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[Doug S]

Electric car manufacturers go to great lengths to encourage you to accelerate gently with eco driving meters etc. so I'm sure there is something in it.

There is some debate in the hypermiling community about whether it's better to accelerate hard to overcome the losses through the throttle bodies at small openings but the general consensus is to keep revs low at all times.

If the hypermilers are debating the point, you can be sure it's anything but a slamdunk either direction. If anybody's tested it, you can be sure these guys have!

...then accelerating using 660amps will use your power faster than 440 amps.

Of course it does, I said that in my original post. But you don't have to accelerate as long to reach your final speed! Seriously, if you're skeptical, as I was originally, test it yourself.

There is some loss with i^2 R losses.... But what I've seen in my battery testing as more of a factor... Is The more current you draw from a battery.... The less total energy you get out.

Yes, these are the extra losses that makes it not QUITE a wash, as I also said in my original post. But a modern EV is VERY efficient, even at its highest performance levels, and those extra losses just aren't very big.

I'd love to see real data on this. My testing has been very informal and limited to real-world commuting on different days, so it's hardly conclusive. It's enough to convince me that the difference is small, but not HOW small.

[protomech]

Example motor efficiency plot for an unspecified Parker GVM traction motor, similar to the one used in the Brammo Empulse



The vast majority of this plot shows very good efficiency, 93-96%. There are two regions where efficiency falls off:

1. Very low RPM, high motor torque. At very low RPM - such as accelerating from a stop - accelerating slowly is more efficient (say 40% peak motor torque = averages about 90% efficiency up to 1000 RPM) than accelerating wide-open (100% motor torque = averages maybe 75% efficiency up to 1000 RPM).

If you have a selectable transmission you want use a lower gear if available to avoid the low-RPM efficiency hole. Example: 750 RPM 300 motor Nm is 87% efficient (say 3rd gear), but 1500 RPM 150 motor Nm (same wheel Nm) is 93-96% efficient (say 1st gear).

This is where an Eco-like mode can help by limiting peak motor torque from a stop.


2. Very low motor torque. At high RPM, motor efficiency is largely independent of requested torque. However, very light motor torque load (< 10% peak) starts to drop off in efficiency again.

Not much you can do about this if you have a direct drive system. Perhaps apply pulse & glide techniques if constant operation puts you in this smaller efficiency hole. However, if you have a selectable transmission then you can upshift to decrease motor RPM and increase motor torque for a given wheel torque target. ie, 30 Nm 7500 RPM is < 93% efficient, but 90 Nm 2500 RPM is 93-96% efficient.


It's also worth pointing out that efficiency in the second region is still quite good, and that typically the energy spent accelerating from a stop is quite small on a motorcycle relative to energy spent overcoming drag. Dropping 1 mph off your travel speed would likely more than make up for the extra energy lost in dozens of hard launches at a stoplight.

And motor efficiency WILL depend on the motor in question.

2004 Prius motor:


Remy HVH250 traction motor, as used on the Lightning bike:

[Doug S]

That's some GOOD stuff, protomech! There's a ton of red in that first graph, that's great to see. Is that motor similar to the one in my Zero SR? And exactly what type is it? I'm guessing it's a "permanent magnet AC" motor or a "brushless DC" motor. The Lightning uses a field coil motor of some sort, doesn't it? I believe that's why it has so much more horsepower than the Zero SR but not all that much more torque. Same logic for the Mission.

[benswing]

...then accelerating using 660amps will use your power faster than 440 amps.

Of course it does, I said that in my original post. But you don't have to accelerate as long to reach your final speed! Seriously, if you're skeptical, as I was originally, test it yourself.

I did test it myself over the course of two separate 5,000 mile road trips.  I'm not sure how much more evidence you require.  Accelerating harder eats some if your range despite getting your desired speed slightly faster. 

On the current setup if my 2012 Zero S the Sport mode makes the full 660 Amps available while Eco mode limits me to 440 Amps.  I've done this experiment dozens of times in the past month, plus many other times over past 2 years.

