Quote:
Originally Posted by IndySam
CBAIII is a must have for every team.
We also use it to load test our Vex batteries.
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Buying a product like this is a great idea if you have the money. But, with our team being on a shoe string budget we decided to build our own battery tester out of scrap parts. Initially it was not much more than some homemade high power resistors that could be used to load the battery while you read the voltage with a hand held voltmeter.
The resistors for our tester were just lengths of coiled nichrome wire salvaged from a scrap electric heater. We cut the length of the coils to give us the highest current draw that did not overheat the wire, and then doubled up several lengths in parallel to provide a heavy load test. We wanted to draw enough current for a long enough period that we adequately simulated a real match.
Later we added some fans, and a solenoid controlled by digital I/O and an analog input so we could start and stop the test and read voltages from a computer. Not exactly portable, and not constant current, but most of the parts were already in hand. Also, our software team wrote a program to control the test and plot out the voltage drop over time. We can run tests of varying length to give a quick analysis of a battery, to watch for a sudden drop off in voltage during a longer test to simulate a real competition. The plot shows unloaded voltage, loaded voltage, voltage drop over time, and voltage recovery.
If we did not have some of the parts around already, building something like this would probably be more expensive than just buying a ready made unit.
And after seeing the comments here, we should probably try to buy a real load tester next season. But for now the home brew one works for us and seems to impress the kids with what you can do yourself without a lot of parts when you have to. Remember the old Yankee saying.
Use it up, wear it out,
Make it do, or do without.
Tom