Simple Characterization Circuit for Rechargeable AA Cells


Posted on Feb 4, 2014

This characterization circuit, plus a PC and some software, accurately measures the full discharge cycle for a rechargeable AA cell. Cell capacity and output resistance can easily be determined from the curve resulting from these measurements. Rechargeable AA cells are very popular for a large variety of portable applications. The number


Simple Characterization Circuit for Rechargeable AA Cells
Click here to download the full size of the above Circuit.

of brands is also high and the cell quality can differ considerably. Cell capacity is sometimes different from that specified, and the capacity often deteriorates dramatically after a limited number of discharge cycles. The proposed characterization circuit, in combination with a PC and AA-Cell Characterizer software, can accurately measure a full discharge cycle. From the resulting curve you can easily determine the cell capacity and output resistance. The circuit is built around an IC intended for fuel-gauging applications in battery packs ( DS2756 ). The DS2756 provides the key components necessary to accurately estimate remaining battery-pack capacity by integrating low-power precision measurements of temperature, voltage, current, and current accumulation (integral of current). This hardware can also record the discharge cycle of a single AA cell (either NiCd or NiMH ) with accuracy. In Figure 1, the simple circuit is connected to the USB port of a PC. No external power source is required because power is extracted from the USB bus voltage. U1 ( DS9490R ) is a USB dongle that converts the USB protocol to the 1-Wire ® protocol, thereby allowing the PC to communicate with the key circuit component (U2). U2 measures the cell voltage on pin 1 (VIN) through R1, the cell current through R4, a 25m © sense resistor connected to pins 7 (SNS) and 2 (VSS). The programmable I/O at pin 3 (PIO) allows PC software to control the gate...




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