Power Board
From HotDec
Contents |
Introduction
The power board (charging board) allows the hovercraft to automatically charge its batteries while at the docking station. The power board also allows the SBC and MCU to run off the docking station power (AC power) instead of power from the batteries.
Testing
Explainations
Zero Volt Charging Mode
If at some point the battery voltage drops below 80% of the battery depleted threshold (which is set to about 5v? on the power board) the charger chip goes into zero volt charging mode. There are 3 reasons why the battery voltage could be less than the depleted voltage threshold
- The battery is totally drained.
- There is no battery plugged in, and the board has just got ac power.
- There is a short on the charger output.
Zero volt charging mode is really a protective measure for third case. In zero voltage charging mode the charging controller turns off the charging mosfet completely. Then the chip connects the charging output to the AC input through a 750 ohm resistor. This allows a very small amount of current to get to the output. In the case no battery is plugged in this small amount of current should be enough to raise the output voltage about the battery depleted threshold and allow the charger to return to the normal charging mode.
Changes
There have been a couple of modifications made to the power board that differ from the OrCAD schematic/layout. Most of these changes are resitors values.
- R49 and R96 have been changed from 430ohms to 499ohms. This reduces the max charging voltage slightly, hopfully increasing battery life.
- D32 the 'SBC Connected' LED has been replaced by a two pin header. The LED is useful for debugging purposes, but needlessly drains the SBC battery when the SBC is running off the docking station power.
- R3 has been changed from 200K to 100K
- R5 has been changed from 200K to 20K
