heat tolerance for li-ion

I'm planning to set up a solar charging device which would store energy in li-ion cells. I'm just wondering if the heat from being under the sun would affect the cells? Would NiMH be better for this?

I don't think the heat would be a problem (as long as you are not planning to put them in direct sun at 50°C).

But for Li-ion you will need a charge controller between the solar panel and the battery. With NiCd (and to a lesser extent NiMH) you will not need such a controller. So NiCd may be more economical overall. A lead acid accumulator may be more economical still (though that will also need a charge controller and is more suitable for large applications).

That's cool, would NiMH also be OK with the heat?

Most batteries perform best in the 20°C to 25°C range. Try not to let them get hotter than that if you can help it, or their performance will suffer.

Aww man, I was afraid of that cos I plan to have the cells housed in the same enclosure right beneath the solar panels.

Mr Happy said:

Most batteries perform best in the 20°C to 25°C range. Try not to let them get hotter than that if you can help it, or their performance will suffer.

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but being under the sun, wont they get hotter than 25C? my place here is always in the range of 30-32C :huh:

Li-Ions discharge best at 50°C, but I don't know that anyone's ever tested the effects of temperature and charging.

To obtain the optimum capacity and cycle life of a NiMH battery, the recommended range of
temperature when discharging a standard battery is 0°C (32°F) to 40°C (104°F).




Anders

hi,
a rather silly question here. rechargeable batts are often said to have about 1000 rechargeable lives on their packagings. so if i were to trickle charge them over 3 days (overnight), does it mean "3 lives" are used up

ruriimasu said:

if i were to trickle charge them over 3 days (overnight), does it mean "3 lives" are used up

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The 1000 "lives" are charge/discharge cycles at whatever the manufacturer feels the normal rate is. Charging or discharging at a lower/slower rate can actually make the battery last longer.

StarHalo said:

The 1000 "lives" are charge/discharge cycles at whatever the manufacturer feels the normal rate is. Charging or discharging at a lower/slower rate can actually make the battery last longer.

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It can also make the battery wear out more quickly.

The 1000 cycles is always preceded by "up to". In reality, 200 to 500 cycles is a more likely expectation, if you look after the batteries well. Less if you don't.

so is trickle charging them with solar for 3 days considered as 3 cycles? im still confused.

and also, if i place them in a normal charger for 10mins and decide to switch off the charger and switch it on after a few mins or hours, is that considered 2 cycles?

ruriimasu said:

so is trickle charging them with solar for 3 days considered as 3 cycles? im still confused.

and also, if i place them in a normal charger for 10mins and decide to switch off the charger and switch it on after a few mins or hours, is that considered 2 cycles?

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It depends on many things, and it is really impossible to say. When the specifications say a battery will last for 500 cycles that doesn't mean it will work fine for 500 cycles and then stop working at cycle 501. The battery will gradually fade over time, becoming less and less efficient as time and usage mount up. You get to choose when you think it is not working well enough for your purposes any more.

However, solar trickle charging is not necessarily good for NiMH cells. NiCd cells are better suited to that application as they are more robust and can better tolerate continuous trickle charging.

Mr Happy said:

However, solar trickle charging is not necessarily good for NiMH cells. NiCd cells are better suited to that application as they are more robust and can better tolerate continuous trickle charging.

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mr happy, thanks for the information. i've ordered a few parts off DX and kaidomain and am waiting for all the parts to arrive before i DIY my on solar charger. initially i wanted to use it to recharge NiMH AAs, specifically Recyko AAs. now after hearing what you said, i was thinking maybe to use it to recharge li-ions such as 18650 or 10180s. my solar panel is rated 5V 130ma, do you think it would be enough for the li-ions or maybe i should just stick with my Recykos? i'll be putting a diode at the solar panel side to prevent charge from the batteries to flow out.

ruriimasu said:

i was thinking maybe to use it to recharge li-ions such as 18650 or 10180s

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No!!

See post #2. You must never charge Li-ion without a proper charge controller between the power supply and the battery.

This is another thread where it would behoove the interested parties to read and get a proper foundation from www.batteryuniversity.com

Mr Happy said:

No!!

See post #2. You must never charge Li-ion without a proper charge controller between the power supply and the battery.

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can i then use the charger to charge two AA Recykos? the solar panel is 5V 130ma.

LuxLuthor said:

This is another thread where it would behoove the interested parties to read and get a proper foundation from www.batteryuniversity.com

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i read from the website that the current is usually higher than whats claimed and the solar panel actually works better in a cooler temperature. can i use a 5V panel to charge up two AA Recykos (2.4V combined)? my setup is a tin canister and the solar panel on top of the canister and the batteries in it. with this setup, i will need to keep it in the sun and it will bake the batteries in it as well during charging. can i put black tape or something dark in the inside of the canister to dissipate heat? the outside it shiny though so i guess it will reflect away heat.

If it were me, I would find a way to measure the temp where the batteries are, and see what is actually going on during hotter times. You could experiment with some ways of insulating the batteries from direct heat, including fiber insulation or moving them away from any surface radiating heat from direct sun. Black generally attracts sunlight heat.

As Mr Happy said, you need a proper Li-Ion power charge regulator, I don't know what a "Recykos" AA is.

If you are using a fixed trickle output, only NiCad cells will hold up.

Hello Ruriimasu,

The GP ReCyko, and other low self discharge cells, are sensitive to heat. They loose their low self discharge properties when they get hot. I don't know if that loss is permanent or temporary.

Tom

SilverFox said:

Hello Ruriimasu,

The GP ReCyko, and other low self discharge cells, are sensitive to heat. They loose their low self discharge properties when they get hot. I don't know if that loss is permanent or temporary.

Tom

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hi tom. how about when it gets hot after charging off AC? i used a sanyo 2hr charger and it got really very very hot after the charges. will that damage the LSD properties?