Arduino/Genuino Lead Acid Battery Tester

Shield "LEO" and the Add-on "BRUNO"

✈ Charging Batteries - A short overview

✈ The "Shield"

The shield (LEO) was originally designed for another project (yet unpublished), but is recycled here to keep the development time short. It is an universal I/O board. You don't absolutely need it, but it made my life easier :-)

✈ The "Add-on"

The second board is more or less the 'power-stage'. It can switch the charger on or off. A DAC (MCP4822-E/P) sets the current to discharge the battery with a constant current. The current and the voltage of the battery are measured during the charging and discharging period. With that, the amount of charge can be estimated. (ISA-PLAN® 1 Ω Precision resistor and High Voltage, Bidirectional Current Shunt Monitor AD8210). After the start button has been pressed, the battery is charged for 12 hours with a constant voltage of 13.8 volt. Then the charger is disconnected and a small pause is granted to the battery. After that it will be discharged until the voltage drops below 10.8 volt. The sketch will send a group of measurements every 60 sec. Therefore the Serial Plotter which is available from version 1.6.6 (Arduino.cc) mayst be unable to cope and we suggest you copy and paste the values into the spreadsheet of your choice. A temperature monitoring is also available. When testing lead-acid batteries, this is not absolutely necessary - and so we use it to monitor the temperature of the heatsink.

✈ Arduino Sketch - The Code

Double click on code to select ...

/* ////////////////////////////////////////////////////////////////// 
ARDUINO/Genuino (UNO) Lead Acid Battery Tester
https://www.changpuak.ch/electronics/Arduino-LeadAcidBatteryTester.php
Software Version 1.0, 
23.06.2016, Alexander C. Frank
////////////////////////////////////////////////////////////////// */

#include <LiquidCrystal.h>
LiquidCrystal lcd(9, 8, 6, 5, 4, A5);

const int TemperaturePin = A2;
float TemperatureValue = 0.0;

const int KeyBoardPin = A0;
unsigned int KeyPressed = 0;

const int VoltagePin = A3;
float Voltage = 0.0;

const int CurrentPin = A1;
const float ZeroCurrent = 2.495;
float Current = 0.0 ;    // MILLIAMPS

const int ChargerOn = A4;
const int CS = 13;
const int SCLK = 12;
const int SDAT = 11;
const int LOAD = 10;

float ChargeWattHour = 0.0; // in Wh

unsigned long DeltaTime = 0;
unsigned long LastTime = 0;
unsigned long DisplayTime = 0;
unsigned long StartTime = 0;
unsigned long StopTime = 0;
unsigned long TimeBase = 9999;  // 10 sec
unsigned long TargetCurrent = 0;

// ////////////////////////////////////////////////////////////////// 

const unsigned long ChargeTime = 18000;       // SECONDS
const unsigned long Pause = 600;              // SECONDS
const float StopDischargeVoltage = 10.5 ;
const unsigned long DischargeCurrent = 700 ;  // MILLIAMPS
boolean ChargeFirst = true ;        // NO GO DIRECTLY TO DISCHARGE TEST 

// ////////////////////////////////////////////////////////////////// 

void UpdateTemperature() 
{
unsigned int aux = 0;
for (int i=0; i<2; i++){ aux += analogRead(TemperaturePin); delay(10);}
// LM35 gives 10mV per degree. We amplify by 5. 5V = 100 deg
TemperatureValue = aux / ( 2.0 * 10.24 );
}

// ////////////////////////////////////////////////////////////////// 

void UpdateCurrentRead() 
{
unsigned int aux = 0;
for (int i=0; i<32; i++){ aux += analogRead(CurrentPin); delay(10);}
// AD8210 gives 20 x U (= 20 * I * 0.1 Ohms)
Current = ((5.0 * aux / ( 32.0 * 1023 )) - ZeroCurrent) / 2.0  ;
Current = 1000.0 * abs(Current);
}

