Post by shinester on Apr 11, 2016 10:19:36 GMT 10
If you don't need all of the info, skip to the conclusion 
Car batteries are not the best solution for solar power storage, though they are one solution. For instance, I have a small kit for my 'BOV' [Bug out vehicle] that includes a solar panel, a charge controller and uses the car battery. I can leave the battery in the car [panel on the bonnet] and have a small amount of ongoing power for other gear such as keeping the radio going if it's an emergency or keeping the internal lights for night time or charging phones/radios via the cigarette lighter all without using fuel and in an ongoing fashion.
It's best to understand what the car batter is capable of and what it's not capable of. Firstly a car battery is mostly made for very high currents for a very short amount of time, that is starting your engine. They are made with the thin lead that doesn't hold a lot of charge compared to the same sized package of say AGM or Deep Cycle batteries, though again, it's made for its job and does that well. It's not particularly good in solar applications particularly because they will quickly die if you start draining them heavily. If it's an emergency, you might not care, which is fair enough, it might get you out of trouble. If it's more of an ongoing situation, then how can we use them with a fairly cheap solar panel to keep our phones/torches/radios going?
Smaller car batteries have a capacity of about 45 Amp Hours [AH] when they're new. That is can deliver 1 amps for 45hrs or 10 amps for 4.5hrs. [That's not perfectly correct, though to keep it simple we'll go with it]. This diminishes with age also. We also mentioned above that car batteries don't like being drained heavily as it reduces the life of the battery. Ideally to get the most life we'd only drain 5-10% for the longest life. When you start the car you might be using 400amps, though only for 3-10 seconds or so, so the drain is only about 5-10% which gives us the best life. Draining more?
Well you can drain 70-80% and still get 150-300 cycles. Looking at the battery it might be hard to tell it's charge level, though some cars have volt meters in their dash or you can get a fairly cheap multimeter or condition meter to check also. As you can see, 12.32 Volts is the lower end.
Remember that if you're doing that daily, we're talking about 6-12months when the battery is new. If you start draining it more, you'll get less time. So this means we have 13.5AH of useable power we could use at night, perhaps for lighting or checking the internal radio. At 12V that's [Watts = Volts x Amps] 162WHrs, or we can run 20W of lighting most of the night. Most car bulbs aren't ideal as they're inefficient incandescent bulbs but can be replaced with 1-3W LED bulbs for a few bucks and you'll probably have plenty of light and plenty left over. The bonus is if you leave your car internal light on accidentally over night you'll probably be able to start the car in the morning.
What about charging?
Well if we used all of those 162Whs of power we will need to put at least that back into the battery. Sunlight hours vary with time of the year, where you're located and with weather conditions though here in Vic we get about 2.5hrs during winter and 6.5hrs during summer of usable 'solar radiation'. What this means is that we multiply the solar panel size by the hours for how many 'watt hours' we generate per day. We also have some electrical losses due to inefficiencies and so we can approximate that we'll need about half of the draw we can use in solar panel for night lighting. So if we're planning such an energy use then we'd need a 80W panel to match.
When it comes to my own situation, I'm only planning on running a radio on occasion, perhaps charge a phone and CB radio and a small amount of lighting. So I add up the useage to get an idea of how much power I need.
Charging a Baofeng BF-888S takes 1.5Ah [1500mAh] x 3.7V = 5.6Wh.
Charging a phone 2.5Ah x 3.7V = 9.25Wh
3 hours of lighting 2w = 6Wh
So I'm using a total of about 20.85W, so I could get away with about 11W of solar, assuming I drained them every day, which matches well with my choice of a 20W panel.
As well as the panel we need a charge controller and they go for as little as $10 with the MPPT [more efficient] on ebay. To choose the correct Amp controller, divide the panel size [20W] by the voltage [12V] = 1.7Amp charge controller. I could obviously use one rated to a higher capacity, so 5, 10 etc.
Using power tools?
Firstly you would have to convert the 12V into 240V, which can be done with an inverter. This obviously could be useful for charging cordless tools, or anything that you don't have a 12V input for. Again, you really have to work out how much power you want to draw. You also have to match the power rating of the inverter with the power tool you wish to use. Electric motors have a surge requirement, that is need a start up boost of power to get them going, so you'll be looking for one rated higher than the tool. The battery can handle it [it starts a car motor!] but the inverter also has to be able to handle it. What about run time? Now we'll get into trouble because as we showed above we don't have a lot of storage
162Wh of power would let us run a 1000W tool for only 10 mins and we'll be down to 70% charge.
Conclusions
You can get a small panel 10W+ and connect it to your car battery for running basic LED internal car lights [1-2W] for a few hours and daily charging of your phone/radio [once each]. They have one for $25.50 on ebay that seems to include [I'm waiting on mine to arrive to check] a regulated supply suitable for charging 12V batteries. They may not last too long [6-12months] but it's better than nothing.
