Build an FTC Battery Load Tester

Load Tester Circuit Diagram

• Batteries used in our robots can always be recharged, but over time, some batteries lose their ability to hold that charge. 
• A voltmeter only shows the current voltage, not capacity. 
• Bad batteries can have a good voltage after charging, but have very limited capacity.
• Load testing quickly indicates whether a battery has lost its capacity to hold a charge.
We have developed a safe, low-cost method of testing the 12 Volt Tetrix batteries used in FTC competitions.  And our load tester found a bad battery that could not have otherwise been detected!
Commercial load-testers for 12 Volt batteries are designed for measuring car batteries, typically applying a 50 amp load or more.  To apply an appropriate load for Tetrix batteries, we used two 50 Watt fog lamps from an auto-parts store.  
Building directions are available in two downloadable formats below: PowerPoint or PDF. Same content.  There is also a file link for the Excel test data and performance graph.
We welcome your feedback and improvement suggestions! Use the Contact link to drop us a line!
Photos and diagrams here are clickable for larger versions.

Voltage vs Time, Tetrix battery under 100 Watt load

Henry Bass,
Apr 21, 2014, 5:03 PM
Henry Bass,
Apr 21, 2014, 5:05 PM
Henry Bass,
Apr 21, 2014, 5:03 PM