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Thread: Question about batteries and solar charging

  1. #1

    Default Question about batteries and solar charging

    I have some AAA solar landscape lights, but I only use them for solar charging the batteries rather than as landscape lights. Also like the idea that they could serve well as lanterns in a power outage.

    The ones I have are only for AAA batteries, but I decided to try an experiment using a AA battery. I wanted to see if I could charge an AA size battery by taping it to the unit (since it won't fit the compartment) and using wires to connect the battery to the contacts, and then placing it in the sun. For some odd reason, the AA battery only charged a very little bit after 9 hours of continuous sunshine. AAA batteries charge up all the way in about 4 hours, so I'm surprised a AA only charges very slightly in 9 hours. And yes, I made absolutely sure the battery was making proper electrical contact. I put the unit in place in the sun, and then held an object over the solar panel to completely block the sun to mimic nighttime. The LED lit up when I did that, ensuring the battery was connected.

    I know I could just go out and buy AA units, but I'm just curious to know why the AA batteries won't charge. It's a NiMH 2000Mah Duracell. 9 hours in the sun should have made more than a tiny difference in the battery's charge.
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  2. #2

    Default Re: Question about batteries and solar charging

    Some solar lights use Nickel Cadmium batteries. If youíre trying to charge a NiMH battery, the voltage for solar charging might be a little low to charge your battery. Even if it takes a NiMH AAA, a 600 mAh AAA will charge 3-4 times faster than a 2000 mAh AA. That AA could take 4 days to charge. Most solar lights take at least 8 hours to charge the battery they come with.

  3. #3

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Hooked on Fenix View Post
    Some solar lights use Nickel Cadmium batteries. If youíre trying to charge a NiMH battery, the voltage for solar charging might be a little low to charge your battery. Even if it takes a NiMH AAA, a 600 mAh AAA will charge 3-4 times faster than a 2000 mAh AA. That AA could take 4 days to charge. Most solar lights take at least 8 hours to charge the battery they come with.
    The AAA it came with is Ni-MH, same as the AA I tried.
    But the solar lights I've seen that use a AA battery look exactly the same as the AAA units, with the same size solar panel. If they take 4 days to charge, they wouldn't work any better than one with a AAA. Aren't the AA lights expected to fully charge?
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  4. #4

    Default Re: Question about batteries and solar charging

    Youíre assuming that the AAs they put in solar lights have a higher capacity than the AAAs. Most use AAs with 500-600 mAh. Some of the more expensive ones use a 2000 mAh battery. If youíre trying to use a higher capacity AA in a light that uses a AAA, itís probably designed to charge that lower capacity AAA in a day. Take the capacity of the AA you want to charge and divide it by the capacity of that AAA it came with and multiply by 8 hours and youíll probably get an idea of how long it will take to charge.

  5. #5

    Default Re: Question about batteries and solar charging

    Get a proper solar panel + adjustable controller

  6. #6

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Hooked on Fenix View Post
    Youíre assuming that the AAs they put in solar lights have a higher capacity than the AAAs. Most use AAs with 500-600 mAh. Some of the more expensive ones use a 2000 mAh battery. If youíre trying to use a higher capacity AA in a light that uses a AAA, itís probably designed to charge that lower capacity AAA in a day. Take the capacity of the AA you want to charge and divide it by the capacity of that AAA it came with and multiply by 8 hours and youíll probably get an idea of how long it will take to charge.
    I've seen AA's that are made for solar lights and have capacities of 2,000Mah that are made for solar lights on Amazon, but I guess those must be made for solar lights that have a bigger solar panel.

    I just figured that my AA would charge more than it did. Maybe not all the way, but more than just a tiny bit. I attached an image of my old battery tester to show you exactly the difference made when I tried charging the AA battery. When I started out, the needle went up to the right edge of "replace" (the red zone). After 9 hours of solar charging, the needle only went up to the left edge of "good". So it just crossed that tiny little in-between area.
    h
    https://imgur.com/a/f8MMz6O

    Well, I guess all I could do is give you a link to the image since it won't actually appear. It's a pic of my tester to show you what I'm talking about.

    tps://imgur.com/yMlPbFd


    Last edited by LEDrock; 06-14-2021 at 12:09 PM.
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  7. #7

    Default Re: Question about batteries and solar charging

    Remember, the solar light you tried charging a AA with was made for a AAA. AAAs only go up to 900 mAh and some are only 300 mAh. Usually the capacity is written on the cell. Expect your light to charge to that capacity in 8-12 hours. There are no 2000 mAh AAAs in existence so there is no way that light will charge a high capacity AA in anything close to a day. If the light is 20 lumens or higher, it might have a 2000 mAh AA in it with a larger solar panel. Best to get a real solar charger if you want to charge AAs.

