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Old 11-26-2007, 12:57 PM   #223 (permalink)
MetroMPG
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Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 53.56 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 61.46 mpg (US)
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01-08-2007, 01:44 Pm

Dax, the current limit of the golf cart controller is 275 A. And that value drops as it heats up from max duty cycle - 275 A is its 2 minute rating; 200 A = 5 min; 125 A = 1 hr.

(EDIT: and it was in 2nd - but I didn't have it "wide open" I would say 1/3 to 1/2 on the pot).

The forklift controller limit is in the neighbourhood of 400A, but it also has a bypass, which will feed full battery current to the motor under certain (logic) conditions.

So with the golf cart controller at 36V, we're limited to the equivalent of 275 A * 36 V / 746 W/HP = 13.3 HP. At 48 V we'd get 17.7 hp. (Not counting losses.)

EDIT: aw, what the heck - let's throw in some loss estimates too. PWM controllers are typically described as "above 90% efficient", and the motor may be 75% efficient. So now we're down to:

HP (golf cart controller @ 36v) = 13.3 * .9 * .75 = 9.0 HP
HP (golf cart controller @ 48v) = 17.7 * .9 * .75 = 12.0 HP

Still, 9 HP is theoretically enough to go 55 mph in this car on level ground (assuming you don't run out of power before you eventually accelerate to that speed). What else am I missing?
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