// ////////////////////////////////////////////////////////////////// 

void UpdateCurrentWrite(unsigned int TargetCurrent) 
{
// WE USE THE DAC OF CHANNEL A, SHUNT IS 1 OHM
unsigned int pointer = 0x8000;
unsigned int DACA = (int)( TargetCurrent );
  DACA |= 0x1000;   // GAIN = 2, DON'T SLEEP, Write to DACA
  digitalWrite(CS, LOW);
  for (int i=0; i < 16; i++) {
    if ((DACA & pointer) > 0) 
      { digitalWrite(SDAT, HIGH); }
        else { digitalWrite(SDAT, LOW); }
    digitalWrite(SCLK, HIGH);
    digitalWrite(SCLK, LOW);
    pointer = pointer >> 1;
  }
  digitalWrite(CS, HIGH);
  digitalWrite(LOAD, LOW);
  digitalWrite(LOAD, HIGH);  
}

// ////////////////////////////////////////////////////////////////// 

void UpdateVoltage() 
{
unsigned int aux = 0;
for (int i=0; i<4; i++){ aux += analogRead(VoltagePin); delay(10);}
// Resistor Divider: A3 = U * 3/(3+12) 
Voltage = 1.0134861 * aux / ( 4.0 * 40.92 );
}

// ////////////////////////////////////////////////////////////////// 

void UpdateChargingScreen() 
{
unsigned int HH, MM, SS, REST ;
lcd.clear();
lcd.setCursor(0,0); lcd.print("*** CHARGING ***");
lcd.setCursor(0,1); lcd.print("TOGO ");
HH = DisplayTime / 3600 ;
REST = DisplayTime - HH * 3600 ;
MM = REST / 60 ;
SS = REST % 60 ;
if(HH < 10) lcd.print("0"); lcd.print(HH); lcd.print(":");
if(MM < 10) lcd.print("0"); lcd.print(MM); lcd.print(":");
if(SS < 10) lcd.print("0"); lcd.print(SS); lcd.print(" ");
lcd.setCursor(0,2); 
if(Voltage < 10) lcd.print(" ");
lcd.print(Voltage,2); lcd.print(" V ");
lcd.setCursor(9,2); 
if(Current < 1000) lcd.print(" ");
if(Current < 100) lcd.print(" ");
if(Current < 10) lcd.print(" ");
lcd.print(Current,0);lcd.print(" mA ");
lcd.setCursor(0,3); lcd.print(TemperatureValue,1); lcd.print(" "); 
lcd.print((char)223); lcd.print("C ");
}

// ////////////////////////////////////////////////////////////////// 

void UpdateDischargeScreen() 
{
unsigned int HH, MM, SS, REST ;
lcd.clear();
lcd.setCursor(0,0); lcd.print("*** TESTING ***");
lcd.setCursor(0,1); lcd.print("ELAPSED ");
HH = DisplayTime / 3600 ;
REST = DisplayTime - HH * 3600 ;
MM = REST / 60 ;
SS = REST % 60 ;
if(HH < 10) lcd.print("0"); lcd.print(HH); lcd.print(":");
if(MM < 10) lcd.print("0"); lcd.print(MM); lcd.print(":");
if(SS < 10) lcd.print("0"); lcd.print(SS); lcd.print(" ");
lcd.setCursor(0,2); 
if(Voltage < 10) lcd.print(" ");
lcd.print(Voltage,2); lcd.print(" V ");
lcd.setCursor(9,2); 
if(Current < 1000) lcd.print(" ");
if(Current < 100) lcd.print(" ");
if(Current < 10) lcd.print(" ");
lcd.print(Current,0);lcd.print(" mA ");
lcd.setCursor(0,3); lcd.print(TemperatureValue,1); lcd.print(" "); 
lcd.print((char)223); lcd.print("C ");
}
// ////////////////////////////////////////////////////////////////// 

