D-Man wrote:If the fan's put out 10 amps total and the Nimh lasted 1 hour, doesn't that equal a capacity of 10AH ? A loss of 2 AH. A 17% loss in capacity.
The batteries are rated at the 5 hour C, so that means they can do 12 amps in 5 hours. When you discharge the battery in 1 hour instead of 5, you have to divide it out, so it ends up actually be 12 /5 = 2.4 AH for the one hour. Since each fan used 2.5 amps @ 12 volts to run, they are very close to what a 12AH battery can handle in terms of current drain for the one hour. But, the only problem is, the battery is 24 volts, so that means you need more fans to even out the drain for the hour. So if you take that each fan uses 12 volts @ 2.5 amps, each fan can in theory use 30 watts of power. Given that means the 24 volt battery @ 2.4 amps can produce in theory 57.6 watts for the entire hour, two fans should be enough (hooked in parallel) to give it a good test. But you know me, I like experiments that are over-complicated. I had 4 fans and wanted to run them all at once. The problem is, they draw too much power in a parallel configuration for this test. So by putting the fans in series, the voltage drop across all of them is divided by 4 from the 24 volts to give each fan 6 volts @ 2.5 amps that they use. Multiple that out and you get 6 X 2.5 = 15 watts per fan. Multiple that by the 4 fan and you get 15 X 4 = 60 watts. A tad bit over what the battery can do in theory, but close enough for a one hour test.
Another reason I used 4 fans instead of 2 is because at 12 volts and 2.5 amps, they almost fly away on their own. With 4 fans, the reduced voltage lowers the speed so that they stay put on the table in the pictures.