SparkFun Forums

[tronic]

Hey everyone - I have the 900mAh Li-Poly battery from Sparkfun (PRT-00341). I'm trying to interface it to a battery charger IC. My question is how do I determine the charge current for the battery? The spec sheet says the charge current is "Standard 0.2C5A Max 1C5A". How do I interpret that? What does the "C5" mean?

Thanks!

[coyote20000]

C stands for Capacity.
Standard 0.2C5A Max 1C5A

From what you typed, I'd say the charge current should be 0.2C.
If the capacity of the battery is 5A (I'm only guessing by what you wrote) or 5Ah (5000 mAh) then 0.2C is (0.2*5Ah) or 1A.

Dave

[tronic]

Dave - thanks for your response. It's nice to know C stands for capacity. Except this battery is not 5Ah, it's 900mAh, so I'm still confused. I should also mention that the 5 is a subscript of the C.

[redwire]

"C" is the rated capacity of the battery in amp-hours. The datasheet subscript "5" usually means the time period used by the manufacturer to calculate C. C is usually measured with discharge over a 20 hour period (C20) but this datasheet uses a 5 hour test, so read C5 as "C over a 5 hour discharge time".

Charging at 0.2C is (0.2*0.860) = 172mA.
Charging at 1C is (1*0.860) = 860mA.

Just make sure not to exceed 4.2V and at high charge currents the battery can overheat. When testing keep paper and stuff away from it.

[tronic]

Redwire,
great! This was the info I was looking for. You seem to know your stuff about batteries.

[coyote20000]

"C" is the rated capacity of the battery in amp-hours. The datasheet subscript "5" usually means the time period used by the manufacturer to calculate C. C is usually measured with discharge over a 20 hour period (C20) but this datasheet uses a 5 hour test, so read C5 as "C over a 5 hour discharge time".

Charging at 0.2C is (0.2*0.860) = 172mA.
Charging at 1C is (1*0.860) = 860mA.

Just make sure not to exceed 4.2V and at high charge currents the battery can overheat. When testing k paper and stuff away from it.

Red, just wondering why you picked .860?

[waltr]

"Standard 0.2C5A Max 1C5A"

This isn't correctly printed. In the data sheet the "5" after the "C" is a sub-script and there isn't a 1 after "Max" but a square box that probable is an embedded non-ASCII formatting character.

So the standard charge rate of 0.2C is 0.2 times 900mAhr or 180mA. There is a note near the end of the data sheet that states:
"Charging current should be lower than (or equal to) 1C 'sub-script 5' A;
So the maximum charge rate would be 800mA. But I would only use this rate if the charge controller also monitors the battery temperature.

Here is a link to a pretty good LiIon tutorial. The charging technique is a the same for LiPo, just the state change values are different.
http://www.batteryuniversity.com/partone-12.htm

[redwire]

The battery is labelled 900mAh, but the datasheet lists 860mAh... so I used that.