Battery Board
Battery board that connects to the Arduino Controller board.
Two of these can be connected to each controller allowing 8x 18650 batteries to be tested independently.
Each board has 4x identical channels. For each channel:
CHG input is a 4.2V reference from the control board which sets the max terminal voltage of the cell. The 'A' op-amp regulates the voltage to the battery by adjusting the gate drive of the MOSFET. The series resistor provides a crude current limit during charging.
The 0 Ohm resistor allows the PCB layout to be easily customised to allow the op-amp inverting input to be connected at the battery terminal rather than into a generic power plane.
The PNP transistor turns on when the base-emitter voltage is 0.65V. This is true until the current through the upper series resistor is less than ~ 60mA. When the current drops to this point the PNP turns off causing the SENSE voltage to drop to 0V.
DISCHR connection is the logic high output from the control board that enables the constant current discharge circuit. When the logic input is low the discharger is disabled. When the logic input is high the 'B' op-amp regulates the voltage across the lower series resistor to be ~1V. 1V across the series resistor sets the current through the resistor to be a constant 100mA. The potentiometer allows trimming of the current.
The Arduino times how long it takes for the battery voltage to fall to the end of discharge voltage. The time (in hours) x constant current (in mA) gives the battery capacity (in mAh).
Battery Board
Battery board that connects to the Arduino Controller board.
Two of these can be connected to each controller allowing 8x 18650 batteries to be tested independently.
Each board has 4x identical channels. For each channel:
CHG input is a 4.2V reference from the control board which sets the max terminal voltage of the cell. The 'A' op-amp regulates the voltage to the battery by adjusting the gate drive of the MOSFET. The series resistor provides a crude current limit during charging.
The 0 Ohm resistor allows the PCB layout to be easily customised to allow the op-amp inverting input to be connected at the battery terminal rather than into a generic power plane.
The PNP transistor turns on when the base-emitter voltage is 0.65V. This is true until the current through the upper series resistor is less than ~ 60mA. When the current drops to this point the PNP turns off causing the SENSE voltage to drop to 0V.
DISCHR connection is the logic high output from the control board that enables the constant current discharge circuit. When the logic input is low the discharger is disabled. When the logic input is high the 'B' op-amp regulates the voltage across the lower series resistor to be ~1V. 1V across the series resistor sets the current through the resistor to be a constant 100mA. The potentiometer allows trimming of the current.
The Arduino times how long it takes for the battery voltage to fall to the end of discharge voltage. The time (in hours) x constant current (in mA) gives the battery capacity (in mAh).