Quote:
Originally Posted by Jon Stratis
Ether - That sounds like an excellent test. It looks like radio shack has some 1 ohm resistors in stock in the area, so I can pick some up before our next meeting and challenge my students to figure out how to design a test to determine the rate of discharge if we hadn't added the relays (all of the students who built the cart and helped solve the problem initially have graduated, so this will be a great excuse to transfer that knowledge forward to new students!). Of course, the solution is pretty straightforward (use the resistor to bridge the terminals on the relay, measure the voltage drop across the resistor)... I just hope none of them are following this thread, or they'll come with the answer too easily!
Expect answers in a week... our next meeting is Monday night.
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Results: We used a 1 ohm resistor (verified by two multimeters). The battery, while connected to the charger (which was unplugged), was measured at 12.811 V. The resistance across the shunt resistor measured 0.002 V with one multimeter, and 1.2 mV with the second.
I have my students do the math at the meeting tonight... I'll hold off in case any enterprising students watching this want to do the math too!
That'll teach me to send anyone for a tool. - Rich Kressly [more] 
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