Battery Charge Controller

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Battery Charge Controller (BCC) (other names: Battery Charge Module, BCM) - is an electronic board, placed near each of the battery assemblies to control battery current, charge/discharge process, voltage, provide short-circuit protection. This board could be described as, from one side, connected to all outputs of the battery assembly power lines, and, from the other side - as connected to a more general, higher-level controller via digital interface (I2C is preferred).

A battery charge controller design (preliminary). F1 is a PTC resettable fuse (9A holding current, 18 Amps trip).

Notice, that each battery of the pack (assembly) is charged and controlled separately.

Also, preliminary design lacks the current sense for Power output (Pwr_Out) <todo: add it later>.


Battery assembly

The 22.2 V battery assembly consists of group of batteries, connected parallel and in series. The following image describes minimal battery block.

Battery block single.png

It can be seen that there are three sense channels A, B and C (which is also an output rail of block) and a common rail - GND. They may be used to detect each battery cell charge level. Below channel names, there is a nominal voltage of battery, relatively to GND. Assembly consists of two such 11.1 blocks, connected in parallel. This block is actually a contents of typical laptop Li-Ion battery without plastic pack and controller. They are connected such way, since the robotic schematics requires about 24VDC for wheel driving motors.

The assembly scheme and rails are described on picture below:

Below is the image of a battery assembly (on the left), and its pinout on the right. The model of fuse is: MF-R900-0-99 PTC (resettable). Total output voltage is 22.2V. Capacity is 4800 Ah.

Battery assembly.png

Since GND rail is fused, the sum of currents in each rail must be less than maximal fuse shut down current:
<m>I_A+I_B+I_C+I_D+I_E+I_F < I_{fuse}</m>

Absolute maximal ratings

<maximal charge, discharge, forward voltage, drained current, charge current, temperature etc>

Charging theory

Measuring discharge current: <m>I_{discharge} = \frac {max(U - Us, 0)}{R_s};</m>

Charge current is: <m>I_{charge} = \frac {max(Us - U, 0)}{R_s};</m>

<Todo: write information about CV-CC charge curves here for battery assembly>


See also

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