor on solar cells. Very helpful for sizing and understanding the concepts. UniSolar and basically a Google search on solar panels will provide you with a wealth of information that's too much to repeat here. Then design the system you need for how you intend to use your electrical system. Stu
Warren In order to answer your questions, you need to describe your battery system a bit more. You say "fully charged." The answer is basically what's going in vs. what's coming out. How big a battery bank do you have? How much do you drain it between charges (either solar or engine)? Your starting battery most always will be full (only uses 2 amp hours to start the engine) so you want to charge your house bank with the solar panels. You can size the solar panel(s) to merely offset the self discharge of your batteries (assuming wet cells), or you can make it bigger, in which case you will need a regulator. Diodes waste volts. You can connect the solar panel(s) directly to your house bank, or through the 1-2-B switch (but that'd use more wiring and connections and thus more voltage drop). Lots of options for you here. I recommend that you read the West Marine Advisor on solar cells. Very helpful for sizing and understanding the concepts. UniSolar and basically a Google search on solar panels will provide you with a wealth of information that's too much to repeat here. Then design the system you need for how you intend to use your electrical system. Stu
Best investment yet!
Warren, I'm on a mooring in the upper Chesapeake and have a 6 watt solar panel wired directly, thru separate diodes and a connector, to both batteries. I simply plug it in and lay it on a cockpit seat when I leave the boat. Batteries are kept at full charge all of the time, best investment I have made yet! Brian, '88 272LE "Hosanna"
Warren, I'm on a mooring in the upper Chesapeake and have a 6 watt solar panel wired directly, thru separate diodes and a connector, to both batteries. I simply plug it in and lay it on a cockpit seat when I leave the boat. Batteries are kept at full charge all of the time, best investment I have made yet! Brian, '88 272LE "Hosanna"
Diodes
You need to have a diode. Solar panels will charge your batteries during the day, but will discharge them at night. The diode is like a one-way valve. West Marine sells a little voltage regulator with a built in diode for $29.95 It works well. Do a serch on Google. There is a lot of good info on solar panels... Ron
You need to have a diode. Solar panels will charge your batteries during the day, but will discharge them at night. The diode is like a one-way valve. West Marine sells a little voltage regulator with a built in diode for $29.95 It works well. Do a serch on Google. There is a lot of good info on solar panels... Ron
Diodes may not be Necessary
A diode is not necessarily desireable. A diode, besides keeping the battery from draining at night, causes a voltage drop when charging. For a small solar panel, the loss in charging is more than the drain at night. I have a straight 10w solar panel with no diodes or regulator which has kept my 100ah battery charged for two years with no problems. The only time the battery has discharged is when I bring it home and put inside for annual work.
A diode is not necessarily desireable. A diode, besides keeping the battery from draining at night, causes a voltage drop when charging. For a small solar panel, the loss in charging is more than the drain at night. I have a straight 10w solar panel with no diodes or regulator which has kept my 100ah battery charged for two years with no problems. The only time the battery has discharged is when I bring it home and put inside for annual work.
Good Point Dan
My panels are a total of over 60 watts and therefore need a regulator and diode.... Ron
My panels are a total of over 60 watts and therefore need a regulator and diode.... Ron
Solar Power Charging, III
Stu: Thanks for all the info and advice re solar panels. When I mentioned that I thought the fuse would eat up some voltage I was referring to my belief that any additional connection (i.e, two crimps to put a fuse in the circuit) would decrease the amount of volts going to the battery, albeit by a minor amount. Although the panel I bought has a built in diode, I can find no indication that it also has a fuse in the wiring. I plan to contact the maker and ask....
Stu: Thanks for all the info and advice re solar panels. When I mentioned that I thought the fuse would eat up some voltage I was referring to my belief that any additional connection (i.e, two crimps to put a fuse in the circuit) would decrease the amount of volts going to the battery, albeit by a minor amount. Although the panel I bought has a built in diode, I can find no indication that it also has a fuse in the wiring. I plan to contact the maker and ask....
