Question about batteries and solar charging

LEDrock

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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.
 

Hooked on Fenix

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Some solar lights use Nickel Cadmium batteries. If you’re 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.
 

LEDrock

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Some solar lights use Nickel Cadmium batteries. If you’re 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?
 

Hooked on Fenix

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You’re 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 you’re trying to use a higher capacity AA in a light that uses a AAA, it’s 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 you’ll probably get an idea of how long it will take to charge.
 

LEDrock

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You’re 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 you’re trying to use a higher capacity AA in a light that uses a AAA, it’s 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 you’ll 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


yMlPbFd
 
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Hooked on Fenix

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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.
 

LEDrock

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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.
 

Lynx_Arc

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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.
 

LEDrock

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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/dp/B08T1RBQND/?tag=cpf0b6-20

We're talking the lower end of the scale here.
 

Lynx_Arc

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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/dp/B08T1RBQND/?tag=cpf0b6-20

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.
 

Dave_H

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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
 

Dave_H

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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

yMlPbFd

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
 

Lynx_Arc

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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.
 

LEDrock

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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
 

LEDrock

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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.
 

Lynx_Arc

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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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