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How to chose the right battery capacity and cells?

How to chose the right battery capacity and cells?

  • Sunday, 06 August 2017
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This blog mainly discuss the Li-Mon2 18650 cells, because it is most popular use on our electric bikes. For more information about LiFePO4 and the other cells please search on internet get more message. The other blog is why LiFePO4 battery is not common use on ebike and ebike kits.

First we list the common sells we normally use.

SamsungModel NO CapacityDischarge rate
18650-22PT2200mAh5C
18650-26HM2600mAh2C
18650-29ET2900mAh3C
Panasonic18650PF2900mAh5C
18650B3400mAh2C
Sanyo18650GA3500mAh5C
LG18650M2600mAh5C
China cells186502200mAh5C
186502500mAh5C


Those are common use Li-Mon2 cells for electric bike and electric bike conversion kit. But it not means don't more capacity use. 

As we know 18650 cells voltage is 3.7v, capacity as sheet show. And you could also see that discharge rate 2c /3c /5c. 2c battery mainly use on low wattage motor ebike and ebike kit. 3c / 5c is better use on larger wattage motor e bike and e bike kit.

What is 2c / 3c / 5c ?

The general charge and discharge current size of the commonly used charge and discharge magnification to that,

That is: charge and discharge rate = charge and discharge current / rated capacity; For example: rated capacity of 100Ah battery with 20A discharge, the discharge rate of 0.2C. Battery discharge rate C, 1C, 2C, 0.2C is the battery discharge rate: a measure of the speed of discharge. The capacity of 1 hour discharge is completed, known as 1C discharge; 5 hours discharge is completed, it is called 1/5 = 0.2C discharge. The discharge capacity of the battery can generally be detected by a different discharge current. For the 24AH battery, the 2C discharge current is 48A and the 0.5C discharge current is 12A.


So before order battery we match the right discharge rate.
Match 250w hub motor electric bike and electric bike conversion kit Samsung 2600mah cells, and panasonic 3400mah cells. The other wattage for example 350w 500w 750w 1000w and 1500w it is better use 3c and 5c cells.

About battery voltage and capacity:


Each of 18650 cells voltage is 3.7v, when you need a
36v battery pack, you should series 10 cells together, 10x 3.7v =37v
48v battery pack, will 13s =13 x 3.7v =48.1v
........................................

Capacity is different, for example when your want a 10.4Ah Samsung 2600mah cells battery pack.
It is 4 Pcs cells 4 in parallel together = 4 x 2.6Ah = 10.4Ah
14.5Ah Samsung 2900mah cells will be 5s   5 x 2.9Ah = 14.5Ah

So when you need a
36v 10.4Ah Samsung cells battery pack, it is 10s x 4p = 40 Pcs Samsung 2600mah 18650 cells.
48v 14.5Ah Samsung cells battery pack, it is 13s x 5p = 65 Pcs Samsung 2900mah 18650 cells.


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