Obviously having a purpose built battery is far better.
Car batteries are not the best solution for solar power storage, though they are one solution. For instance, I have a small kit for my 'BOV' [Bug out vehicle] that includes a solar panel, a charge controller and uses the car battery. I can leave the battery in the car [panel on the bonnet] and have a small amount of ongoing power for other gear such as keeping the radio going if it's an emergency or keeping the internal lights for night time or charging phones/radios via the cigarette lighter all without using fuel and in an ongoing fashion.
It's best to understand what the car batter is capable of and what it's not capable of. Firstly a car battery is mostly made for very high currents for a very short amount of time, that is starting your engine. They are made with the thin lead that doesn't hold a lot of charge compared to the same sized package of say AGM or Deep Cycle batteries, though again, it's made for its job and does that well. It's not particularly good in solar applications particularly because they will quickly die if you start draining them heavily. If it's an emergency, you might not care, which is fair enough, it might get you out of trouble. If it's more of an ongoing situation, then how can we use them with a fairly cheap solar panel to keep our phones/torches/radios going?
Smaller car batteries have a capacity of about 45 Amp Hours [AH] when they're new. That is can deliver 1 amps for 45hrs or 10 amps for 4.5hrs. [That's not perfectly correct, though to keep it simple we'll go with it]. This diminishes with age also. We also mentioned above that car batteries don't like being drained heavily as it reduces the life of the battery. Ideally to get the most life we'd only drain 5-10% for the longest life. When you start the car you might be using 400amps, though only for 3-10 seconds or so, so the drain is only about 5-10% which gives us the best life. Draining more?
Well you can drain 70-80% and still get 150-300 cycles. Looking at the battery it might be hard to tell it's charge level, though some cars have volt meters in their dash or you can get a fairly cheap multimeter or condition meter to check also. As you can see, 12.32 Volts is the lower end.
Remember that if you're doing that daily, we're talking about 6-12months when the battery is new. If you start draining it more, you'll get less time. So this means we have 13.5AH of useable power we could use at night, perhaps for lighting or checking the internal radio. At 12V that's [Watts = Volts x Amps] 162WHrs, or we can run 20W of lighting most of the night. Most car bulbs aren't ideal as they're inefficient incandescent bulbs but can be replaced with 1-3W LED bulbs for a few bucks and you'll probably have plenty of light and plenty left over. The bonus is if you leave your car internal light on accidentally over night you'll probably be able to start the car in the morning.
What about charging?
Well if we used all of those 162Whs of power we will need to put at least that back into the battery. Sunlight hours vary with time of the year, where you're located and with weather conditions though here in Vic we get about 2.5hrs during winter and 6.5hrs during summer of usable 'solar radiation'. What this means is that we multiply the solar panel size by the hours for how many 'watt hours' we generate per day. We also have some electrical losses due to inefficiencies and so we can approximate that we'll need about half of the draw we can use in solar panel for night lighting. So if we're planning such an energy use then we'd need a 80W panel to match.
When it comes to my own situation, I'm only planning on running a radio on occasion, perhaps charge a phone and CB radio and a small amount of lighting. So I add up the useage to get an idea of how much power I need.
Charging a Baofeng BF-888S takes 1.5Ah [1500mAh] x 3.7V = 5.6Wh.
Charging a phone 2.5Ah x 3.7V = 9.25Wh
3 hours of lighting 2w = 6Wh
So I'm using a total of about 20.85W, so I could get away with about 11W of solar, assuming I drained them every day, which matches well with my choice of a 20W panel.
As well as the panel we need a charge controller and they go for as little as $10 with the MPPT [more efficient] on ebay. To choose the correct Amp controller, divide the panel size [20W] by the voltage [12V] = 1.7Amp charge controller. I could obviously use one rated to a higher capacity, so 5, 10 etc.
Using power tools?
Firstly you would have to convert the 12V into 240V, which can be done with an inverter. This obviously could be useful for charging cordless tools, or anything that you don't have a 12V input for. Again, you really have to work out how much power you want to draw. You also have to match the power rating of the inverter with the power tool you wish to use. Electric motors have a surge requirement, that is need a start up boost of power to get them going, so you'll be looking for one rated higher than the tool. The battery can handle it [it starts a car motor!] but the inverter also has to be able to handle it. What about run time? Now we'll get into trouble because as we showed above we don't have a lot of storage
162Wh of power would let us run a 1000W tool for only 10 mins and we'll be down to 70% charge.
Conclusions
You can get a small panel 10W+ and connect it to your car battery for running basic LED internal car lights [1-2W] for a few hours and daily charging of your phone/radio [once each]. They have one for $25.50 on ebay that seems to include [I'm waiting on mine to arrive to check] a regulated supply suitable for charging 12V batteries. They may not last too long [6-12months] but it's better than nothing.
Obviously having a purpose built battery is far better.
