Electric AC Cobra (looking to reduce high energy consumption - 489 Wh/mi)

[Galane]

I looked up the CALB Grey Cell Test 01 : Half impulse video. 30 minutes, when are the fireworks?

[samway47]

I have a Chevy s-10, lead sled(4500 lb.) running a 9in. motor. Top end on dc motors are usually around 5500 rpm. Check with Warp, but I think you'll find that you need to run around 4000 rpm and that you are hurting the motor and creating excess heat buy running at low rpms. If you can get your car on a chassis dynomometer you will see exactly where your torque drops off and when to shift.

[RE_Farmer]

Originally Posted by Galane

I looked up the CALB Grey Cell Test 01 : Half impulse video. 30 minutes, when are the fireworks?

IIRC, there are a few sparks near the beginning, but the high amperage and glowing spanner are near the end. Sorry I don't have an exact time stamp (going from memory); I'd just scroll the little preview window on the progress bar at the bottom until you spy the glowing wrench.

[RE_Farmer]

Originally Posted by samway47

I have a Chevy s-10, lead sled(4500 lb.) running a 9in. motor. Top end on dc motors are usually around 5500 rpm. Check with Warp, but I think you'll find that you need to run around 4000 rpm and that you are hurting the motor and creating excess heat buy running at low rpms. If you can get your car on a chassis dynomometer you will see exactly where your torque drops off and when to shift.

Samway, you're right about motor speed and heat. The Warp9 hp peaks ~3500-4000rpm. Yes, series DC motors do make max torque @ 0 rpm, but they also make max heat. One needs to spin these motor up to get rid of the heat AND to clear out the brushes' carbon dust.

There was a guy at EVCCON that trashed his motor. George Hamstra took a look at it and thinks it might have been due to excessive carbon dust shorting the motor. To ameliorate the heat, you need to keep the revs up and, or at least add an external blower to cool the motor at low to zero rpm and clear the brush dust.

[ev99saturn]

NetGain offers the TransWarP motors for two purposes: 1) as a second motor coupled by the driveshaft to a primary motor, and 2) for use in a direct drive car as long as the car is under 2200 lbs. They also recommend that if it is used as direct drive that the motor and controller be sized at twice what would be normally needed for that vehicle.

I agree that the motor is working harder in my car than it would with a transmission, but it still falls within the recommended guidelines from NetGain. The car weighs 1928 lbs. Additionally, there is an external blower that forces more air through the motor to keep it cool at lower speeds.

I don't live in-town, so my driving is almost all 50 mph roads. Once I leave the driveway, there are only two stops/starts then it's 50 mph. At that speed the motor is easily able to self-cool from the internal fan.

So I don't mind pushing the motor a bit harder at startup. I expect that it's reducing my range a little, but the advantages of direct drive over transmission are more important to me. Plus it is somewhat a matter of curiosity to see just how it works out.

So far I am pleased with how it runs, and I attribute most of the high wh/mi to poor aerodynamics and fat tires. These are things that I can improve upon, and have already started to work towards.

For the RPMs, this motor is rated to 5,000 and confirmed a few weeks ago via phone call to the president of NetGain.

Originally Posted by samway47

I have a Chevy s-10, lead sled(4500 lb.) running a 9in. motor. Top end on dc motors are usually around 5500 rpm. Check with Warp, but I think you'll find that you need to run around 4000 rpm and that you are hurting the motor and creating excess heat buy running at low rpms. If you can get your car on a chassis dynomometer you will see exactly where your torque drops off and when to shift.

[ev99saturn]

Carbon dust buildup is a concern for any motor. Potential problems are amplified with higher current. My plan right along has been to finish seating the brushes (only another 100 miles to go), then open the motor and blow out the carbon before cranking up the amp limit to the max.

I have heard that a carbon dust buildup > high current flash-over sounds like a gas car backfire. I'd rather not hear that!

Originally Posted by RE_Farmer

Samway, you're right about motor speed and heat. The Warp9 hp peaks ~3500-4000rpm. Yes, series DC motors do make max torque @ 0 rpm, but they also make max heat. One needs to spin these motor up to get rid of the heat AND to clear out the brushes' carbon dust.

There was a guy at EVCCON that trashed his motor. George Hamstra took a look at it and thinks it might have been due to excessive carbon dust shorting the motor. To ameliorate the heat, you need to keep the revs up and, or at least add an external blower to cool the motor at low to zero rpm and clear the brush dust.

[Galane]

Originally Posted by samway47

I have a Chevy s-10, lead sled(4500 lb.)

Only if you're running batteries containing lead. 'Course LiPo Sled or LIon Sled just don't sound quite right...

[ev99saturn]

How about lipo suckamps?

Originally Posted by Galane

Only if you're running batteries containing lead. 'Course LiPo Sled or LIon Sled just don't sound quite right...

[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

[ev99saturn]

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

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