FEZ Accu Test: description

Introduction

I designed a simple testing device where you have to insert fully charged batteries (my device has no charging capabilities!). These batteries will be discharged over a period of 8 hour during which the voltage of each battery is measured once a minute. After the eight hours the data is written to a .CSV file which can be opened with Microsoft Excel.

The device involves two parts: some self designed hardware and a processing unit. I have chosen to use my FEZ Panda for the processing unit: it will control my own hardware and interpret the measurements. The nice thing is you can replace it with something else like a K8000, a microcontroller, ...

Testing Procedure

As you could read earlier the batteries are checked for a period of 8 hours. Each minute the measured voltage (mV) is written to the memory which is saved as a .CSV file after the completion of the test.

During the test each battery will be discharged with a current of 150 to 200 mA. This causes the batteries to drop their output voltages slowly. It is this voltage drop that is monitored during the 8 hour period.

Every 15 minutes the discharging will be stopped for a while: this allows my tester to measure unloaded voltage, which is usually higher than the loaded output voltage. You sometimes can find bad batteries by comparing these values.

This device can only test signle AA cells with a voltage of 1.5 V! You cannot use it to test battery packs where multiple cells are placed in series.

Ignoring this restriction will cause a high current through the control FETs. If the current rises above the limit of 500 mA the FETs will overheat.