The following information is for the EMANT300, EMANT380
Question: I have a 6 to 10W solar panel and would like to monitor its output voltage and current. The Voc is 22V and its short circuit current is 0.6A.
WARNING: Note that the max input voltage with respect to GND for the EMANT380 Bluetooth DAQ is 3.3V. For the EMANT300 USB DAQ, the max input voltage with respect to GND is 5V. The min input voltage is the same for both at 0V.
To measure the cell voltage of 22V, we will need to attenuate the voltage to meet the input requirements of the EMANT3X0 modules. For the current measurement, we measure the voltage drop across a sense resistor. A possible schematic is shown below
The voltage at AIN3 is attenuated by 10 for the resistor values given. The voltage equation is
By reading the voltage between AIN3 and AINCOM and multiplying by the attenuating factor of 10, we obtain the solar cell voltage.
The current of the solar cell ICELL is measured using the sense resistor RSENSE. Using a 0.2 ohm sense resistor, the voltage drop across RSENSE at 0.6A is 120mV. In this instance a 0.25W resistor is sufficient.
Applying the same formula to VAIN2 and since R1 = R3 and R2 = R4 and simplifying, we obtain the relation between the measured voltage and the solar cell current.