How many watt solar panel would be needed to continually maintain a charge for a 2 battery bank system (2-12 volt batteries)? Both are connected together and run both house and starting needs. If hooked up to the positive of one battery and the negative of the other will it charge both? Thanks
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charging by the sun
In order to really answer your question, I need to know the amp-hour ratings of your batteries. But I can give you a partial answer: if you have your pair of batteries connected with the positive of one hooked to the positive of the other, and the negatives hooked to each other, you're in parallel--and you can charge both at once with a 12V charging panel (which really should put out about 13.6 to 14V to charge your system efficiently). In order to charge two batteries that are wired in parallel, you only need to connect to one (either one!) positive terminal and one negative terminal. However--I'd be surprised if you just had the two batteries connected in parallel. Typically the batteries connect either through a rotary selector switch so you can use one, the other, or both together, or they connect through a specialized diode (think of it as an electrical one-way valve) system to isolate one battery from the other. Let me know more and I'll try to help.
In order to really answer your question, I need to know the amp-hour ratings of your batteries. But I can give you a partial answer: if you have your pair of batteries connected with the positive of one hooked to the positive of the other, and the negatives hooked to each other, you're in parallel--and you can charge both at once with a 12V charging panel (which really should put out about 13.6 to 14V to charge your system efficiently). In order to charge two batteries that are wired in parallel, you only need to connect to one (either one!) positive terminal and one negative terminal. However--I'd be surprised if you just had the two batteries connected in parallel. Typically the batteries connect either through a rotary selector switch so you can use one, the other, or both together, or they connect through a specialized diode (think of it as an electrical one-way valve) system to isolate one battery from the other. Let me know more and I'll try to help.
to maintain a charged battery bank
a 5 to 10 watt panel would be suffecient, however the batteries need to be close to fully charged to start with. If you want to recharge the bank after say a weekend of stereo, gps, anchor lights, etc. it will take a much larger panel to do this. You need to know how many amp/hours have been drawn from the batteries and size the panels to replace this amount plus about 15%-20% to account for effeciency loss. There are lots of threads about this in the archives.
a 5 to 10 watt panel would be suffecient, however the batteries need to be close to fully charged to start with. If you want to recharge the bank after say a weekend of stereo, gps, anchor lights, etc. it will take a much larger panel to do this. You need to know how many amp/hours have been drawn from the batteries and size the panels to replace this amount plus about 15%-20% to account for effeciency loss. There are lots of threads about this in the archives.
RE: Solar Battery Question
Nichole, I used to have a boat on a mooring at Port San Luis for 3 years and found that a 5 watt solar charger kept my two 12 volt batteries fully charged, if they had a good charge to start with. There is no need for a regulator with a 5 watt solar panel. The solar panel kept the two batteries at about 13.25 volts. Michael
Nichole, I used to have a boat on a mooring at Port San Luis for 3 years and found that a 5 watt solar charger kept my two 12 volt batteries fully charged, if they had a good charge to start with. There is no need for a regulator with a 5 watt solar panel. The solar panel kept the two batteries at about 13.25 volts. Michael
David....
sorry I didn't give more detail. Your right, I do have a rotary selector switch so you can use one, the other, or both together. It is currently set up with both batteries connected in parallel and I run off the "1" setting only. I'm planning on adding another battery for just starting next season and use the two in parallel for the house. Thanks for the details to both you and Reudi. Hope this helps.
sorry I didn't give more detail. Your right, I do have a rotary selector switch so you can use one, the other, or both together. It is currently set up with both batteries connected in parallel and I run off the "1" setting only. I'm planning on adding another battery for just starting next season and use the two in parallel for the house. Thanks for the details to both you and Reudi. Hope this helps.
