Newbie Terminology Question

[tomcat017]

Hi Everyone,

Sorry to post a newbie question, but my searching was unsuccesful. I've been trying to read a lot of battery/electronics threads, because that is the part that I understand the least (especially charging and discharging rates, etc, etc--any recommended resources? ) Annyway, the question is this: sometimes I see people refer to charging to "2C." Or "only a discharge rate of 1C." Particularly when discussing safety of batteries, etc. I'm sure I'm using those incorrectly, but I hope you know what I mean. What is the C all about? When I tried searching, all I found was 3C [cell] lights, etc. So...any help would be greatly appreciated. Thanks!!

 

[Anders]

Hello tomcat017.

C refers to the advertised capacity of the cell
.
If you for example have a 2500 Nimh cell and charge it with 2C, its the same as 5A for this particular cell (sounds much).
Discharge the same cell with 1C is the same as 2500 mA.

Anders

 

[tomcat017]

Hey Anders,

Thanks for the info! So does this mean that a cell with an advertised capacity of 2500mAh can be charged to twice that?! Thanks again,

-mike

 

[DonShock]

...So does this mean that a cell with an advertised capacity of 2500mAh can be charged to twice that?!...

No, it refers to the RATE at which you can charge or discharge. 2C means two times the capacity. So if a cell is rated at 2500 mAH, that means the approximate total power held in the cell expressed as current (mA) times the time at that current (in Hours) is 2500. For example, it should supply around 500mA for around 5 hours, 1000mA for around 2.5 hours, 1250mA for around 2 hours, etc. The capacity of the cell is also often used to determine how fast you can put juice into (charge) or out of (discharge) the cell, that's what the 2C is about. So if the max recommended discharge rate on a 2500 mAH cell is 2C, you take the current part of the capacity (2500mA) and multiply it by 2 to get a maximum discharge rate of 5000mA (or 5A). You will also see this term used when they specify how they came up with the capacity figure. They may state the capacity as 2500mAH "at 0.1C". That essentially means that they came up with that number by discharging the cell at 250mA and it lasted 10 hours. In general, as you discharge a cell at higher and higher currents, you will have less and less capacity you can get from the cell. So if you discharge the cell at 2C, instead of 0.1C, you may only have 2000mAH of capacity. Basically, you are pulling power from the cell faster than the chemical reactions inside the cell can produce it. So The charge and discharge limitations are intended to limit how fast this conversion between electrical power and chemical reactions occurs to prevent damaging the cells.

 

[LuxLuthor]

To say what Don said in your example:

2500 mAh advertised battery means in that case 1C = 2500 mA (2.5A) charging rate.

With a 1200 mAh battery, 1C = 1200 mA (1.2A) charging rate.

For a given battery, the manufacturer says what is the safe "C" value to then calculate your charge/discharge rate, and it varies with the quality of how they are made, the type of battery chemistry (NiCd, NiMH, LiPo, Li-Ion), and the quality of the charger used.

 

[tomcat017]

Thanks guys! Makes perfect sense now--and that makes this newb one happy flashoholic . lol--thanks!