[benswing]

Also, I just re-read the previous posts you have been alluding to and I think I understand where our disagreement lies.  It seems as though you object to when I used the word "strongly" to identify how hard acceleration affects range.  While hard acceleration is not the strongest factor, I have found it to affect my range consistently.  So if that was your main dispute, then I partially agree with you.  Could have used a different adjective.

Also, this is a case in which you have done your experiments and I have done mine and we appear to have come out with contradictory results.  So on this point we shall have to agree to disagree.

Cheers!

[frodus]

That's some GOOD stuff, protomech! There's a ton of red in that first graph, that's great to see. Is that motor similar to the one in my Zero SR? And exactly what type is it? I'm guessing it's a "permanent magnet AC" motor or a "brushless DC" motor. The Lightning uses a field coil motor of some sort, doesn't it? I believe that's why it has so much more horsepower than the Zero SR but not all that much more torque. Same logic for the Mission.

Here's a new term: IPM, or internal permanent magnet. As opposed to having magnets on the outside of the rotor (surface permanent magnets or SPM), the magnets are embedded in the rotor to provide a better magnetic flux profile.

Mission uses either PMAC IPM or AC Induction in their custom motors. The IPM has a peak torque of 115Nm and a peak power of 85kW. The induction motor has 70Nm and 65kW respectively.

Lighning uses a Remy HVH250 motor, which is a PMAC IPM motor. The standard HVH250 has a peak torque of 325Nm and a peak power of 82kW. In the same HVH250 family, there are higher power models that hit 150kW and 440Nm.

Brammo uses a Parker GVM motor, which is a PMAC IPM motor. Brammo lists their specs as a peak torque of 90Nm and peak power of 40kW with the Empulse R. I know for a fact that the motor in mine has some overhead with the settings in the Sevcon, so the peak torque is going to be in the ~110Nm range.... which would boost the power as well. I think they use the GVM142-150, which lists a peak torque of 113Nm and a peak power of 65kW.

Zero S/SR uses a PMAC SPM motor. Zero lists the motor as having 144Nm of peak torque and 50kW of peak power.

All of those motors have a similar stator (wound coil stator, outside of the motor), but are a little different between the SPM and IPM. A lot of the racing motors (Yasa, Remy, parker, etc) are IPM motors.

[oobflyer]

Interesting discussion - we have some well-informed members of this forum!

I was a wanna-be engineer at one point in my life and so studied physics/calculus for several years (ended up in the medical field - go figure).

To get back to basics, if memory serves, Work = Force x Distance, and Power = Work/Time. So, with Time in the denominator, more Power would be required for the same amount of Work done in a shorter amount of time - correct?

This is my understanding anyway - when I'm making a longer run (on one of my electric bikes or in my electric car) I accelerate slowing - hoping to conserve some of the battery capacity.

[Doug S]

It seems as though you object to when I used the word "strongly" to identify how hard acceleration affects range.

I overstated my case as well. I said acceleration has "little to no" effect on battery usage, and that's not true. I should have said that I believe it has only a small effect.

I think we're on the same page.

[CliC]

Benswing, have you had any cooling issues while taking advantage of your newfound acceleration? I have a 2012 DS, and because there's no DSR, and because my nearest dealer is probably dropping Zero, I'm considering hanging on to mine for awhile and maybe doing this upgrade.

[benswing]

Doug S, I agree. 

CiiC, I haven't had any overheating problems during regular use including highway riding (about 10+ miles at 70-80mph).  The only two times it ever overheated were (1) going 100mph and (2) riding up Mt. Washington a little too fast.     (I made it up Mt. Washington the 2nd time without overheating going the normal speed.)

I've had a great experience using the size 6 controller and haven't had any issues relating to that part.  However, I now need to change my tires again from so many miles!

[WindRider]

Full throttle acceleration power wheelie romps on my FX make the energy bars go away with shocking rapidity. 

Gentle acceleration makes the bars last a lot longer. 

That is my humble observation.