eBike Battery Capacity Tester with LTC4151 & LCD Shield

BatteryTester.ino

/** Battery Characteriser

    Arduino ???
    LTC4151 power monitor
    Load, 2x paralleled 10Ω 200Watt power resistors
    DS18B20, 4x temperature sensors
    Fans, 2x 120mm PWM-controlled PC FANs
    SD Card, for logged data
    LCD Display and keypad http://www.hobbytronics.co.uk/arduino-lcd-keypad-shield?keyword=LCD%20Shield

*/
#include <SD.h>
#include <Wire.h>
#include <OneWire.h>
#include <DallasTemperature.h>
#include <LiquidCrystal.h>
// LTC4151 library?

/** Settings */
#define BAUD_RATE          (115200)
#define CELL_VOLTAGE_MAX   (4200) // in milliVolts
#define CELL_VOLTAGE_MIN   (2800) // in milliVolts
#define RATE_READ          (200) // ms between I2C reads
#define RATE_SCREEN        (100) // ms between screen updates
#define LTC_ADDR           (0xD4)

/** Masks */
#define BUTTON_NONE     (0x00)
#define BUTTON_UP       (0x01)
#define BUTTON_DOWN     (0x02)
#define BUTTON_LEFT     (0x04)
#define BUTTON_RIGHT    (0x08)
#define BUTTON_SEL      (0x10)

/** Pin Map */
#define PIN_BUTTONS     A0
#define PIN_LCD_DB4     4
#define PIN_LCD_DB5     5
#define PIN_LCD_DB6     6
#define PIN_LCD_DB7     7
#define PIN_LCD_RS      8
#define PIN_LCD_EN      9
#define PIN_BACKLIGHT   -1
#define PIN_TEMP_SEN    -1
#define PIN_FAN_PWM     -1
#define PIN_FAN1_TAC    -1
#define PIN_FAN2_TAC    -1
#define PIN_LOAD_ENB    -1
#define PIN_SD_SEL      -1

/** Class instantiations */
File logFile;
OneWire oneWire(PIN_TEMP_SEN);
DallasTemperature temp_sensors(&oneWire);
LiquidCrystal lcd(PIN_LCD_RS, PIN_LCD_EN, PIN_LCD_DB4, PIN_LCD_DB5, PIN_LCD_DB6, PIN_LCD_DB7);
char fileName[] = "LOGGER00.CSV";
byte get_button(void);
// get power
// calc temp
// enum for LCD menu

struct _bat_status {
  unsigned long timestamp;
  unsigned long voltage;
  unsigned long current;
  bool load_en;
  int temp[5];
};

void setup(void) {

  pinMode(PIN_BUTTONS, INPUT);
  pinMode(PIN_BACKLIGHT, OUTPUT);
  pinMode(PIN_FAN_PWM, OUTPUT);
  pinMode(PIN_FAN1_TAC, INPUT);
  pinMode(PIN_FAN2_TAC, INPUT);
  pinMode(PIN_LOAD_ENB, OUTPUT);
  pinMode(PIN_SD_SEL, OUTPUT);

  analogWrite(PIN_BACKLIGHT, 128);
  analogWrite(PIN_FAN_PWM, 0);
  digitalWrite(PIN_LOAD_ENB, LOW);
  digitalWrite(PIN_SD_SEL, HIGH);

  Serial.begin(BAUD_RATE);

  Wire.begin();

  lcd.begin(16, 2);
  lcd.setCursor(0, 0);

  temp_sensors.begin();

}

void loop(void) {
  // put your main code here, to run repeatedly:

}

/** Reads keypad */
byte get_button(void) {
  byte button_pressed = BUTTON_NONE;
  unsigned int ana_value = analogRead(PIN_BUTTONS);

  if (ana_value < 60) button_pressed = BUTTON_RIGHT;
  else if (ana_value < 200) button_pressed = BUTTON_UP;
  else if (ana_value < 400) button_pressed = BUTTON_DOWN;
  else if (ana_value < 600) button_pressed = BUTTON_LEFT;
  else if (ana_value < 800) button_pressed = BUTTON_SEL;

  return button_pressed;
}

/** Calculate temperature
    Maths taken from here: https://learn.adafruit.com/thermistor/using-a-thermistor
    @param voltage The read voltage in microvolts
    @returns The temperature in °C as a float
*/
float calc_temp(unsigned int voltage) {
  const float beta = 4390.0; // https://uk.farnell.com/panasonic-electronic-components/ertj1vs104fa/thermistor-ntc-0603-100k/dp/1892612
  const float nom = 100000.0; // 100kΩ at 25°C
  const float rtc = (25.0 + 273.15);

  float steinhart = 0.0;
  steinhart = (voltage / 10000000.0) / nom;
  steinhart = log(steinhart);
  steinhart /= beta;
  steinhart += 1.0 / rtc;
  steinhart = 1.0 / steinhart;
  steinhart -= 273.15; // convert to °C

  return steinhart;
}

/** read LTC4151 */
struct _bat_status get_power(void) {
  const int a_lsb_to_uv = (10000); // 20uV per LSB & 2mΩ
  const int v_lsb_to_uv = (25000); // 25mV per LSB
  const int t_lsb_to_uv = (500); // 500uV per LSB
  byte data_buffer[6];
  byte com_status;
  struct _bat_status battery_status;

  battery_status.timestamp = millis();
  battery_status.load_en = (digitalRead(PIN_LOAD_ENB) == HIGH) ? true : false;

  // read registers
  Wire.beginTransmission(LTC_ADDR);
  Wire.write(0x00);
  com_status = Wire.endTransmission(false);
  Wire.requestFrom(LTC_ADDR, 6, true);

  for (int i = 0; i < 6 && Wire.available(); i++)
  {
    data_buffer[i++] = Wire.read();
  }

  battery_status.current = (data_buffer[1] << 8) | data_buffer[0] & 0x0FFF;
  battery_status.current *= a_lsb_to_uv;
  battery_status.voltage = (data_buffer[3] << 8) | data_buffer[2] & 0x0FFF;
  battery_status.voltage *= v_lsb_to_uv;
  battery_status.temp[0] = (data_buffer[5] << 8) | data_buffer[4] & 0x0FFF;
  battery_status.temp[0] *= t_lsb_to_uv;
  battery_status.temp[0] = int(calc_temp(battery_status.temp[0]));

  // read DS18B20 sensors
  temp_sensors.requestTemperatures();
  byte num_sensors = temp_sensors.getDeviceCount();

  for (int i = 0; i < 4; i++)
  {
    if(i < num_sensors) battery_status.temp[1 + i] = temp_sensors.getTempCByIndex(i);
    else battery_status.temp[1 + i] = -300;
  }

  return battery_status;
}

To do:

• Test program
• Run capacity calculations during program
• Remove load and calculate internal resistance periodically, helps to detect bad cells

Notes:

• Works well, now adds calculations into excel sheet
• Won't do capacity calculations on the fly, better suited to Excel

Further To do:

• Add DS18B20 code to allow for load temperature monitoring
• Add code for over temperature shutdown
• Add 2x16 LCD display for detailed headless/PCless feedback