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Old 05-26-2012, 01:31 PM   #16 (permalink)
Electric MG Midget
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Originally Posted by rmay635703 View Post
I disagree, a DIY EV for the purpose of saving money and not creating a money hole is best operating at a LOWER voltage at LOWER amps using more or less common off the shelf parts.

Every EV I have dealt with runs most efficiently (in terms of power in power out) with the pedal at WOT. AC systems and DC systems become rather inefficient at low throttle positions, enough that on a lithium setup you are loosing at least 25% out the window on PWM if you drive in that region often with a typical controller.


I found your reply interesting. In particular your claim about 25% loss in efficiency when not operating at WOT. My controller, and I've seen others claim 98% efficiency. Since they use PWM to get that, I'm interested in why you think it is only 75% , not the 98%.
I would agree that picking a gearing that allows for using one gear and eliminating transmission losses is a good idea. In my 4 speed transmission, the 4th speed is straight through, so It doesn't have losses due to gear friction, but I do have losses due to the transmission oil in any gear. I drive in 4th gear whenever I can.
Since we're on the topic of efficiency I wanted point out that fast acceleration to a given speed doesn't use any more energy than getting there slower. The energy is the same, but the power required is higher. I haven't tried bringing this idea up yet because I thought it might cause some controversy. For electrics the only extra losses would be from I^2 R losses due to needing extra current, and the purcket effect which for Lithiums isn't very much. I donít know how much the I^2 R losses are, so Iím going out on a limb as far as that is concerned.
Frank '77 Electric MG Midget
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