theaveng
Well-known member
When does the motor reach 3000rpm?
At what RPM is the motor most efficient?
garygid
Well-known member
A typical tire, at some typical pressure, with a typical load in the car,
is approximately 6 feet per revolution, or about 850 rev/mile.
The "transmission" is approximately an 8 to 1 reduction in rpm,
so the motor must turn about 6800 revolutions to go one mile.
Thus, at 6800 rpm one is going 1 mile per minute, or 60 mph, approximately. 
So, 3000 rpm would be about 26 mph.
As a rough approximation, add 2 zeroes to the mph to get rpm:
93 mph is about 9300 rpm.
A somewhat closer approximation is to add 10% to that rpm:
9300 + 930 = 10230 rpm (roughly)
For those that enjoy extra precision, but are not concerned about
accuracy, you could say that this rpm = 10230.534296
theaveng
Well-known member
garygid said:
Thus, at 6800 rpm one is going 1 mile per minute, or 60 mph, approximately.
So, 3000 rpm would be about 26 mph.
I thought I read elsewhere that the motor was limited to only 6000 rpm? That means it could never reach 60mph (by your calculation). Maybe I misunderstood about the rev limit.
derkraut
Well-known member
theaveng said:
garygid said:
Thus, at 6800 rpm one is going 1 mile per minute, or 60 mph, approximately.
So, 3000 rpm would be about 26 mph.I thought I read elsewhere that the motor was limited to only 6000 rpm? That means it could never reach 60mph (by your calculation). Maybe I misunderstood about the rev limit.
You misunderstood. garygid's calculations are correct.
garygid
Well-known member
I think that the motor rpm limit is somewhere between
10,000 and 11,000 rpm.
theaveng
Well-known member
So the motor spins 10,600 rpm at the max speed of 94? Wow. I hope it's well built.
So when I rent my Leaf, 26 mph will put me at the motor's torque peak. Good to know. I was impressed with how fast the thing accelerated during my testdrive. (Contrary to some poster's bosses' opinion, the acceleration is good.)
rslatkin
Well-known member
theaveng said:
So the motor spins 10,600 rpm at the max speed of 94? Wow. I hope it's well built.
So when I rent my Leaf, 26 mph will put me at the motor's torque peak. Good to know. I was impressed with how fast the thing accelerated during my testdrive. (Contrary to some poster's bosses' opinion, the acceleration is good.)
An electric motor has its max torque at zero speed, not 3,000rpm. That's part of why it feels so zippy.
theaveng
Well-known member
Now I'm really confused. In another topic a person stated the max torque was at 3000rpm. He wanted to add a 2nd gear in order to "adjust" the motor speed from 7000 to 3000 at highway speeds.
sproqitman
Well-known member
theaveng said:
Now I'm really confused. In another topic a person stated the max torque was at 3000rpm. He wanted to add a 2nd gear in order to "adjust" the motor speed from 7000 to 3000 at highway speeds.
It's a synchronous AC motor. The power control unit adjusts the relative angle between the "active" winding and the magnet to achieve maximum torque at ~3000 RPM. The torque curve is then essentially flat from 3000 to max RPM (10,200). You could change the programming in the control unit to have maximum torque at 0 RPM, but my understanding is that Nissan wanted the Leaf to feel more like a "normal" car.
Don't ask me to follow up. That's the limit of my knowledge of AC motors ;-)
leafedbehind
Well-known member
The Fit EV doesn't limit low-RPM torque nearly as much -- it is easy to chirp the tires off the line. But then you don't feel the surge of extra power when you hit 20-25 mph like you do in the Leaf .
EVDRIVER
Well-known member
- Joined
- Apr 24, 2010
- Messages
- 6,753
The LEAF torque at low speed is software limited by a KW reduction.
theaveng
Well-known member
sproqitman said:
The power control unit adjusts the relative angle between the "active" winding and the magnet to achieve maximum torque at ~3000 RPM. The torque curve is then essentially flat from 3000 to max RPM (10,200).