  8. #8

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Hooked on Fenix View Post
    Remember, the solar light you tried charging a AA with was made for a AAA. AAAs only go up to 900 mAh and some are only 300 mAh. Usually the capacity is written on the cell. Expect your light to charge to that capacity in 8-12 hours. There are no 2000 mAh AAAs in existence so there is no way that light will charge a high capacity AA in anything close to a day. If the light is 20 lumens or higher, it might have a 2000 mAh AA in it with a larger solar panel. Best to get a real solar charger if you want to charge AAs.
    The 2,000 Mah battery I was referring to is the AA battery I was using. I do have AAA batteries that are 600 Mah, and they get quite a charge boost after just 1 hour. That's why I was surprised to see so little difference in the AA battery (a little over 3 times the capacity) after being in the sun 9 times as long.
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  9. #9
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    The 2,000 Mah battery I was referring to is the AA battery I was using. I do have AAA batteries that are 600 Mah, and they get quite a charge boost after just 1 hour. That's why I was surprised to see so little difference in the AA battery (a little over 3 times the capacity) after being in the sun 9 times as long.
    Without seeing this solar setup I'm guessing it has a rather small solar cell that likely is rated at about 60ma output. It is also possible the 600mah battery you have is way overrated in capacity either a cheap chinese cell or damaged with very low capacity it could seem it get a bigger charge than 9 hours at 60ma or about 540ma with losses is about 1/4 of the capacity of a 2000mah battery.
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  10. #10

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    Without seeing this solar setup I'm guessing it has a rather small solar cell that likely is rated at about 60ma output. It is also possible the 600mah battery you have is way overrated in capacity either a cheap chinese cell or damaged with very low capacity it could seem it get a bigger charge than 9 hours at 60ma or about 540ma with losses is about 1/4 of the capacity of a 2000mah battery.
    I hadn't considered that the 600mah batteries aren't really what they're labeled as. That could certainly affect it. But they do seem significantly better than the 300mah batteries that originally came in the lights.
    I'd take a picture of the lights I have and post it, but that didn't work very well when I took one of my charger and tried posting it in post #6. But here's an Amazon ad that has ones that has a light/solar module similar to mine. https://www.amazon.com/AlJoLife-Deco...3802086&sr=8-4

    We're talking the lower end of the scale here.
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  11. #11
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    I hadn't considered that the 600mah batteries aren't really what they're labeled as. That could certainly affect it. But they do seem significantly better than the 300mah batteries that originally came in the lights.
    I'd take a picture of the lights I have and post it, but that didn't work very well when I took one of my charger and tried posting it in post #6. But here's an Amazon ad that has ones that has a light/solar module similar to mine. https://www.amazon.com/AlJoLife-Deco...3802086&sr=8-4

    We're talking the lower end of the scale here.
    The stats on these are rather pitiful. 25ma @ 2V and runtime of 8 hours at 5 lumens.... that is like 40 lumens for 1 hour which doesn't take much power at all to accomplish these day If your setup is like that then the charging rate is LESS than 60ma more along the lines of about 35 ma which reduces the capacity requirement even more such that 9 hours would not even equal 400mah or 20% of a AA 2000mah battery.
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  12. #12
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    Without seeing this solar setup I'm guessing it has a rather small solar cell that likely is rated at about 60ma output. It is also possible the 600mah battery you have is way overrated in capacity either a cheap chinese cell or damaged with very low capacity it could seem it get a bigger charge than 9 hours at 60ma or about 540ma with losses is about 1/4 of the capacity of a 2000mah battery.
    Funny you should mention that number.

    Here's an estimate I made for maximum charging rate for a small solar light (spotlight from Dollar Tree), not confirmed yet by measurement.

    Light uses approx. 3x3cm (0.0009 sq. metre) amorphous panel. Maximum sunlight is 1000 watts per square metre, that being noon on a sunny day so panel would see 0.9W. Amorphous is about 8% efficient, so 0.072W is available. At 1.25v average charging voltage that gives 57.6mA charging current. Sun angle changes during the day, average (RMS) factor would be 0.707, so average current about 41mA. For an 8-hour charging day that's 326mAh which seems optimistic, assumes sunny days with no clouds or other obstruction. In terms of 2000mAh cell it would take about a week to charge.

