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

[thomason2wheels]

Originally Posted by nimblemotors

Nice looking car wayne!

500Wh/mi is indeed pretty poor efficiency.
An open-top roadster is horrible for aerodynamics, the rollbar probably makes it even worse, and that big grill opening..

If you get this even at 50mph might have some type of drag going on.
Check the brakes. Check motor for drag.
With fat tires be sure alignment is correct, fully inflate the tires.

There has been a big trend to get a "big block" e-motor to go fast.
An 11" motor is overkill for such a light car.

Whatchu talking about, too much motor is just enough . I bet that sucker is a blast to drive.

[thomason2wheels]

Originally Posted by thomason2wheels

Whatchu talking about, too much motor is just enough . I bet that sucker is a blast to drive.

Ok, now i want to ask a serious question. If the driveline was goin through a 4 or 5 speed tranny, would allowing the motor to turn more rpms in a lower gear reduce the load on the batteries?

[mort]

Originally Posted by madmike8

I think you need a transmission or steeper gears in the rear. Motors are more efficient at higher rpms. Driving at 40-50 your burning more amps since the rpm is around 2k. A transmission would allow you to keep the motor in a more optimal rpm for a given speed.

Actually:

Originally Posted by thomason2wheels

Ok, now i want to ask a serious question. If the driveline was goin through a 4 or 5 speed tranny, would allowing the motor to turn more rpms in a lower gear reduce the load on the batteries?

Yes, but only a little. Any transmission will waste some power. If your first gear is 95% efficient and you get up to the 91% efficient motor rpm then the over-all efficiency in first gear is 86% which is better than the 80 - 85% you'd expect without changing gears.

But imagine a 3:1 first gear, I'd like to have that 180 lb-ft (3 x 60) at 10 mph.
-mort

[Ryland]

My first thought was also that the motor was spinning to slow, but 2,500 RPM is pretty reasonable for 50mph and the motor is over sized for the weight of the car that it's never under a high load so I wouldn't be surprised if it never sees over 200 amps because that motor does just fine with a 4,000 pound vehicle like a pickup truck that also has that kind of drag.

There are some 225/50R17 tires that are also around 805 revs per mile that have low rolling resistance options, I would have to do a little more searching to see if there is slightly wider tire that is a LRR tire, but the load range on a tire like that is still well below the weight of your car that you are not going to be coming even close to pushing the limits of what the tire can handle.
Do you know what brand and model of tire you have on right now? just so we all have a better idea.

[ev99saturn]

I debated a lot about going transmission or direct drive, and decided to try direct drive.

Looking at the fastest EVs out there, NEDRA vehicles, they are mostly direct drive. If the design can stand up to racing, it ought to handle street driving. For normal street driving the big motor is not working that hard and there are some advantages over transmission drives.

This is my second EV build, the first one used a 5 speed transmission. I rarely used 1st or 5th gears.

With direct drive, vs. transmission, there is definitely a higher current demand to start rolling. But, at 50 mph a transmission would be in 4th gear anyway and running at a similar rpm to direct drive.

Originally Posted by madmike8

I think you need a transmission or steeper gears in the rear. Motors are more efficient at higher rpms. Driving at 40-50 your burning more amps since the rpm is around 2k. A transmission would allow you to keep the motor in a more optimal rpm for a given speed.

Btw love the Cobra!

[ev99saturn]

The tires are BF Goodrich g-force Super Sport 245/45 R17 on the front and g-force Drag Radials 315/35 R17 on the rear.

I plan to bring the car to the local drag strip next year, after I have completed building all of the battery packs, and get it up to full power. So the tire choices were with that goal in mind.

A number of people have suggested that with that much power and low weight, getting the rear tires to hook up will be a problem, so I went as wide and sticky as I could.... and helped clobber the range in the process. Everything is a trade-off!

Originally Posted by Ryland

My first thought was also that the motor was spinning to slow, but 2,500 RPM is pretty reasonable for 50mph and the motor is over sized for the weight of the car that it's never under a high load so I wouldn't be surprised if it never sees over 200 amps because that motor does just fine with a 4,000 pound vehicle like a pickup truck that also has that kind of drag.

There are some 225/50R17 tires that are also around 805 revs per mile that have low rolling resistance options, I would have to do a little more searching to see if there is slightly wider tire that is a LRR tire, but the load range on a tire like that is still well below the weight of your car that you are not going to be coming even close to pushing the limits of what the tire can handle.
Do you know what brand and model of tire you have on right now? just so we all have a better idea.

[nimblemotors]

Originally Posted by thomason2wheels

Whatchu talking about, too much motor is just enough . I bet that sucker is a blast to drive.

Exactly what I mean with this trend that "bigger is faster".
The eMotor is more like a gas transmission.
So its more like you put in an extra 200lb 10-speed transmission in your gas car to make it faster, which actually makes it slower because its heavier.

The power in an electric car comes primarily from the batteries and the controller.

[ev99saturn]

A gasoline version of this car weighs about 2200-2300 lbs, 300 lbs heavier than mine is today. When I add the other battery packs it will be almost the same weight as gas.

Yes, it's "all about the batteries" as Bill Dube (owner of the Killacycle) would say. Not all battery choices can deliver high current. The motor can only deliver to the wheels what the batteries can put out. The battery packs in the Cobra are the same chemistry that Bill is using, nanophosphate lithium ion.

Originally Posted by nimblemotors

Exactly what I mean with this trend that "bigger is faster".
The eMotor is more like a gas transmission.
So its more like you put in an extra 200lb 10-speed transmission in your gas car to make it faster, which actually makes it slower because its heavier.

The power in an electric car comes primarily from the batteries and the controller.

[Ryland]

Originally Posted by ev99saturn

The tires are BF Goodrich g-force Super Sport 245/45 R17 on the front and g-force Drag Radials 315/35 R17 on the rear.

I would look around and see if you can find someone with another set of tires that would bolt on so you could try them without spending any money, compare how http://ecomodder.com/forum/showthrea...17s-23509.html found that just changing tires boosted his mileage by over 10mpg or about 20% going for a sticky performance tire to a LRR tire.

[few2many]

Raise your voltage, get a transmission.