The complete circuit diagram for monitoring Multicell voltage in Lithium Battery Pack is given below. We have not used an op-amp for the 1 st cell since it could be measured directly. Similarly the Op-amp O2 and O3 measures the 3 rd and 4 th cell voltage respectively. The first op-amp O1 measures the voltage of the 2 nd cell by calculating the difference between 2 nd cell terminal and 1 st cell terminal that is (8-4). Note that this image is only for representation the actual circuit needs more components and will be discussed later in this article. So for our purpose of measuring 4 cell voltages we need three differential op-amps as shown below. We already know an Op-Amp when working as a differential amplifier gives the difference between the two voltage values provided to its inverting and non-inverting pin. Hence in this tutorial we will use the Op-Amp Differential Circuit to measure the difference between each cell terminals to measure individual voltage.ĭifferential Circuit to measure individual Cell voltage At crude way is to use a potential divider to map down the voltage levels and then measure them, but this method will reduce the resolution of the read value to more than 0.1V. So we need to introduce some extra circuit here which could help us measure the individual voltages. This is because the reference point cannot be changed from ground. But, for the other cells we have to measure the voltage of that cell along with the previous cells, for instance when we measure the voltage of 4th cell we will measure the voltage of all four cells together. Now if we use a microcontroller like Arduino to measure the cell voltage, we will have no problem in measuring the voltage of 1 st cell since it has the other end connected to ground. The below picture illustrates the sameįor simplicity let us assume that all four cells are at a voltage level of 4V as shown above. The problem with measuring individual cell voltage in a pack of series connected battery is that, the reference point remains the same. Measuring Individual Cell Voltage in a Series Battery Stack For the sake of this project we will use four lithium 18650 cells connected in series to form a battery pack and design a simple circuit using op-amps to measure the individual cell voltages and display it on a LCD screen using Arduino. In this article we will learn how we can measure the individual cell voltage of the cells used in a Lithium battery pack. So measuring the voltage and current of cell is vital for any BMS circuit, be it a simple power bank or laptop battery or as complicated pack as EV/Solar batteries. Only with these two values the BMS could calculate the SOC or SOH and perform cell balancing etc. This is done by measuring the voltage and current (sometimes temperature also) of the cells in the pack. To do anything, the first step for the BMS would be to know the current status of the cells in the Lithium battery pack. We have already learnt enough of it in this Battery Management System article, so check them out if you are new here. A BMS is a sophisticated unit in an EV which does a lot of activity like monitoring the cells, balancing them and even protecting them from temperature changes. To maintain the battery pack in full health is the responsibility of the Battery Management System (BMS). The mileage and performance of an Electric Vehicle depends on the capacity and efficiency of its Battery Pack.
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