Voltage drop during charging and charger improvements

[sraillard]

The documentation recommend to set to 29.2v the voltage of the docking station.

When charging, the current is going through:

• D3 and D2 diodes
• R51 shunt
• Q6 mosfet

The total voltage drop is around 0.7v, meaning that the battery can only get 28.5v (so it can't be fully charged). Also, in the low level code, the charging is enabled until the battery reach 29v (that is impossible), so the battery is in float charging, something not optimal for Li-ion batteries.

Most of the voltage drop are in D3, D2 and Q6. The shunt value can be increased to improve its precision, for example with a value of 0.01R or 0.02R (the voltage will still be negligible).

A better way to manage the charging could be increasing the docking station voltage, then detecting when the charging current is under 50mA, disabling the charging until the battery voltage drop like 0.5v.

[houk001]

And that is ok. Battery is 7 cell Li-Ion pack so 7 x 4.1V full charge cell is 28.7V. This is not LiPo battery where you have 4.2V full charge per cell 0.2V margin of error and you have 28.5 for battery and also extend battery life for about year or two :D