void UpdatePauseScreen() 
{
unsigned int HH, MM, SS, REST ;
lcd.clear();
lcd.setCursor(0,0); lcd.print("*** PAUSING *** ");
lcd.setCursor(0,1); lcd.print("TOGO ");
HH = DisplayTime / 3600 ;
REST = DisplayTime - HH * 3600 ;
MM = REST / 60 ;
SS = REST % 60 ;
if(HH < 10) lcd.print("0"); lcd.print(HH); lcd.print(":");
if(MM < 10) lcd.print("0"); lcd.print(MM); lcd.print(":");
if(SS < 10) lcd.print("0"); lcd.print(SS); lcd.print(" ");
lcd.setCursor(0,2); 
if(Voltage < 10) lcd.print(" ");
lcd.print(Voltage,2); lcd.print(" V ");
lcd.setCursor(9,2); 
if(Current < 1000) lcd.print(" ");
if(Current < 100) lcd.print(" ");
if(Current < 10) lcd.print(" ");
lcd.print(Current,0);lcd.print(" mA ");
lcd.setCursor(0,3); lcd.print(TemperatureValue,1); lcd.print(" "); 
lcd.print((char)223); lcd.print("C ");
}

// ////////////////////////////////////////////////////////////////// 

unsigned int ReadKeyBoard() 
{
unsigned int aux = 0;
unsigned int ReturnValue = 0;
// Trigger value is decimal 341 and 682
delay(10);
aux = analogRead(KeyBoardPin);
// NO KEY
ReturnValue = 0;  
// STOP KEY
if ((aux > 241) && (aux < 441)) ReturnValue = 1;
// START KEY
if ((aux > 582) && (aux < 782)) ReturnValue = 2;
// BOTH KEY
if ((aux > 440) && (aux < 583)) ReturnValue = 3;
return ReturnValue;
}

// ////////////////////////////////////////////////////////////////// 



void setup() {
  // LCD
  lcd.begin(16, 4);
  lcd.clear();
  lcd.setCursor(0,0); lcd.print("ARDUINO/GENUINO ");
  lcd.setCursor(0,1); lcd.print("SHIELD 'LEO'    ");
  lcd.setCursor(0,2); lcd.print("ADD-ON 'BRUNO'  ");
  lcd.setCursor(0,3); lcd.print("BATTERY-TESTER  ");
  // OUTPUT PINS
  pinMode(ChargerOn, OUTPUT);
  digitalWrite(ChargerOn, LOW);
  pinMode(LOAD, OUTPUT);
  digitalWrite(LOAD, LOW);
  pinMode(CS, OUTPUT);
  digitalWrite(CS, LOW);
  pinMode(SDAT, OUTPUT);
  digitalWrite(SDAT, LOW);
  pinMode(SCLK, OUTPUT);
  digitalWrite(SCLK, LOW);
  // SET DISCHARGE CURRENT TO ZERO :-)
  UpdateCurrentWrite(TargetCurrent);
  Serial.begin(9600);
  delay(2000);  
}

void loop() {
  
  // WAITING FOR START KEY PRESSED
  unsigned int pc = 0;
  lcd.clear();
  lcd.setCursor(5,1); lcd.print("PRESS");
  lcd.setCursor(5,2); lcd.print("START");
  KeyPressed = 0;
  do {
      pc += 1;
      if (pc == 60) { lcd.noDisplay() ; }
      if (pc == 120) { lcd.display() ; pc = 0 ; }
      delay(1);
      KeyPressed = ReadKeyBoard();
    }  while ( KeyPressed == 0 );
  
  StartTime = millis();
  StopTime = StartTime + ChargeTime * 1000 ;
  lcd.display() ;     
  
  // CHARGING THE BATTERY
  if ( ChargeFirst != true ) StopTime = millis(); 
  while ( millis() < StopTime ) 
  {
    DeltaTime = StopTime - millis() ;
    DisplayTime = DeltaTime / 1000 ;
    UpdateTemperature();
    UpdateVoltage();
    UpdateCurrentRead();
    delay(TimeBase);
    UpdateChargingScreen();
    digitalWrite(ChargerOn, HIGH);
  }
  digitalWrite(ChargerOn, LOW);
  StopTime = millis() + Pause * 1000 ;
  
