| Tester for Smart Battery Chargers |
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We needed a method of production testing the fast lithium ion battery chargers that we had designed for a customer. The test method for the initial batch used two batteries in different stages of charge to fully check charger functionality. As we had to take one of the batteries over the charge termination point, then discharge it before testing the next charger, this was a time consuming business. A complete test system was designed and built to speed up the procedure.
The system uses a proprietory multifunction board in a personal computer. A battery simulator capable of sinking or sourcing 5 amps and a bespoke interface board were designed and assembled. Power to the charger goes via current measure circuits on the interface board. An empty battery case was modified and when it is inserted into the charger, it allows power and control signals to be intercepted by the interface board. The charger is normally controlled by the SMBus driven by the smart battery. We use a separate SMBus interface board and computer program to send signals to the charger. A test program was written using LabWindows/CVI to control the tester.
This screen capture shows the control and indication functions for rapid manual testing. The tester is controlled by the buttons at the bottom of the screen, the simulator voltage and current limit by the controls at the top. Supply and battery voltages and current are shown in real time on the screen. A log file is created for each charger and each test is quickly set up and a single button press records the test parameters and results. These are exported to a spreadsheet for analysis and printing.
The interface board shown here is designed for full automatic testing of the battery charger. The battery simulator can also be used with an adapted charger to do the initial cycling of the batteries to allow them to be conditioned so that the gas gauge learns the battery capacity. |