V.D. & Connections
You are absolutely correct - every termination adds some Voltage Drop to the circuit. Poorly made, or corroded connections may present as much as 0.03 Ohms to the circuit - whereas excellent terminations might add 0.001 Ohms. The larger the solar panel, the more significant this may become. Using a 15 Watt panel, the blocking diode will Drop 0.70 Volts, and the (2) Terminations may drop between 0.002 and 0.06 Volts. At 150 Watts, the Diode still drops 0.70 Volts, whereas the terminations now Drop as much as 0.12 Volts. So, as you indicated the Voltage Drop is "there", but it's not really significant - except as a cumulative thing (The diode + all the wire + all the connections). (note: Voltage Drop = Amps x Ohms) Regards, Gord
You are absolutely correct - every termination adds some Voltage Drop to the circuit. Poorly made, or corroded connections may present as much as 0.03 Ohms to the circuit - whereas excellent terminations might add 0.001 Ohms. The larger the solar panel, the more significant this may become. Using a 15 Watt panel, the blocking diode will Drop 0.70 Volts, and the (2) Terminations may drop between 0.002 and 0.06 Volts. At 150 Watts, the Diode still drops 0.70 Volts, whereas the terminations now Drop as much as 0.12 Volts. So, as you indicated the Voltage Drop is "there", but it's not really significant - except as a cumulative thing (The diode + all the wire + all the connections). (note: Voltage Drop = Amps x Ohms) Regards, Gord
V.D. @ Connections
You are absolutely correct - every termination adds some Voltage Drop to the circuit. Poorly made, or corroded connections may present as much as 0.03 Ohms to the circuit - whereas excellent terminations might add 0.001 Ohms. The larger the solar panel, the more significant this may become. Using a 15 Watt panel, the blocking diode will Drop 0.70 Volts, and the (2) Terminations may drop between 0.002 and 0.06 Volts. At 150 Watts, the Diode still drops 0.70 Volts, whereas the terminations now Drop as much as 0.12 Volts. So, as you indicated the Voltage Drop is "there", but it's not really significant - except as a cumulative thing (The diode + all the wire + all the connections). (note: Voltage Drop = Amps x Ohms) Regards, Gord
You are absolutely correct - every termination adds some Voltage Drop to the circuit. Poorly made, or corroded connections may present as much as 0.03 Ohms to the circuit - whereas excellent terminations might add 0.001 Ohms. The larger the solar panel, the more significant this may become. Using a 15 Watt panel, the blocking diode will Drop 0.70 Volts, and the (2) Terminations may drop between 0.002 and 0.06 Volts. At 150 Watts, the Diode still drops 0.70 Volts, whereas the terminations now Drop as much as 0.12 Volts. So, as you indicated the Voltage Drop is "there", but it's not really significant - except as a cumulative thing (The diode + all the wire + all the connections). (note: Voltage Drop = Amps x Ohms) Regards, Gord
An alternative
that works well for my situation is the "CycleCharger", the smallest solar charger RadioShack sells. I believe it is the same unit as the BatterySAVERPLUS sold by BoatUS and WestMarine in the 1.8 W size. Since I don't sail much at night, the only draw on my battery is the knotmeter and depthsounder. This charger will top up the battery if I don't sail every day, with the added advantage of being small enough that it can be mounted off the back of the transom using two over-the-door clothes hanger brackets. That means I can leave it wired up all the time, it's never in the way, and I never have to pull the battery or charge it at the dock. Several weeks ago I ran the battery down to about 10.5 volts, and within a couple of days it was all the way back up. An excellent accessory is a portable rechargeable booster pack ("jumper box") that you can carry home and recharge from time to time. I used one for years to power the lights on my previous boat - one charge would last a couple of nights (small boat) and it had the added advantage of being easy to carry. It paid for itself one night after a day of racing when my friend left his ignition on and locked us out of his coded-entry Explorer (you can't get in when the system has no power).
that works well for my situation is the "CycleCharger", the smallest solar charger RadioShack sells. I believe it is the same unit as the BatterySAVERPLUS sold by BoatUS and WestMarine in the 1.8 W size. Since I don't sail much at night, the only draw on my battery is the knotmeter and depthsounder. This charger will top up the battery if I don't sail every day, with the added advantage of being small enough that it can be mounted off the back of the transom using two over-the-door clothes hanger brackets. That means I can leave it wired up all the time, it's never in the way, and I never have to pull the battery or charge it at the dock. Several weeks ago I ran the battery down to about 10.5 volts, and within a couple of days it was all the way back up. An excellent accessory is a portable rechargeable booster pack ("jumper box") that you can carry home and recharge from time to time. I used one for years to power the lights on my previous boat - one charge would last a couple of nights (small boat) and it had the added advantage of being easy to carry. It paid for itself one night after a day of racing when my friend left his ignition on and locked us out of his coded-entry Explorer (you can't get in when the system has no power).
