Mongoose CB 24V450 -Motor Only Range (NiMH)- Pinkerton Park

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knightmb   100 kW

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Post by knightmb » Dec 16 2006 11:18pm

Ok, finally got the fan DC amps figured out. Took me forever to find a piece of wire long enough to actually have some resistance I could measure, LOL.

Each fan uses 2.5 amps @ 12 volts, so basically it's using about 30 watts per fan, all 4 would use 120 watts if connected in parallel.

Now, I think both of these batteries are rated at 5 hours, so 12 AH / 5 = 2.4 amps of current draw for the hour. At 24 volts, that's 2.4 X 24 = 57.6 watts of power the battery should be able to run for the first hour before it's discharged (safety).

Each fan is connected in series, so it's 24 volts / 4 fans so each fan can get 6 volts @ 2.5 amps which means each fan is only "really" using 15 watts of power. 15 watts X 4 fans = 60 watts. Being that the battery is actually pushing out 24 to 26 volts, this brings the watt range to 57.6 to 62.4 watts. Basically means the 4 fans are a good match for a 12 AH battery.

Now, given the run time of the batteries, the NiMH came closes to a "perfect" 12 AH runtime, and the SLA was close behind.

The NiMH is about 98% of it's 12AH rating and the SLA is at about 95% of it's 12AH rating.

Dang, glad I finally got the math right on that one, LOL. Was driving me crazy.

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Elmweaver   10 W

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Post by Elmweaver » Dec 16 2006 11:30pm

The EP12 has a 30 minute rate of 6 amps (12ampdraw). So our battery should be a little less then that, certainly no more then that.

My guess is the fans drew 6.85 amps in the 57 minutes they ran based on the 7.2a/hr rate. Or pretty close to that anyway.

:oops: should have refreshed before I posted. :lol: :lol: :lol:

D-Man   1 MW

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Post by D-Man » Dec 17 2006 12:09pm

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.
Last edited by D-Man on Feb 24 2007 11:58pm, edited 2 times in total.

knightmb   100 kW

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Post by knightmb » Dec 17 2006 12:21pm

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. :lol: :lol: :lol:

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