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

[Patrick]

What size wire are you using? You might have some losses there, especially at 1400 amps. Increasing the wire size might help, but will add some weight to the car so there is a point of diminishing returns. Also, try to keep the wire runs as short as possible.

[allen_dodge]

Hmm, I'm intrigued by the thought of not having a penalty for accelerating rapidly, if this is true then it might actually be more efficient to reach cruising speeds sooner, but as you say more data will tell. I really hope this is the case, that makes the dream of owning an electric sports car that much more desirable. I saw a $250,000 electric supercar called the Lightning GT, it was AWD with a motor directly driving each wheel so the drivetrain losses were negligible, combined with very low COD gave it a 200 mile range on 36 KwH worth of batteries, or about the equivalent energy in a gallon of gas. It sounds like you can have your cake and eat it too, but apparently only with electric.

[allen_dodge]

Also, speaking of RC, anyone here ever seen silver windings on a motor before? The resistance is significantly lower, and dissipates heat much better than copper. That should mean even less of a penalty, if any, for high amp draw. I've seen 1:28th scale RC cars (xmods, mini-z) that have silver wound 130-sized motors that would run 60 mph actual speed, where a copper wound motor with the same setup would struggle to break 45.

[allen_dodge]

by the way, the Lightning GT I mentioned above can charge to 80% in less than 5 minutes if you have access to 3-phase 440 volt power. What is the charging time on your lithium batteries?

[ev99saturn]

The high power wiring (battery to controller to motor) is all 4/0 gauge and the runs lengths are minimal. All of the batteries are in the front now, but 3 additional packs will go in the gas tank area over the winter and will require the longest 4/0 runs in the car.

Originally Posted by Patrick

What size wire are you using? You might have some losses there, especially at 1400 amps. Increasing the wire size might help, but will add some weight to the car so there is a point of diminishing returns. Also, try to keep the wire runs as short as possible.

[ev99saturn]

I am charging at 110V with only 15A, so it's 3-4 hours to recharge from a 60% DOD pack. I have read, but not confirmed that these cells can be charged to 80% in 12 minutes, but that would take at least a Level 3 charging station to supply that much current.

Originally Posted by allen_dodge

by the way, the Lightning GT I mentioned above can charge to 80% in less than 5 minutes if you have access to 3-phase 440 volt power. What is the charging time on your lithium batteries?

[allen_dodge]

wow, 12 minutes is still impressive in my book, as a rule of thumb that should also mean that the packs can discharge efficiently. I'm afraid to ask, but how much would your batteries cost by themselves?

[ev99saturn]

After extensive testing on individual cells and then in a small pack, they can discharge like a fire hose. Each cell is about 19.6Ah, 3.3V and about 1 lb. In my testing, they were able to sustain a 370A (19C) discharge with only 22% sag. They are rated to 30C discharge.

During that discharge level, my test load was underwater to keep it cool, and it started boiling water in a second or two. After 20 seconds, the test pack had barely risen in temperature. Seems efficient to me :-)

The cell costs were slightly higher than the more popular (and available) Thunder Sky, Calb, etc cells.

Originally Posted by allen_dodge

wow, 12 minutes is still impressive in my book, as a rule of thumb that should also mean that the packs can discharge efficiently. I'm afraid to ask, but how much would your batteries cost by themselves?

[ev99saturn]

After a few log entries and some BMS adjustments, some gains already appearing.

Logs are here: 2010 Factory Five Racing Mk4 Gas Mileage (DC Cobra) - EcoModder.com

The second and third test runs confirmed the first and were even higher, above 500 wh/mi.

On the fourth measured run, I drafted a trailer for about 3 miles, and got down below 400 wh/mi for the first time. Certainly some confirmation of air drag being significant.

The 5th drive included a long big hill and no drafting. The 423 wh/mi drive was only influenced by reduced pack balancing (mouse clicks) after the charge completed.

One last observation, on the way back down the big hill, with no throttle and coasting about 50 mph, the car either held it's speed or slowed slightly. My previous EV, a Saturn would definitely accelerate while coasting down that same hill with no throttle and starting at 50. More confirmation of drag...

[hamsterpower]

A little late to the thread here. I know you said you had an alignment, but was it aligned for handling or efficiency? There is a big difference. I also really think you need some narrower, harder tires for the rear. Drag radials are way to sticky.