    The little $1.50 light had a 100mAh AAA cell which I replaced with 200mAh. Statistically, anything higher is probably no benefit.

    Dave

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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post

    I just figured that my AA would charge more than it did. Maybe not all the way, but more than just a tiny bit. I attached an image of my old battery tester to show you exactly the difference made when I tried charging the AA battery. When I started out, the needle went up to the right edge of "replace" (the red zone). After 9 hours of solar charging, the needle only went up to the left edge of "good". So it just crossed that tiny little in-between area.
    h


    tps://imgur.com/yMlPbF

    Sorry for some reason I can't see the image.

    If you have or can obtain a digital multi-meter (DMM) you could do some simple measurements.

    If your battery meter is indicating voltage, with NiCd and NiMH there is not as great of voltage range as with alkaline or zinc-carbon cells; especially with such slow charge rate. NiMH below 1.2v is essentially dead, and fully-charged not much above 1.3v.

    Dave

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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by john61ct View Post
    Get a proper solar panel + adjustable controller
    I think I see the OP's point, it's cheap, an experiment, and the lights are "doing something" more than perhaps sitting in their packaging in the shade.

    Dave

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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Dave_H View Post
    Funny you should mention that number.

    Here's an estimate I made for maximum charging rate for a small solar light (spotlight from Dollar Tree), not confirmed yet by measurement.

    Light uses approx. 3x3cm (0.0009 sq. metre) amorphous panel. Maximum sunlight is 1000 watts per square metre, that being noon on a sunny day so panel would see 0.9W. Amorphous is about 8% efficient, so 0.072W is available. At 1.25v average charging voltage that gives 57.6mA charging current. Sun angle changes during the day, average (RMS) factor would be 0.707, so average current about 41mA. For an 8-hour charging day that's 326mAh which seems optimistic, assumes sunny days with no clouds or other obstruction. In terms of 2000mAh cell it would take about a week to charge.

    The little $1.50 light had a 100mAh AAA cell which I replaced with 200mAh. Statistically, anything higher is probably no benefit.

    Dave
    I agree, the only benefit is if it has a light sensor that shuts it off and you charge a large battery up and when you have an overcast day it can use the extra capacity to power the light but it won't be restored by solar charging.
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  16. #16

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Dave_H View Post
    Sorry for some reason I can't see the image.

    If you have or can obtain a digital multi-meter (DMM) you could do some simple measurements.

    If your battery meter is indicating voltage, with NiCd and NiMH there is not as great of voltage range as with alkaline or zinc-carbon cells; especially with such slow charge rate. NiMH below 1.2v is essentially dead, and fully-charged not much above 1.3v.

    Dave
    Here's that link to the image of my charger. If it doesn't work by clicking, just copy/paste url into a browser.

    https://imgur.com/a/f8MMz6O
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  17. #17

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Dave_H View Post
    Funny you should mention that number.

    Here's an estimate I made for maximum charging rate for a small solar light (spotlight from Dollar Tree), not confirmed yet by measurement.

    Light uses approx. 3x3cm (0.0009 sq. metre) amorphous panel. Maximum sunlight is 1000 watts per square metre, that being noon on a sunny day so panel would see 0.9W. Amorphous is about 8% efficient, so 0.072W is available. At 1.25v average charging voltage that gives 57.6mA charging current. Sun angle changes during the day, average (RMS) factor would be 0.707, so average current about 41mA. For an 8-hour charging day that's 326mAh which seems optimistic, assumes sunny days with no clouds or other obstruction. In terms of 2000mAh cell it would take about a week to charge.

    The little $1.50 light had a 100mAh AAA cell which I replaced with 200mAh. Statistically, anything higher is probably no benefit.

