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Old 11-04-2006, 02:20 AM
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jdetray
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Default RE: Battery ? from a dummy

Hi Jamie-

I'll take a shot at explaining this.

This nomenclature tells you how many individual cells are in a battery pack and how they are connected. In theory, you can describe any type of battery pack this way, but it's most often used to describe lithium-polymer packs.

The first number (the "S" number) tells you how many cells are connected in Series (S for Series). From this, you can determine the voltage of the pack.

A single lipo cell has a nominal voltage of 3.7V. So a 3S pack is a bank of 3 cells connected in series and has a voltage of 3 x 3.7 = 11.1V. A 4S pack is a bank of 4 cells connected in series and has a voltage of 4 x 3.7 = 14.8V. A 5S pack = 18.5V. A 6S pack = 22.2V, etc.

The second number (the "P" number) tells you how many of these series-connected banks are connected in parallel (P for Parallel). The larger the number of banks connected in parallel, the greater the capacity of the pack.

Examples:

A 3S2P pack has two 3-cell banks connected in parallel, a total of 6 cells. The voltage is 11.1V, and the capacity is twice that of a single bank of 3 series-connected cells.

Let's assume you are using cells with a capacity of 2000 mAh.

Then a 3S2P pack will have a voltage of 11.1V and a capacity of 2 x 2000 = 4000 mAh.

Using the same 2000 mAh cells, a 3S3P pack (9 cells) will have a voltage of 11.1V and a capacity of 3 x 2000 = 6000 mAh.

A 5S3P pack (15 cells) will have a voltage 18.5V and a capacity of 3 x 2000 = 6000 mAh.

Packs with the designation "1P" have only one bank of series-connected cells. So a 4S1P pack consists of one bank of 4 cells connected in series. The "1P" is often omitted when describing packs with only one bank of cells, so when you hear a pack referred to as (for example) "3S" that usually means a pack consisting of 3 cells connected in series.

- Jeff
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