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Battery (Lithium, NiMH, NiCd) Capacity Tester Using Arduino

The increased interest in IoT and electric automobiles around the world is driving an increase in the use of Lithium-Ion/Lithium-Polymer/NiCd/NiMH batteries as more devices and applications are using them, due to their high energy storage capacity to size ratio. This increased interest is, however, causing an increase in the number of batteries with “fake” ampere-hours ratings in the market. These fake ratings could lead to the failure of several projects, especially IoT projects in which developers factor in the Battery ratings in their On-time calculations. As such, to find a way of mitigating the failure-risks this problem poses, for today’s tutorial, we are going to build a battery capacity tester which can be used to get the correct energy storage capacity of any Lithium-Ion/Lithium-Polymer/NiCd/NiMH batteries (with voltage below <5v).

There are quite a number of battery testing projects on the internet, each with a different approach, but for today’s tutorial we will be chronicling the efforts of Instructables user: Sam Moshiri, due to the quality of his build and its standalone and compact nature. The goal of the project according to him was to build a compact, easy-to-build device, capable of measuring the capacity of almost any kind of battery (< 5V) using an adjustable constant load setup with an LCD on which the capacity of the battery is displayed.

The idea behind the constant load current setup is simple. If you draw a constant current from a battery over a particular period of time, you will be able to calculate the true ampere-hour capacity of the battery based on the amount of voltage that was dropped during that time. To achieve the constant load current, a resistor network with an LM358 operation amplifier and a MOSFET was used. The setup has two push buttons (+ and -) that allow users to set the load current before the process starts, and a third push-button to reset the board when it’s time to test another battery. The Battery’s voltage is fed into one of the analog pins on an Arduino Nano which monitors the voltage drop based on the preset current draw, calculates the battery capacity, and displays it on a 16×2 LCD Display.

At the end of this tutorial, you would know not only how to determine the battery capacity, but also how to design for constant load / constant current draw and use a 16×2 LCD display with the Arduino.”

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