So maximum discharge current = 4.2 / 10 = 0.42A = 420mA Multiply 1000 to convert it into milliamperes. Here, V = Voltage across the load resistor and R = 10 Ohm Note: I am assuming the voltage drop across the MOSFET is negligible. So this design can be adapted easily to achieve my goal.Ĭurrent (I) = Voltage ( V ) - Voltage drop across the MOSFET / Resistance (R) The reason is that my future plan is to use the same tester for the multi-chemistry battery. Then you may ask, why I am using two dividers unnecessarily. The output from the divider is connected to Arduino analog pin A0 and A1.Īrduino analog pin can measure voltage up to 5V, in our case the maximum voltage is 4.2V (fully charged). It consists of two resistors with values 10k each. The voltages are measured by using two voltage divider circuits. We have to find the voltage across the load resistor. ![]() Multiplied this by the time to obtain the milliamp-hour ( capacity ) value. Arduino measures the voltage across the load resistor and then divided by the resistance to find out the discharge current. This discharges the battery over a period of time. It allows current to pass from the positive terminal of the battery, through the resistor, and the MOSFET then completes the path back to the negative terminal. The function of the MOSFET is to connect or disconnect the load resistance with the battery.Īrduino checks the battery condition, if the battery is good, give the command to switch ON the MOSFET. Two voltage dividers circuit is used to monitor the voltages across the load resistance. A buzzer is used for giving different alerts. An OLED display is used to display the battery parameters.3 screw terminals are used for connecting battery and the load resistance. The design is very simple which is based on Arduino Nano. In the actual board, they are inside but in the schematic, they are lying outside. The only exceptions are the buzzer and OLED display. ![]() The positions of the components and wiring are similar to my actual board. To understand the schematic easily, I have drawn it on a perforated board also. Please do not attempt this if you are a novice. This tutorial was written for those who have knowledge of rechargeable lithium-ion technology. I cannot be held responsible for any loss of property, damage, or loss of life if it comes to that. Note: Please dispose of the bad batteries properly.ĭisclaimer: Please note that you are working with a Li-Ion battery which is highly explosive and dangerous. I hope this little tester will be useful, so I am sharing it with you all. But for the time being, I am happy with it. In the future, I will try to implement those things. The accuracy of the tester won’t be 100% perfect, but it does give reasonable results that can be used and compared with other batteries, so you can easily identify good cells in an old battery pack.ĭuring my work, I realized, that there are a lot of things that can be improved. This version is a really simple one, which is based on Ohms Law. If you enjoy my work here on Instructables, consider joining my Patreon, it will be a great help for me to make more interesting projects in the future.Ī few weeks ago, I have started the project from the basics. So I really wanted a way to measure each cell's exact capacity instead of their voltages. ![]() ![]() Earlier in one of my Power Bank Instructable, I told, you how to identify good cells by measuring their voltages, but this method is not at all reliable. It is very difficult to identify the good cells in the battery pack. I have salvaged so many old lap-top batteries ( 18650 ) to reuse them in my solar projects.
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