1/30/2024 0 Comments Battery monitor circuits![]() All images and diagrams courtesy of yours truly.In the next page, we will examine the contruction and components of the circuit.Ĭontinue on to Battery Monitoring Circuit components and layout. In this project, an additional program is written for a separate PIC MCU to simulate the requesting of battery data from the BMC. The circuit was designed to keep the output voltage below 1.2V for a 1A load current and 5.5V battery voltage. This process is interrupt driven and triggered by an i2c "START" condition sent by the external device. Figure 3 shows a high-side battery-current-sensing circuit using the TLV369, which features a rail-to-rail input stage with >100dB of CMRR over the full supply voltage range. Once the cell voltages are determined by the BMC, they will be read by external devices via the i2c protocol. Therefore the microcontroller ADC results from each cell will be scaled to reflect a range of values from 3.0-4.2 V.Ĭommunication between battery monitor and external MCU: For LiPo battery chemistry, it is important to not allow any individual cell to drop below 3.0 per cell (for both battery life and safety reasons). The resulting output of these differences will be sent to 4 analog input pins of a PIC microcontroller and measured against a reference voltage of 4.2V (4.2V is the maximum cell voltage for LiPo batteries). Our sampling technique wil involve using differential amplifiers (configured as subtractors) to measure the difference in voltage levels between each wire of the connector and the wire that proceeds it (in order of the series connection). Working of the circuit is based on the base biasing of transistor T1. It is an ideal add on circuit to monitor the charge level in 12 volt miniature batteries used in Portable devices or Alarm systems. For purposes of illustration, if we assume that the pack is at its nominal voltage, the wires of the JST-XH connector will have the following voltages values (with respect to ground of our monitoring circuit):įrom observation (and by measuring the voltages of each cell with respect to the black wire) you will notice that the individual cells are connected in series. This simple Battery Monitor lights an LED when the battery voltage drops below 9 volts. This means that each cell (there are 4 cells in a 4S pack) will measure a nominal 3.7 volts. ![]() Using the battery shown above as an example, we see that the nominal voltage of the pack is 14.8 volts. This reference voltage will be connected to ground of the BMC. The black wire is connected to the negative terminal of cell #1 of the battery pack. Our primary method of doing this will be through differential amplifiers connected to the 5-pin JST-XH connector of the battery. Our goal here is to design a Battery Monitoring Circuit (BMC) that can sample the voltage of the individual cells in a 4s LiPo battery such as the one found here. Adjust the potentiometer till LED 2 start to glow.Four Cell LiPo Battery Monitoring Circuit Adjust potentiometer till LED 1 start to glow.įor over charged voltage calibration connect the variable DC power supply in place of battery and set voltage to 14.4V. ![]() For under charge voltage calibration connect the variable DC power supply in place of battery and set voltage to 11.3V. Wire up the entire circuit component as shown in circuit diagram. The charge of the battery continues as it hits the least preset level of 11.3V as set in the circuit and LED 1 glows to verify the low-level status. If LED is off the normal charging of the battery is ensured. Turning the switch off helps to protect the battery from overheating. Thus, LED 2 is used to indicate over charge voltage situation. When battery voltage reaches higher then predetermined value LED 2 start to glow. Similarly, VR 2 is used to adjust the higher voltage of battery. Thus, LED 1 is used to indicate under charge voltage situation. When battery voltage reaches lower then predetermined value LED 1 start to glow. Potentiometer VR 1 is used to adjust the lower voltage of battery. The zener diode connected in the circuit is in reverse mode in order to produce regulated output of 3.6V. Check the polarity properly while making connections with the 12V battery. The level monitoring circuit is fixed to the battery as shown in circuit. The status of batteries also needs to be monitored constantly, This, circuit does the job. The main components of Battery State Indicator circuit are three low power general purpose transistor 2N2222. The circuit of Battery Status Indicator Capacitor is shown in figure 1. Circuit Description of Battery Status Indicator
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