Keith, I had a long debate about transmission or not. Yes, the car pulls more current to start, but almost all of my driving will be on 50 mph roads.
Part of the strain on my pack now is due to the fact that it's still low voltage, with the remaining packs under construction. So it takes more battery amps now than it will at the much higher voltage. The pack is only 119V now and will increase to 320V.
The battery amps when accelerating easily is still only double digits to maybe 20 or 25 mph, where the motor is already pulling 200-300 amps. Once the car gets up to 50, then the aero and rolling resistance becomes the big culprit in power consumption.
The car is under 2000 lbs, so should be as low as 200 wh/mi, but instead is north of 400. My Saturn EV was 3,000 lbs but pulled only about 80-100 amps at 50 mph. The Cobra is pulling 150-200A at 50 mph.
The larger issues are rolling resistance of the fat tires, and terrible aerodynamics of the car's shape. These two thing are being addressed and I am hoping for a decent improvement there. Jack Rickard build an electric Cobra too, and simply by changing from drag radials to lower rolling resistance tires, he reduced the car to below 300 wh/mi. I'm hoping that my planned aero improvements and some LLR tires will get the car well below 300 wh/mi.
The primary intent of this car is plain old driving fun, but also acceleration performance. The single speed helps with acceleration because there is no need to waste time shifting gears. It works very well for NEDRA, so I decided to give it a try too.
My experience with a previous EV conversion is that 1st gear is not worth using. I always started in second gear. First gear was just too torquey and jumpy, even in a Saturn sedan with a lowly 85 hp electric drive.
Wayne
Quote:
Originally Posted by kstegath
Hi Wayne,
Put a transmission in your car. Even though you can run the motor direct drive (4:1 differential), generally speaking, the lower the motor's rpm, the higher its current draw. High current gives great acceleration, and high voltage gives higher RPM, but current kills your batteries and your range. With direct drive, from a dead stop, you're pulling a lot of current to get your car moving. The 4:1 differential is great if you have a transmission and use 1st and second gear.
Keith
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