Solar charging 2 banks
Nichole, I used to keep a catalina 30 at Port San Luis (california) on a mooring for 3 years. I had a 5 watt solar panel that I hooked up to my batteries and it kept them charged great. I had to put the selector switch to 'all' so that they were paralleled. It kept the voltage at about 13.25 volts. The batteries need to be fairly well charged to start with - i.e., the 5 watt panel will not charge a dead battery or nearly dead battery. But it does a great job of keeping ahead of the natural discharge. Michael
Nichole, I used to keep a catalina 30 at Port San Luis (california) on a mooring for 3 years. I had a 5 watt solar panel that I hooked up to my batteries and it kept them charged great. I had to put the selector switch to 'all' so that they were paralleled. It kept the voltage at about 13.25 volts. The batteries need to be fairly well charged to start with - i.e., the 5 watt panel will not charge a dead battery or nearly dead battery. But it does a great job of keeping ahead of the natural discharge. Michael
Solar Power
What you need to determine is how much current you will be drawing from the batteries and for how long. For example a radio drawing 500ma, or 1/2 amp for 4 hours would be a 2 amp drain on the battery. The solar panels are rated in watts. Which is P=I*E, or Power(watts) = I(Amps) * E(Voltage). A 50 watt solar panel is typically 17 volts. So 50(watts) = I * 17(Volts), or approx. 3 amps per/hour. A 50 watt solar panel would replace the 2 amps drained in approx. 40 minutes, under full sunlight. If the same radio was on for 24 hrs, 24*1/2amp = 12 amps drain. The drain could be replaced in 4 hours, under full sunlight, with a 50 watt panel. As for charging two batteries, look into a battery isolator which has a + input terminal for the solar panel or other source and two output terminals to the two batteries +. It has internal diodes which will maintain both batteries at the same voltage, yet as the name implies, isolates the batteries from each other. Any auto supply store can get one if they don't carry one in stock. Hope this helps,if not let me know. Sail on.... Terry
What you need to determine is how much current you will be drawing from the batteries and for how long. For example a radio drawing 500ma, or 1/2 amp for 4 hours would be a 2 amp drain on the battery. The solar panels are rated in watts. Which is P=I*E, or Power(watts) = I(Amps) * E(Voltage). A 50 watt solar panel is typically 17 volts. So 50(watts) = I * 17(Volts), or approx. 3 amps per/hour. A 50 watt solar panel would replace the 2 amps drained in approx. 40 minutes, under full sunlight. If the same radio was on for 24 hrs, 24*1/2amp = 12 amps drain. The drain could be replaced in 4 hours, under full sunlight, with a 50 watt panel. As for charging two batteries, look into a battery isolator which has a + input terminal for the solar panel or other source and two output terminals to the two batteries +. It has internal diodes which will maintain both batteries at the same voltage, yet as the name implies, isolates the batteries from each other. Any auto supply store can get one if they don't carry one in stock. Hope this helps,if not let me know. Sail on.... Terry
Something Missing
Before you can decide how much solar, wind or whatever other form of energy you need, you have to determine the total power demands on your boat. For example, a fridge is a big power user. If you have a fridge you want to keep cold it will take much more than a small solar panel to keep up. If only keeping the batteries maintained then you don't need much to do this. Also keep in mind that at best you only get half the day of charging from solar. And most panels are rated under ideal conditions, and the actual output will be much less most of the time.
Before you can decide how much solar, wind or whatever other form of energy you need, you have to determine the total power demands on your boat. For example, a fridge is a big power user. If you have a fridge you want to keep cold it will take much more than a small solar panel to keep up. If only keeping the batteries maintained then you don't need much to do this. Also keep in mind that at best you only get half the day of charging from solar. And most panels are rated under ideal conditions, and the actual output will be much less most of the time.
Total Power consumption
Right, check your owner manuals, usually in the back they show the current used by the product. It is tough to get a completely accurate total in a 24 hour period for some. For example a refrig draws say 5 amps, but only when running. This could be 120 amps for 24 hours when running continous, but not likely. What you do is estimate the run time and current, for all power users in a 24 hour period and then calculate the solar wattage needed to replace the current drain. Sail on.... Terry
Right, check your owner manuals, usually in the back they show the current used by the product. It is tough to get a completely accurate total in a 24 hour period for some. For example a refrig draws say 5 amps, but only when running. This could be 120 amps for 24 hours when running continous, but not likely. What you do is estimate the run time and current, for all power users in a 24 hour period and then calculate the solar wattage needed to replace the current drain. Sail on.... Terry
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