Oh I had read the torque curve drops off. This is why I want to buy a Leaf (or Volt), because as an electrical engineer the technology fascinates me. Unfortuantely I cannot afford the $30,000 pricetag; I'll buy used for ~15,000.
dcpatters
Active member
The LEAF does indeed limit torque at low speed, full throttle input?
theaveng
Well-known member
I spun the Leaf's tires during my testdrive. Ooops. Anybody (like a certain person's boss) who says the car cannot accelerate does not know what they speak of.
sproqitman said:
It's a synchronous AC motor. The power control unit adjusts the relative angle between the "active" winding and the magnet to achieve maximum torque at ~3000 RPM. The torque curve is then essentially flat from 3000 to max RPM (10,200). You could change the programming in the control unit to have maximum torque at 0 RPM, but my understanding is that Nissan wanted the Leaf to feel more like a "normal" car.
Don't ask me to follow up. That's the limit of my knowledge of AC motors ;-)
You have it backwards. Most EVs have flat torque from 0 RPM to somewhere around 3000-4000 RPM (peak torque is limited by peak current across the motor windings). Above 3000-4000 RPM torque falls off but power remains at it's peak (typically limited by battery current) until you approach top speed when motor efficiency really starts dropping off.
TonyWilliams
Well-known member
drees said:
Above 3000-4000 RPM torque falls off but power remains at it's peak (typically limited by battery current) until you approach top speed when motor efficiency really starts dropping off.
Using the classic horsepower formula:
(RPM * Torque FootPounds) / 5252
hopefully will explain to folks why the horsepower can remain the same above max torque RPM at 3000 RPM.
If the maximum torque is 200 ftlbs multiplied by 3000 RPM = 600,000, divided by 5252 is 114 horsepower.
600,000 divided by 180 ftlbs = 3333 RPM to make the same 114 horsepower.
600,000 divided by 100 ftlbs = 6000 RPM to make the same 114 horsepower.
600,000 divided by 10,300 RPM = 58 ftlbs to make the same 114 horsepower at 94 mph (max speed).
I don't have any idea how much torque is actually produced by a LEAF at these various RPMs, but I hope the exercise helps.
BraveLittleToaster
Active member
theaveng said:
So the motor spins 10,600 rpm at the max speed of 94? Wow. I hope it's well built.
So when I rent my Leaf, 26 mph will put me at the motor's torque peak. Good to know. I was impressed with how fast the thing accelerated during my testdrive. (Contrary to some poster's bosses' opinion, the acceleration is good.)
Ah, someone's just come over from the ICE camp without knowing that electrics and ICEs are different.
Yeah, electric motors routinely spin to well over 10,000 RPM. A Dremel for example, can get around 13,000 RPM. It's because they're far easier to balance than an ICE is, and just as importantly, they're astoundingly simple. There's only one moving part.
Your typical automotive engine maxes out around 6,000 RPM because its pistons turn a crank shaft that is inherently *un*balanced. It's a very delicate engineering and machining task to even get it that far. That unbalancedness will shake the engine apart at high RPM if you let it.
Electric motors have been far superior to internal combustion engines in many respects for a very long time. The *only* problem is carrying the fuel around with you.
sproqitman
Well-known member
drees said:
sproqitman said:
It's a synchronous AC motor. The power control unit adjusts the relative angle between the "active" winding and the magnet to achieve maximum torque at ~3000 RPM. The torque curve is then essentially flat from 3000 to max RPM (10,200). You could change the programming in the control unit to have maximum torque at 0 RPM, but my understanding is that Nissan wanted the Leaf to feel more like a "normal" car.
Don't ask me to follow up. That's the limit of my knowledge of AC motors ;-)
You have it backwards. Most EVs have flat torque from 0 RPM to somewhere around 3000-4000 RPM (peak torque is limited by peak current across the motor windings). Above 3000-4000 RPM torque falls off but power remains at it's peak (typically limited by battery current) until you approach top speed when motor efficiency really starts dropping off.
Yes, I do have it backwards. I was mis-remembering this thread http://www.mynissanleaf.com/viewtopic.php?f=27&t=5323, and swapped torque for power.
theaveng
Well-known member
BraveLittleToaster said:
Yeah, electric motors routinely spin to well over 10,000 RPM. A Dremel for example, can get around 13,000 RPM. It's because they're far easier to balance than an ICE is, and just as importantly, they're astoundingly simple. There's only one moving part.
Yeah I know motors are simpler, cheaper, etc but you still have to hold the thing together at high speeds. Ever heard of the CDs that disintegrate because they were spun too fast?
