Cheap ebay solar LED lights with li-ion 18650 batteries.

Big Easy

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I have a bunch of cheap outdoor ebay solar rechargeable LED lights with li-ion 18650 3.7v batteries.

If I replaced the 3.7v li-ion batteries with 3.2v LiFePO4 18650ifr batteries, would it work just the same? Would the solar panels and circuitry that are designed to charge 3.7v batteries overcharge the 3.2v Lifepo4 batteries (I assume yes, but the lifepo4 batteries are more stable of overcharge, right)? Will the lights be the same brightness with the .5v lower voltage?

Also the li-ion batteries are 2000mah, the LiFePO4 batteries are 1500mah. I think that means the solar lights won't stay lit as long of time through the night?

Last thing, can I use the lifepo4 18650ifr 3.2v batteries in my 18650 li-ion 3.7v flashlights if I use a lifepo4 specific battery charger? -what will the result be --short charge life, dimmer light?

Thanks for any replies.
 
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Dave_H

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I definitely recommend against putting LiFePO4 cell into any solar device (or anything which charges) meant for regular Li-ion. The former will be overcharged and ultimately damaged. I am not sure what are safety risks, but in any case the outcome will not be good.

You can certainly run LiFePO4 cells in flashlights meant for Li-ion, but you may get lower brightness if the drive is linear (as many are). Not sure if some lights will have problem with low-voltage shutdown. In any case, charger should be specific for LiFePO4 which terminates around 3.63v compared to 4.1v to 4.2v . Runtime might be shorter but LiFePO4 if treated right can handle a lot of cycles, up to thousands.

Dave
 

Big Easy

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I definitely recommend against putting LiFePO4 cell into any solar device (or anything which charges) meant for regular Li-ion. The former will be overcharged and ultimately damaged. I am not sure what are safety risks, but in any case the outcome will not be good.

You can certainly run LiFePO4 cells in flashlights meant for Li-ion, but you may get lower brightness if the drive is linear (as many are). Not sure if some lights will have problem with low-voltage shutdown. In any case, charger should be specific for LiFePO4 which terminates around 3.63v compared to 4.1v to 4.2v . Runtime might be shorter but LiFePO4 if treated right can handle a lot of cycles, up to thousands.

Dave
Hey Dave, thanks for the reply.
I'm not worried about damaging the light or battery, I'm only worried about them catching fire. I've had the solar lights for several years, and the original Li-ion 18650s are starting to fail. I figured since Lifepo4 batteries don't have the same danger of catching on fire or exploding, that replacing with the IFR 18650s might be good.
The reason for my concern of the 18650 Li-ion is the telling of so many of these type of solar lights catching fire. I'll probably just take them down, charge the batteries with charger and use them in the event of power outage.

Here's a light and from the same company (Litom) that I have.

Below is a review of this company (Litom) and the light caught on fire. Not good :(

Thanks again for the post, Dave.
 
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ikanode

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See the article at: https://www.powerstream.com/LLLF.htm

According to it, LiFePO4 can take a max of 4.2v (with shorter life). "Continuous charging over 4.3V would either damage the battery performance, such as cycle life, or result in fire or explosion."

If the fires occur more often than extremely-rarely, the lights are probably over-charging the Li-Ions (or maybe they used garbage cells). I'd either throw them away, or experiment with them. Move one away from buildings and check the voltage in the afternoon of a day of full sun with both Li-ion and then LiFePO4. See what the charging circuit is doing--then decide on what to do with them.
 

Big Easy

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See the article at: https://www.powerstream.com/LLLF.htm

According to it, LiFePO4 can take a max of 4.2v (with shorter life). "Continuous charging over 4.3V would either damage the battery performance, such as cycle life, or result in fire or explosion."

If the fires occur more often than extremely-rarely, the lights are probably over-charging the Li-Ions (or maybe they used garbage cells). I'd either throw them away, or experiment with them. Move one away from buildings and check the voltage in the afternoon of a day of full sun with both Li-ion and then LiFePO4. See what the charging circuit is doing--then decide on what to do with them.
Hi, ikanode
I think the sentence you quoted telling about fire or explosion is for ILiCoO2, not LiFePO4. I've done some more research and have seen some results of overcharging lifepo4 batteries and am confident they won't catch fire or explode. It can ruin the batteries though.

I don't have the lifeo4 batteries yet (waiting to come in mail), but have done some testing. The lights solar panel and circuitry, without battery in, in direct sun are putting out 5v tested at battery connections, but I think the battery in must act as a buffer to lower that hight voltage?

