I started out , when at work they had pile of battery packs for laptop computers , that no longer worked. Well I know that most (not all ) Battery packs for Laptops are made up of a bunch of 18650 Li-Ion Battery Cells , and it is usually only one or 2 cells that go bad in a Pack making the entire battery pack no good. So I grabbed a Bunch of them and took them apart. My use was going to be to use them to power some Bicycle lights. Figured I would charge them up and shouldn't be too hard to find the bad cells using an Volt/Amp Meter , this Worked but not well by any means ,I soon discovered that a lot of the cells would take a charge , but not much of a charge , found this out the hard way with bike lights that went dark too fast.

So I came up with this Idea of using a Computer , with an analog input, and would read the out put of the battery across a load over time to determine how much energy the battery cell could store. My first attempt was using an old PC with a Metrabyte DAS-8 A/D board . It was basic , I would manually connect the load start teh data collection, stop it after time , and then using excel determine the amount of energy in the Cell. But I wanted to do this more automatically . I was using an Ardunio for another project ( which will soon have an instructable for it ) and realized it had all that I needed to do this . so I made the switch and it was a lot easier to wire up , program and took up a lot less space.

Step 1: Charging the Batteries

Charging LI-Ion Batteries
WARNING WARNING WARNING
when charging LI-ION batties Be careful! they can be unstable and catch fire. I have never personally had this happen , but I don't care i always take the precautions, better safe then sorry. there are plenty of horror stories out there.
1) Never Charge unatteneded!
2) Charge out doors or some place some place pretty much fire proff ( I charge mine on the Bricks of my fire place or top of Steel sheet )
3) AVOID drivect shorts
4) do not use a Physically Damaged Cell.
5) Dispose of Properly ( I take my To Home depot and deposit in there battery recycling bins )
Most of the time I use this simple charger from Deal Extreame ( http://dx.com/digital-li-ion-18650-battery-charger-6105) I also will use a larger RC Smart charger for doing multi cell packs , but that is a little beyond what this Instrucable is for.

Step 2: Parts List

Parts List
- Adrunio Uno or compatible ( ebay $20 )
- 16 X2 LCD display that uses a Hitachi HD44780 driver, They are very common, I have gotten several from old HP servers and Rolm Phones, but one can Be purchased here. for $10 http://www.adafruit.com/products/181
- An opto 22 Solid State Relay ( RED , 5 Vin ) I happen to have an ample supply around my basement
- 18650 battery Holder , $2 eBay
-10 M ohm 1/4 watt Resistor ( or something large just to be used as a Pull down )
- 4 Ohm 6 watt Resistor
- 1 push Button, momentary contact switch (not Shown )
- 6 to 10 V 500 ma , Power supply , Wall wart style to power the adrunino (not Shown)

Step 3: Theory and Operation

Theory and Operation

Li-Ion Batteries , when charged under no load have a Voltage of about 4.2 Volts , that quickly drops to about 3.9 Volts under load and slowly drops as the charge is used . a Li-Ion Battery cell is considered fully discharged then the under load Voltage get below 3.00 Volts.
So what i do it have the battery attached to one of the Adruino's Analog Input's , and read the No-load value. at the same time waiting for the start Button to be pressed. If the voltage input is above 3.00 volts when the Button is pressed the test will start.
When the test starts the Solid State relay is energized with switch the 4 ohm resistor to be a load directly across the battery. the Voltage is then read every half second and using ohm's Law current , I=V/R, R= 4 ohms and V is read from the Analog input. Since this reading is taken every half second , we know there are 7200 1/2 seconds in an an hour , we just take the current multiply it by 1/7200 of an hour and accumulate all those reading and until the Voltage is below 3.00 volts , at that point the Relay is shut off and the grand total of how many maH of energy was released is displayed

Step 4:

4) After getting the parts together First thing to do is prep and connect the LCD dispaly , I used the basic setup of an LCD display as seen on the Ardunio tutorial page ( http://arduino.cc/en/Tutorial/LiquidCrystal ) I however do not use a Potentiometer for brightness control, I just connect Pin 3 to Ground . I also Do not use the same Pins. I don't use the High end Pins, because i had ideas of putting an Ethernet/SD card Shield on and recording the data from each Battery as it was being tested , that however has not come to fruition .

back to the matter at hand the LCD display .
Pin   Destination
1   - GND
2    + 5
3       GND
4   - Digital Pin 2
5 -     Digital Pin 3
6,7,8,9,10 No connection
11   - Digital Pin 5
12 - Digital Pin 6
13 - Digital Pin 7
14    Digital Pin 8
15     + 5
16 -- GND
that will take care of wiring the LCD

