LiFePO4 battery manegement

This page documents the battery/bike monitoring system I'm building for this project. If you are interested you can get your own circuit board for building this system here:  BatchPCB.

Description: This is a board I designed to monitor the A123-systems cells in my electric bike project.  The function of the board is to monitor all the relevant  operational variables of the bike and report a simplified view to the rider. It also is in charge of shutting the bike down if any of the cells are too unbalanced or low. I also wanted the ability to log data to an SD card for later analysis of efficiency and performance.  The battery inputs are 16 LT1990 op-amps multiplexed into two MCP3553 ADC's. There are digital inputs for user buttons, a 1-wire temperature sensor and a speedometer. An rs-232 serial port allows communication with an Alltrax AXE motor controller and a logic level serial port communicates with an LCD for information display. There is a Batt+ input for detecting the presence of the battery pack, and to provide power for the 3 relay outputs.  The relays are designed to operate a main contactor, and the Keyswitch/Halfspeed inputs of the AXE motor controller.  A DosOnChip module from SparkFun allows easy data logging to an SD card. Processing power is provided by a Microchip DSpic33FJ128GP804 and a standard Microchip ICD2/3 programming header is provided.

The LCD I use is a 128x64 serial graphical unit from SparkFun but any LCD with a serial interface could be used.

Here are some pictures of the top and bottom of my board. You'll notice that the bottom has some wires hacked on. The reason for this is that my board was the prototype, and I made some improvements to it before posting it to BatchPCB.  Any of the boards ordered from there will not require any modification.

Parts list lifepo4_partslist.txt

Display:

I built a custom display module that incorporates the LCD, buttons, and some LED indicators. The PCB is available on batchPCB as well. Firmware for this board is available on https://sourceforge.net/projects/serialglcd/ The code for this module is in the firmware/branches/e-bike_display directory of the SVN tree.

Source code:

Currently in development. I'm using FreeRTOS as a base for the code, and it is making my life much easier. I have code written to monitor the speedometer and button inputs, and to calculate speed and distance. I'll post the code as soon as it will do something useful. This weekend I'm going to try to get the LCD interface working. Then I could use it as a speedometer until the rest of the code is finished.

Application