    Dave
    I'm surprised the battery your light had was so low in capacity. I didn't know 100Mah AAA's existed. My lights ($1 at Menards before 100% rebate offer) came with 300Mah battery. I did a runtime test with it and found it runs the light for 5.5 hours. I also have 600Mah batteries that I assume would run twice as long.
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    Default Re: Question about batteries and solar charging

    Maybe they are 1/3AAA nicads in a AAA case.
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  19. #19

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    Maybe they are 1/3AAA nicads in a AAA case.
    The manufacturer must be pretty desperate to make something like that.
    Anything to save on cost.
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    The manufacturer must be pretty desperate to make something like that.
    Anything to save on cost.
    You would be surprised how much the Chinese do to try and save a fraction of a cent on manufacturing costs. There have been fake batteries made before with other tiny batteries inside of a bigger cell. Even Rayovac and others have played the game by putting a Sub C battery inside a rechargeable D cell at one time.
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  21. #21

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    You would be surprised how much the Chinese do to try and save a fraction of a cent on manufacturing costs. There have been fake batteries made before with other tiny batteries inside of a bigger cell. Even Rayovac and others have played the game by putting a Sub C battery inside a rechargeable D cell at one time.
    Here's a slightly different question that's related to the first. What do you think of solar panels bought from Amazon that are simply a panel with 2 wires coming out of it that would be connected directly to a battery? Is that all that's needed to charge a battery? Does the panel's voltage factor into it?

    Here's one I found. What do you think? https://www.amazon.com/Alligator-Pol...942504&sr=8-13

    Or even something like this? https://www.amazon.com/AMX3d-Micro-M...&rps=1&sr=8-56
    Last edited by LEDrock; 06-17-2021 at 11:52 AM.
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    I'm surprised the battery your light had was so low in capacity. I didn't know 100Mah AAA's existed. My lights ($1 at Menards before 100% rebate offer) came with 300Mah battery. I did a runtime test with it and found it runs the light for 5.5 hours. I also have 600Mah batteries that I assume would run twice as long.

    Keep in mind that this is a dollar-store product and cost needs to be kept down by whatever means. Some solar lights come with cells of higher capacity than the charger can keep up with in some conditions. Not bad, just wasted capacity and higher cost. With NiMH it's better to not reach capacity and overcharge anyway.

    I have found solar NiCd AA's as low as 150mAh, and a variety of NiCd/NiMH sub-cells including 2/3AA, 2/3AAA and even 1/3AAA (200mAh). It is all about keeping cost and size down.

    My cheap spotlight was running most of the night with good day of sunlight (6-7 hours). Run time depends on the LED brightness/current. I assumed cell could charge to 100mAh in a day under good conditions. Cell capacity was bumped, but I also increased LED brightness by changing an inductor. Just an aside, not important when just charging cells as OP does.

    Dave

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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    I agree, the only benefit is if it has a light sensor that shuts it off and you charge a large battery up and when you have an overcast day it can use the extra capacity to power the light but it won't be restored by solar charging.
    My estimate doesn't account for efficiency lost in the charging circuit itself. For example many solar charge IC datasheets show connection between solar panel and cell through a diode (some are direct). Schottky diode drop should be less than 0.5v but for 1.25v cell is substantial.

    Also unknown how well the solar panel and cell are matched for optimum transfer i.e. at maximum power point, hopefully somewhere close.

    Dave

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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    Here's a slightly different question that's related to the first. What do you think of solar panels bought from Amazon that are simply a panel with 2 wires coming out of it? Is that all that's needed to charge a battery? Does the panel's voltage factor into it?

    Here's one I found. What do you think? https://www.amazon.com/Alligator-Pol...942504&sr=8-13

    Or even something like this? https://www.amazon.com/AMX3d-Micro-M...&rps=1&sr=8-56
    Consider panels like cells in a battery. If a panel has a single "cell" then it is the voltage of that cell alone. You can buy batteries with multiple cells like lead acid batteries and you can buy packs of cells wired together to get higher current output and/or higher voltage and the similar applies to solar cells. While I'm not anywhere near an expert on solar tech, it is obvious that higher voltage panels have multiple cells in series and larger current output panels have either larger individual cells or many paralleled and put the arrays in series to get required voltage. From what I have seen panels can put out a lot higher voltage than they are related and under a load they "sag" to lower voltages and the sunlight on them can vary widely greatly affecting their output. Matching solar cells to loads is likely a challenge if the panel has overall more power (in wattage) than the device can handle which could cause the voltage to float higher than the device is made for and cause damage. This is why they have some sort of regulation circuitry on panels a controller or something like that to limit the voltage to a set level. Most devices are designed to take a certain voltage and as long as that voltage isn't exceeded it can be put on ANY source from adequate amps to 1000 amps even with no issue as the device will only consume what it needs if it draws half an amp then it will draw that much and the other potention 999.5A capability is unneeded. There are ways to get around issues of solar output of cells widely varying due to sun output and weather and daytime and shade and clouds etc one is by charging a big battery and using that to charge and run smaller items it can be as a buffer but may need to be disconnected from solar to use it. Another way is to match the output of the solar cell with the load such that it cannot exceed the load regardless of the light output.
    2 wires is all you need from a solar cell to use access its power, but matching the cell to your device is where it can be tricky.
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Dave_H View Post
    My estimate doesn't account for efficiency lost in the charging circuit itself. For example many solar charge IC datasheets show connection between solar panel and cell through a diode (some are direct). Schottky diode drop should be less than 0.5v but for 1.25v cell is substantial.