The fuse is to prevent...
excessive current when the + cable from the battery to the panel is shorted to ground. In that case, the current would not flow through the panel and thus the internal fuse would not prevent the high current. I mounted the same 5W panel in my boat (off the water) this winter because they are not keeping electricity running in the yard, for safety reasons, and I did not feel like removing 420 Amp/h worth of AGM batteries from the boat. I have been told that as long as the batteries remain fully charged, they will do OK in the cold. Any comments?? I installed a fuse but did not install the diode. So far I have been checking the battery voltage and it seems holding at full charge but as winter progresses, the amount of day light in Massachusetts gets lower and lower. Any body knows how much current flows back at night across a solar panel without diode?.
excessive current when the + cable from the battery to the panel is shorted to ground. In that case, the current would not flow through the panel and thus the internal fuse would not prevent the high current. I mounted the same 5W panel in my boat (off the water) this winter because they are not keeping electricity running in the yard, for safety reasons, and I did not feel like removing 420 Amp/h worth of AGM batteries from the boat. I have been told that as long as the batteries remain fully charged, they will do OK in the cold. Any comments?? I installed a fuse but did not install the diode. So far I have been checking the battery voltage and it seems holding at full charge but as winter progresses, the amount of day light in Massachusetts gets lower and lower. Any body knows how much current flows back at night across a solar panel without diode?.
Attachments
Solar Cell Blocking Diode
You really need to have the blocking diode installed. Without the diode, at night current will flow back through the solar cell. This will cause self heating of the solar cell and could result in damage to the solar cell. Why take the chance, and also lose the power you stored during the day
You really need to have the blocking diode installed. Without the diode, at night current will flow back through the solar cell. This will cause self heating of the solar cell and could result in damage to the solar cell. Why take the chance, and also lose the power you stored during the day
JoAnn, the ICP panels have it 
With a little research *! I found that the ICP battery saver Pro 5-watt has built in blocking diode. Adding an extra diode is not needed and will drop the available voltage for charging. I also learned that AGM batteries lose less than 2% of its charge per month. For a 400 Amp-Hour bank, it comes out to be about 11 mA of continuous drain (400*0.02)/(30*24). A 5 watt charger puts out 333 mA at 15 V at full sun. This means that one would need 1/30 of day (less than one hour) of sun to make up for the loss. I actually measured a charge of 150 mA into the batteries with full sun at 2 PM last weekend. Thus, at that rate I would need less than 2 hours of sun per day. Even during the worst winter in New England we get at least that much sun in average per day.
With a little research *! I found that the ICP battery saver Pro 5-watt has built in blocking diode. Adding an extra diode is not needed and will drop the available voltage for charging. I also learned that AGM batteries lose less than 2% of its charge per month. For a 400 Amp-Hour bank, it comes out to be about 11 mA of continuous drain (400*0.02)/(30*24). A 5 watt charger puts out 333 mA at 15 V at full sun. This means that one would need 1/30 of day (less than one hour) of sun to make up for the loss. I actually measured a charge of 150 mA into the batteries with full sun at 2 PM last weekend. Thus, at that rate I would need less than 2 hours of sun per day. Even during the worst winter in New England we get at least that much sun in average per day.
never to big
I have experience with solar and wind power. In my opinion solar gives me more service. I have 2-50 watt panels on a sunsaver 10amp regulator. Regulator has diode to prevent bleeding back at night and also stops damage to battery in case of overcharge. Why I say never to big with reference to refridgeration and the onslaught of electronics seems that we are always in the need of electrical power. Darrel Vancouver Island, BC, Canada
I have experience with solar and wind power. In my opinion solar gives me more service. I have 2-50 watt panels on a sunsaver 10amp regulator. Regulator has diode to prevent bleeding back at night and also stops damage to battery in case of overcharge. Why I say never to big with reference to refridgeration and the onslaught of electronics seems that we are always in the need of electrical power. Darrel Vancouver Island, BC, Canada
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