First Full Range Test of Nissan LEAF Yields 116.1 Mile

[DeaneG]

I was trying to estimate a range reduction vs. speed for various levels of A/C or heater usage. I wouldn't read too much into the "max range" prediction the math also produces, but I think the range reduction vs speed for different climate control power usage numbers have a good chance of being in the ballpark:

http://www.mynissanleaf.com/viewtopic.php?f=4&t=1568&start=38

I can upload the spreadsheet to Google Docs if someone wants to mess with it.

 

[DaveEV]

Link ? I've not seen them.

I doubt anyone other than Nissan can actually calculate that at this point ...

I haven't seen his actual calculations, but the curves should be similar to the Tesla Roadsters.

http://www.mynissanleaf.com/viewtopic.php?p=31036#p31036

http://www.teslamotors.com/blog/roadster-efficiency-and-range

Tesla Roadster's max range is over 400 miles (60% over EPA rating) at a constant 20 mph.

 

[evnow]

I haven't seen his actual calculations, but the curves should be similar to the Tesla Roadsters.

Can't use Tesla's curves directly. cd, area, weight etc etc are all different.

See the long thread by timehorse on trying to derive the range based on equations.

http://www.mynissanleaf.com/viewtopic.php?f=8&t=362&start=10&hilit=la04

 

[DeaneG]

I just used three coefficients for fixed power draw, linear with speed (frictional), and squared with speed (wind resistance). I should also put in a loading-efficiency curve for the motor. But, we'll have our cars soon enough, and can compare experiences then.

 

[jrhubott]

Please post the spreadsheet to Google documents if you don't mind. I've been thinking of putting one together also but it sounds like you have a good start on one.

 

[DeaneG]

Please post the spreadsheet to Google documents if you don't mind..

Here it is:
https://spreadsheets.google.com/ccc?key=0AqNQgsyTlAcLdFAxZ2h4aWNjTTg0ZkdqU1hwU2pvREE&hl=en&authkey=CNmBvqkD

You can probably improve the two kW-vs-speed constants to better align line the range prediction at 0kW climate control usage to the several data points earlier in this thread. I didn't put in an adjustment for motor efficiency vs load - this would reduce range at low speeds where frictional and air drag losses are low.

One big unknown is how much climate control power to ask for - I changed the entry to 1 and 2 kW to see the difference it made. But what is 1kW? An 85 degree day?

 

[evnow]

But, we'll have our cars soon enough, and can compare experiences then.

Right. The 38mph I quoted is from Nissan. Not sure whether it is simulated or real.

 

[tps]

I just used three coefficients for fixed power draw, linear with speed (frictional), and squared with speed (wind resistance). I should also put in a loading-efficiency curve for the motor. But, we'll have our cars soon enough, and can compare experiences then.

Isn't the drag caused by wind resistance the cube of velocity?

 

[tps]

I just used three coefficients for fixed power draw, linear with speed (frictional), and squared with speed (wind resistance). I should also put in a loading-efficiency curve for the motor. But, we'll have our cars soon enough, and can compare experiences then.

The energy (kwh) increases as the square of the velocity, the power required increases as the cube of the velocity. We should ensure that we don't intermix power and energy without the appropriate conversion for time...

 

[DeaneG]

...the power required increases as the cube of the velocity..

Right, energy consumption per mile due to wind resistance is related to velocity squared. Energy consumption per unit time (power) would have a cube relationship.

 

[rmay635703]

Another point is that the controller that drives the AC motor becomes inefficient at low loads.

I think what I would like to see is a motor/controller efficiency chart with the ideal Load for the RPM. This would indirectly give you an ideal throttle position at different speeds.

My guess is even on (at least an AC powered) electric car a point comes where you are better off doing P&G because of controller losses becoming large at low speed.

Another thing not mentioned here is tire inflation, LRR and potentially minor eco mods to the car and their respective effects.

Especiall at low speeds tire resistance is very important, running rock hard tires can net excellent efficiency increases.

Cheers
Ryan

 

[TomT]

The controller uses Pulse Width Modulation and variable frequency so it should not be that much less efficient at light loads and slow speeds.

Another point is that the controller that drives the AC motor becomes inefficient at low loads.

 

[EVDRIVER]

Another point is that the controller that drives the AC motor becomes inefficient at low loads.

I think what I would like to see is a motor/controller efficiency chart with the ideal Load for the RPM. This would indirectly give you an ideal throttle position at different speeds.

My guess is even on (at least an AC powered) electric car a point comes where you are better off doing P&G because of controller losses becoming large at low speed.

Another thing not mentioned here is tire inflation, LRR and potentially minor eco mods to the car and their respective effects.

Especiall at low speeds tire resistance is very important, running rock hard tires can net excellent efficiency increases.

Cheers
Ryan

Rock hard tires also further decrease traction and stopping distance as well as lateral traction even further.

 

[DaveEV]

Rock hard tires also further decrease traction and stopping distance as well as lateral traction even further.

The correct answer is - it depends on your definition of "rock hard".

Stock tire pressures are usually way too low for optimal handling performance. Most people feel that pressures of 40 psi+ start getting into the range of "rock hard" as you feel lot more of the road at those pressures.

Braking performance is not affected much by tire pressures unless they are very low (less than 20 psi). At high tire pressures you'd have to be exceeding the pressure listed on the tire's sidewall to significantly affect braking distance (typically around 45-50 psi).

As far as cornering, higher tire pressures are preferred as well as it keeps the tire from folding over under lateral forces thus keeping more rubber on the road. If you go too far - yes - you'll also eventually reduce traction but again you'd have to be exceeding the pressures on the side wall (typically around 45-50 psi).

Coincidentally, once you've inflated your tires to 40 psi or so you typically hit the point of diminishing returns in terms of reducing rolling resistance - so there's not much point in going significantly higher, anyway.

Conclusion: Increasing tire pressure above the stock 32 psi to 40 psi+ will result in lower energy consumption, better handling and same braking performance at the expense of some ride quality.

 

[EVDRIVER]

Rock hard tires also further decrease traction and stopping distance as well as lateral traction even further.

The correct answer is - it depends on your definition of "rock hard".

Stock tire pressures are usually way too low for optimal handling performance. Most people feel that pressures of 40 psi+ start getting into the range of "rock hard" as you feel lot more of the road at those pressures.

Braking performance is not affected much by tire pressures unless they are very low (less than 20 psi). At high tire pressures you'd have to be exceeding the pressure listed on the tire's sidewall to significantly affect braking distance (typically around 45-50 psi).

As far as cornering, higher tire pressures are preferred as well as it keeps the tire from folding over under lateral forces thus keeping more rubber on the road. If you go too far - yes - you'll also eventually reduce traction but again you'd have to be exceeding the pressures on the side wall (typically around 45-50 psi).

Coincidentally, once you've inflated your tires to 40 psi or so you typically hit the point of diminishing returns in terms of reducing rolling resistance - so there's not much point in going significantly higher, anyway.

Conclusion: Increasing tire pressure above the stock 32 psi to 40 psi+ will result in lower energy consumption, better handling and same braking performance at the expense of some ride quality.

Many people that refer to rock hard are those far exceeding the safe limits of the tire rating. I ran my EV tires at higher pressure than normal pressure but not unsafe. There are diminishing returns at both extremes of the scale for various reasons and road conditions.