    Also unknown how well the solar panel and cell are matched for optimum transfer i.e. at maximum power point, hopefully somewhere close.

    Dave
    I doubt they engineer them with much care for efficiency rather than focus on cheap cost and something that works well enough for a long enough time that people will buy them to "try them out" and maybe buy others and 6 months later when they start to die the stores will run out of them or there will be other folks still buying them for the first time.
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    Here's a slightly different question that's related to the first. What do you think of solar panels bought from Amazon that are simply a panel with 2 wires coming out of it that would be connected directly to a battery? Is that all that's needed to charge a battery? Does the panel's voltage factor into it?

    Here's one I found. What do you think? https://www.amazon.com/Alligator-Pol...942504&sr=8-13

    Or even something like this? https://www.amazon.com/AMX3d-Micro-M...&rps=1&sr=8-56
    Yes you could use a stand-alone solar panel (and a much larger one) but requires at least minimal interface circuit to the cell(s) being charged. You need to limit current and not overcharge. Also a blocking diode prevents leakage back into the solar panel during darkness.

    Charging a single cell with a poly-crystaline panel requires at least four solar cells in series. You see this on some solar garden lights; or multiple banks of four in parallel for higher current.

    First item seems to have two banks of three cells, which is a bit short for a single cell. A little pricey, otherwise would have been OK. Keep in mind 400mA is probably peak, expect lower average.

    Second item, 12v panel is way high for single cell charging. Appears to be two 6v banks in series. You could drop the excess voltage but it would be very inefficient. Some sort of step-down converter would be required. Depends how far you want to go with this.

    Dave
    Last edited by Dave_H; 06-17-2021 at 12:29 PM.

  27. #27

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    Consider panels like cells in a battery. If a panel has a single "cell" then it is the voltage of that cell alone. You can buy batteries with multiple cells like lead acid batteries and you can buy packs of cells wired together to get higher current output and/or higher voltage and the similar applies to solar cells. While I'm not anywhere near an expert on solar tech, it is obvious that higher voltage panels have multiple cells in series and larger current output panels have either larger individual cells or many paralleled and put the arrays in series to get required voltage. From what I have seen panels can put out a lot higher voltage than they are related and under a load they "sag" to lower voltages and the sunlight on them can vary widely greatly affecting their output. Matching solar cells to loads is likely a challenge if the panel has overall more power (in wattage) than the device can handle which could cause the voltage to float higher than the device is made for and cause damage. This is why they have some sort of regulation circuitry on panels a controller or something like that to limit the voltage to a set level. Most devices are designed to take a certain voltage and as long as that voltage isn't exceeded it can be put on ANY source from adequate amps to 1000 amps even with no issue as the device will only consume what it needs if it draws half an amp then it will draw that much and the other potention 999.5A capability is unneeded. There are ways to get around issues of solar output of cells widely varying due to sun output and weather and daytime and shade and clouds etc one is by charging a big battery and using that to charge and run smaller items it can be as a buffer but may need to be disconnected from solar to use it. Another way is to match the output of the solar cell with the load such that it cannot exceed the load regardless of the light output.
    2 wires is all you need from a solar cell to use access its power, but matching the cell to your device is where it can be tricky.
    So let's say all I wanted to do was connect a solar panel directly to a AA battery (1.2V NiMH with 2000Mah capacity) to charge it fully in 10 hours. What would the voltage and output of the solar panel have to be? My guess is a 1.2V panel that puts out 200 MA. Would I be correct?

    Of course, this doesn't involve any converters or controllers. It would just be a matter of keeping an eye on it and testing the battery every so often to make sure it's not about to overcharge. With practice, I could figure out how long to leave it in the sun.
    Last edited by LEDrock; 06-17-2021 at 12:39 PM.
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  28. #28
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Dave_H View Post
    Yes you could use a stand-alone solar panel (and a much larger one) but requires at least minimal interface circuit to the cell(s) being charged. You need to limit current and not overcharge. Also a blocking diode prevents leakage back into the solar panel during darkness.