  // SHORT PAUSE
  while ( millis() < StopTime ) 
  {
    DeltaTime = StopTime - millis() ;
    DisplayTime = DeltaTime / 1000 ;
    UpdateTemperature();
    UpdateVoltage();
    UpdateCurrentRead();    // YES, THIS SHOULD BE ZERO NOW :-)
    delay(TimeBase);
    UpdatePauseScreen();
  }

  // MEASURING THAT BATTERY
  // RAMP-UP THE CURRENT TO 100%
  UpdateCurrentRead();
  UpdateDischargeScreen();
  while ( Current < DischargeCurrent ) 
    {
    UpdateCurrentWrite(TargetCurrent);  // SETPOINT
    TargetCurrent += 1;
    delay(1);
    UpdateCurrentRead();  // MEASURES THE REAL VALUE
    UpdateDischargeScreen();
    }
  StartTime = millis();
  // NOW DISCHARGE UNTIL VOLTAGE LIMIT
  while ( Voltage > StopDischargeVoltage ) 
  {
    DeltaTime = millis() - StartTime ;
    DisplayTime = DeltaTime / 1000 ;
    UpdateTemperature();
    UpdateVoltage();
    UpdateCurrentRead();
    Serial.print(DeltaTime);Serial.print(",");
    Serial.print(Voltage,2);Serial.print(",");
    Serial.print(Current,0);Serial.print(",");
    Serial.println(TemperatureValue,1);
    UpdateDischargeScreen();
    delay(TimeBase);
  }
  // VOLTAGE LIMIT REACHED. SET CURRENT TO ZERO
  UpdateCurrentWrite(0);


}
// ////////////////////////////////////////////////////////////////// 
// END OF FILE.
// ////////////////////////////////////////////////////////////////// 

✈ Measurements on a 12 V / 7 Ah Battery (new/used)

It is advantageous to copy and paste the data rows (from the serial monitor) into a textfile. This can then be opened with the spreadsheet program of your choice.

From the "labelled" 7 Ah, one would expect the battery to deliver 7 Amps during one hour. Or 700 mA during ten hours. But the (new) battery failed to do so. Responsible for this behavior is Peukert's law, (Wilhelm Peukert, 1897). It expresses approximately the change in capacity of rechargeable lead-acid batteries at different rates of discharge. As the rate increases, the battery's available capacity decreases.

✈ Battery Comparison (Primary Elements) Size LR06, UM3, AA

TYPE/BRAND	CHF/1	Distributor	Capacity [Ah]	[Ah]/CHF
VARTA LITHIUM1	3.38	Interdiscount	2.7355	0.8093
VARTA MAX TECH2	2.24	Interdiscount	under test	-
VARTA HIGH ENERGY3	1.74	COOP	under test	-
VARTA LONGLIFE4	0.60	D-PHYS	under test	-
DURACELL SIMPLY5	1.74	COOP	2.1999	1.2643
PRIX Garantie6	0.50	COOP	2.2016	4.4032
ALKALISK7	0.30	IKEA	under test	-

VARTA says 1) is optimised for Digital Cameras, 2) for Flashlights, 3) for Toys, 4) for Remote Controls.
DURACELL says 5) is suiteable for Radios, Remote Controls, Clocks.
PRIX Garantie says 6) Do not throw into fire, keep away from children ?!?!
IKEA says 7) is suiteable for MP3-Player, Digitalcameras, Toys, Clocks, Remote Controls and more.

// ////////////////////////////////////////////////////////////////// 

const unsigned long ChargeTime = 1 ;          // SECONDS
const unsigned long Pause = 1 ;               // SECONDS
const float StopDischargeVoltage = 0.8 ;
const unsigned long DischargeCurrent = 100 ;  // MILLIAMPS
boolean ChargeFirst = false ;      // GO DIRECTLY TO DISCHARGE TEST 

// ////////////////////////////////////////////////////////////////// 

✈ Limitations

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