is it ok to connect a solar panel straight to a battery to charge?
do i just connect the positive to positive and negative to negative?
also, lets say the battery is a 12V DC battery but has been discharged down to 6V. If the solar panel is getting 8V then its ok to connect them?
it is okay provided a couple of things. But if it were me, I would put a diode in the line. A diode is an electrical check valve, allowing current to flow in one direction, but not the other. This will allow the panel to charge the battery, but not let the battery discharge into the panel at night. Most panels today come with diodes already installed in the junction box. We have ours hooked up this way.
First, the voltage does not matter, as long as the panel voltage, or "Open Circuit Voltage," is higher than the battery's full charge voltage. This is why most panels today are wired for 18 volts, so they can charge a 12 volt battery. The panel voltage will simply sag to match the battery's charging curve voltage during the daytime. Second, if the panels max amps, or, "Short Circuit Current," rating is below 2% of the battery's amp hour capacity, then the panel will never overcharge the battery. You said your panel was putting out 8 volts? This is unusual, and I'm wondering if you checked the voltage while the battery was charging, or if you used the wrong contacts in the panels junction box for your voltage reading. A panel in direct sun without anything hooked to it should put out about 17 or 18 volts, unless it is wired for some other nominal voltage, other than 12. If you were charging a battery that was previously reading 6 volts, then 8 volts might be about right during the first phase of the charge, it will climb to 15 or so when finishing. Our system uses two 50 watt panels, with a max amperage of 6 amps, to charge 4 golf cart batteries, which are wired for an amp hour capacity of 440 AH, so we are well within the 2% window, and we do not use a charge controller. Our home is completely powered by the wind and sun, has been for 11 years now, but our little 12 volt system is still working along side of that, running some small lights and DC outlets in the home for small electronics. Just make sure if you do a direct hook up, that you keep the batteries watered at least once a month with distilled water, they will go through some electrolyte this way.
Do not confuse a charge controller with a voltage controller. One is for charging batteries with a high current array, the other is used to send solar power directly to a device, like a water pump. There is a great discussion of all of this in Richard Perez's book, "The Complete Battery Book," look for it in your library. Richard happens to be the founding editor of Home Power Magazine, a good periodical on solar and wind power. I will put some ther sources below for you too. Be careful of what you read online about renewable energy, one thing I have learned over the years working on our home and teaching solar power courses at the local schools, is that there is a vast acreage of misinformation out there. Plenty of people are always willing to offer their advice on solar and wind, even though they have never laid a hand on a panel or wind turbine. I've had my hands on plenty of them, and they work fine once you understand them. Good luck Jt, and take care, Rudydoo
do i just connect the positive to positive and negative to negative?
also, lets say the battery is a 12V DC battery but has been discharged down to 6V. If the solar panel is getting 8V then its ok to connect them?
it is okay provided a couple of things. But if it were me, I would put a diode in the line. A diode is an electrical check valve, allowing current to flow in one direction, but not the other. This will allow the panel to charge the battery, but not let the battery discharge into the panel at night. Most panels today come with diodes already installed in the junction box. We have ours hooked up this way.
First, the voltage does not matter, as long as the panel voltage, or "Open Circuit Voltage," is higher than the battery's full charge voltage. This is why most panels today are wired for 18 volts, so they can charge a 12 volt battery. The panel voltage will simply sag to match the battery's charging curve voltage during the daytime. Second, if the panels max amps, or, "Short Circuit Current," rating is below 2% of the battery's amp hour capacity, then the panel will never overcharge the battery. You said your panel was putting out 8 volts? This is unusual, and I'm wondering if you checked the voltage while the battery was charging, or if you used the wrong contacts in the panels junction box for your voltage reading. A panel in direct sun without anything hooked to it should put out about 17 or 18 volts, unless it is wired for some other nominal voltage, other than 12. If you were charging a battery that was previously reading 6 volts, then 8 volts might be about right during the first phase of the charge, it will climb to 15 or so when finishing. Our system uses two 50 watt panels, with a max amperage of 6 amps, to charge 4 golf cart batteries, which are wired for an amp hour capacity of 440 AH, so we are well within the 2% window, and we do not use a charge controller. Our home is completely powered by the wind and sun, has been for 11 years now, but our little 12 volt system is still working along side of that, running some small lights and DC outlets in the home for small electronics. Just make sure if you do a direct hook up, that you keep the batteries watered at least once a month with distilled water, they will go through some electrolyte this way.
Do not confuse a charge controller with a voltage controller. One is for charging batteries with a high current array, the other is used to send solar power directly to a device, like a water pump. There is a great discussion of all of this in Richard Perez's book, "The Complete Battery Book," look for it in your library. Richard happens to be the founding editor of Home Power Magazine, a good periodical on solar and wind power. I will put some ther sources below for you too. Be careful of what you read online about renewable energy, one thing I have learned over the years working on our home and teaching solar power courses at the local schools, is that there is a vast acreage of misinformation out there. Plenty of people are always willing to offer their advice on solar and wind, even though they have never laid a hand on a panel or wind turbine. I've had my hands on plenty of them, and they work fine once you understand them. Good luck Jt, and take care, Rudydoo
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