    Charging a single cell with a poly-crystaline panel requires at least four solar cells in series. You see this on some solar garden lights; or multiple banks of four in parallel for higher current.

    First item seems to have two banks of three cells, which is a bit short for a single cell. A little pricey, otherwise would have been OK. Keep in mind 400mA is probably peak, expect lower average.

    Second item, 12v panel is way high for single cell charging. Appears to be two parallel banks of 24 cells in series. You could drop the excess voltage but it would be very inefficient. Some sort of step-down converter would be required. Depends how far you want to go with this.

    Dave
    12v panels can charge 12v larger lead acid batteries directly as long as the continual charging rate is not over trickle charging them or you have a controller to shut off charging and you can then use the battery to charge other devices. This is a common method used. USB 5V charger setups are out there that the only issue with them I know of (and I don't know all issues) is the current output may drop too low to charge some devices at all.
    I think you are getting deep into solar setups far beyond my limited knowledge and unless someone who is more experienced than I am steps in I won't be able to give you much info. I've not delved into solar other than reading about it and a knowledge of electronics in general of some circuitry used in it. I have little to know direct knowledge of solar controllers and how they work so setting up something more than a throwaway solar garden light is beyond my expertise at this time. They do make buck converters to step down voltage but for purposes of charging if the cell has the ability to put out more than what is a safe charging rate and can overcharge the cell (doesn't have a shutoff) then it can damage your battery over time.
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  29. #29
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: Question about batteries and solar charging

    Quote Originally Posted by LEDrock View Post
    So let's say all I wanted to do was connect a solar panel directly to a AA battery (1.2V NiMH with 2000Mah capacity) to charge it fully in 10 hours. What would the voltage and output of the solar panel have to be? My guess is a 1.2V panel that puts out 200 MA. Would I be correct?
    Nowhere near that simple long term. Yes you could get a setup to charge the battery fully like that but there is many considerations to solar charging like not having continual full output from the cell due to moving sun and weather/clouds, loss in charging due to heating the cell up, overcharging damage to the cell if if you don't stop charging when full also. Over time you could fully charge the battery but it could be slowly damaged and lose capacity such that normal amount of good cycle use would suffer. In order to charge it properly and not harm the battery in doing so you likely will need a larger solar cell and higher voltage to incorporate charging circuitry and also account for a more average sun output as solar cells are labeled for max output a 200ma output cell over 10 hours may only put 1200mah into the battery due to losses and not having peak sun on it. You charge it the next day for 10 hours and only 6 hours are needed for it to reach full and for 4 hours it literally cooks the cell overcharging it and damaging it unless you have some way to detect it is full (a smart charger) you would have to estimate how much charge it got and limit overcharging or undercharge it some.
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  30. #30

    Default Re: Question about batteries and solar charging

    Quote Originally Posted by Lynx_Arc View Post
    Nowhere near that simple long term. Yes you could get a setup to charge the battery fully like that but there is many considerations to solar charging like not having continual full output from the cell due to moving sun and weather/clouds, loss in charging due to heating the cell up, overcharging damage to the cell if if you don't stop charging when full also. Over time you could fully charge the battery but it could be slowly damaged and lose capacity such that normal amount of good cycle use would suffer. In order to charge it properly and not harm the battery in doing so you likely will need a larger solar cell and higher voltage to incorporate charging circuitry and also account for a more average sun output as solar cells are labeled for max output a 200ma output cell over 10 hours may only put 1200mah into the battery due to losses and not having peak sun on it. You charge it the next day for 10 hours and only 6 hours are needed for it to reach full and for 4 hours it literally cooks the cell overcharging it and damaging it unless you have some way to detect it is full (a smart charger) you would have to estimate how much charge it got and limit overcharging or undercharge it some.
    Thanks! I guess it's more complicated that it seems. I'm not much of a techie like I wish I was. I'll probably just stick with doing things the conventional way instead of buying or scavenging parts and trying to construct my own. Those solar chargers that have an attached 10,000Mah battery (often bigger) sound good, but then that doesn't charge conventional batteries. They're built to charge up smartphones and tablets. They have AA and AAA solar chargers, but they cost just as much and have low reviews. That's why I was thinking of just making my own.
    Minimag with niteize LED (2), River Rock 2AAA (2), River Rock 2AA, Brinkmann 3AAA LED headlamp, ROV Roughneck 2D, Inova keychain LED, Performance Tool 3AAA.

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