I'm going to do as you said and test them with in lifepo4 batteries in when the batteries come, and will report the results.

Thank you for your reply.
 
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eff

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- would it work just the same?
Most lights running 18650 li-ion, have a circuitry that checks the battery voltage. They will automatically shut off (around 3.2v-3.3v) to prevent cell damage.
No way to know if the 18650 LifePo will work in the ebay lights. If they do a voltage check, they might stop running, way before emptying the batteries

- Would the solar panels and circuitry that are designed to charge 3.7v batteries overcharge the 3.2v Lifepo4 batteries
Chargers working with solar panels, are configured to work with lithium cells with a 4.2v - 3.3v voltage range.
Your 18650 LifePo voltage range does not match, and there is a high risk of overcharging the cells.

For safety reasons, you'd better off chargeing the LifePo with a specific charger that has a max voltage charge of 3.2v instead of 4.2v.
LifePo chargers are usually taking their power from the mains plugs Not sure they can run with a solar panel (not enough power to run the charger)
 
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Big Easy

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Most lights running 18650 li-ion, have a circuitry that checks the battery voltage. They will automatically shut off (around 3.2v-3.3v) to prevent cell damage.
No way to know if the 18650 LifePo will work in the ebay lights. If they do a voltage check, they might stop running, way before emptying the batteries
That's a good point, that I didn';t consider. I'm pretty sure that even if they will work, they won't be of much use with the lifepo4 batteries.
 

Big Easy

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I got the LiFePO4 batteries and have been doing some testing.

Charging the two batteries (Lithium Ion and LiFePO4) in identical lithium Ion solar lights, in full sun all day with me rotating them for most sun, the lights getting around 9hrs of charging sun (something they'll never see just mounted on the wall, getting a max of 3hrs sun a day). The result is even though the lithium Ion solar lights/chargers put out 5v without a battery (tested at battery compartment), with battery in, the battery seems to buffer it, and will only allowed the LiFePO4 batteries to charge to 3.25v (they have a max charge of 3.65v).

After charging I function tested; when I set them to medium light/constant, the lights with LiFePO4 batteries are dimmer than the Lithium Ion batteries for approx the first hour, then the same (not measured brightness, just what I can tell by shining around shaded room) brightness after. They both ran the same 4.5hrs, both turning off within 2 minutes of each other from discharge (the Lithium Ion won by 2 minutes).
The LiFePO4 batteries are brand new and are 1.8ah, the Lithium Ion batteries are used and are 2.0ah. I'll test again with new Lithium Ion batteries next time, but I only have new Lithium Ion batteries that are 2.2ah, so am expecting significant more running time.

I also tested the litium Ion vs LiFePO4 batteries on full charge in cheap identical Lithium Ion flash lights and got the same result -LiFePO4 dimmer for first hour, then the same run time.

One other test I did was to put the LiFePO4 batteries in a charger that doesn't support them (Lithium Ion charger), and they charged to 4.18v, but within approx 30mins the voltage dropped to 3.35v without using them. Pretty sure a lot of that abuse would ruin the battery, but they barely got warm during charging.
 
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Dave_H

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One may get away with using LiFePO4 in a circuit charging them to 4.2v, but expect lower life; how much lower I could not say. I have a solar LED rope light with 90 (!) green LEDs, which has operated for a couple of years every day, from the same 14500 cell. Without looking inside (though I have) I can tell they pay attention to not over-charging or over-discharging in this product.

Dave
 

Big Easy

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One may get away with using LiFePO4 in a circuit charging them to 4.2v, but expect lower life; how much lower I could not say. I have a solar LED rope light with 90 (!) green LEDs, which has operated for a couple of years every day, from the same 14500 cell. Without looking inside (though I have) I can tell they pay attention to not over-charging or over-discharging in this product.

Dave
That's the thing though, they're not overcharging. I did more test today, having them again in more light than they'll ever see being attached to where I put them up. It's 5:59pm here, they've been charging all day in the solar lights and I just now checked them. The Lithium Ion batteries in the same solar charge lights are at 4.18v, the LiFePO4 battery is at 3.23v now after charging all day in the same solar lights.
Maybe the lights have something in the circuitry (doubt it) or the LiFePO4 batteries are designed to not be overcharged so easily?
Like I told, with no batteries in the solar lights, measured at where the batteries go, they are putting out 5v in direct light, but with batteries in, they won't go over their recommended charge max, and the LiFePO4 batteries are staying just above their nominal voltage (3.20v).
 

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