Step 5:

next I take the Battery Holder . I attach the negative to Ground , and the Positive to Analog Input 0 .
Between the analog 0 input and ground i put a 10 M ohm resistor . I use this as a Pull down resistor, helps elivate noise especially when there is no cell in the holder .
Next I take the Solid state relay , attach the input "-" to Ground, and the input Positive to Digital Pin 1 . now I take the Positive ( If your SSR has polarity on the output some do some don't ) output Pin of the Solid state relay and attach it to the Positive terminal , and between the Negative terminal and Ground put the 4 Ohm 6 Watt Resistor , this will be the load resistor and give it some space because it can get hot.

finally attach a Push button between +5 and digital Pin 0 ( I actually use a SPDT ) Push button and attach the other pole to ground , that can cause a Noise spike to trigger it, or you could just use another 10 M ohm resistor as a pull down it will work too. I know its overkill, just a habit from years of work.

that Completes the wiring , next is he code and here it is . Because I'm using Pin's 0 and 1 , you might have to disconnect those to pins while you down load the program , other wise it might not load.

Step 6: The Source Code

Here is the source code for the Analyzer

/*
A battery life cycle tester using an Lcd as output
*/

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd( 2, 3, 5, 6, 7, 8 );
const int buttonPin = 0;
int sensorPin = A0;    // select the input pin for the Battery
int sensorValue = 0; // variable to store the value coming from the sensor
const int relay=1;
int buttonState = 0;
float mah = 0.0;
long timestart ;

void setup() {
// set up the LCD's number of columns and rows:
lcd.begin(16, 2);
// Print a message to the LCD.
lcd.print("Battery life tester");
pinMode(relay, OUTPUT);
pinMode(buttonPin, INPUT);
}

void loop() {
// set the cursor to column 0, line 1
// (note: line 1 is the second row, since counting begins with 0):
digitalWrite(relay, 0 ); //set the LED-relay off

while (buttonState == LOW ) {
sensorValue = analogRead(sensorPin); // read the battery
// the voltage
buttonState = digitalRead(buttonPin);
// if (buttonState == HIGH) {
//    if (bb > 0) { bb=0; } else { bb=1; }
// }
lcd.setCursor(0, 1);
lcd.print((sensorValue*4.98)/1023);
lcd.print(" Volts");
delay(500);
} //end get ready loop
digitalWrite(relay, 1 ); //set the LED-relay on
lcd.setCursor(0, 0);
lcd.print("Testing              ");
lcd.setCursor(0, 1);
lcd.print("                         ");
mah = 0.0;
timestart = millis( );
while ( ((sensorValue*4.98)/1023) > 3.00 ) {
     lcd.setCursor(0, 1);
     lcd.print((sensorValue*4.98)/1023);
     lcd.print(" V ");
     sensorValue = analogRead(sensorPin); // read the battery
     mah = mah + (((sensorValue*4.98)/1023)/4 )/7.2;
     lcd.print(mah);
     lcd.print(" mAh ");
     delay ( 500 ) ;
     lcd.setCursor(8,0);
     lcd.print((millis( )- timestart)/1000); // time since test staarted
} // end battery drain
    digitalWrite(relay, 0 ); //set the LED-relay off

// final results

   lcd.setCursor(0, 0);
   lcd.print(mah);
   lcd.print(" mAH ");
   lcd.print((millis( )- timestart)/1000);
   lcd.print(" S ");
   buttonState = digitalRead(buttonPin);

}

Step 7: Run It

First put a charged battery In the Holder . Note the voltage above 3.0

Step 8: Out the Battery Under Load

Press the start button and watch and Wait. On top displays the seconds that have elapsed 83 seconds in this case
the current voltage reading ,3.64 Volts , notice how much it dropped under a 1 amp load. and finally how much energy in Millamp Hours has been discharged, 21.06 Mah .

Step 9:

And when it completes , the Top line has the total Energy that was in the cell, 629.24 Mah and how long it took, 2788 seconds or 46 Minutes and 28 seconds. in this case this is not a battery I would keep . I don't keep any under 1000 Mah,. and it has reset it self just waiting for you to press the button again and start the test going again.

Step 10: What I'd Still Like to Do .

I would like to record the data Points to an SD card and then have the data accessible from a Web page through an Ethernet Shild , thats Why I didn't use Pins 4, 9, 10, 11, 12, 13 they are used for the ehternet/SD shield. but that is for a later time.