Acceleration in an EV: Is it wasteful, as in an ICE?

It's definitely not the most efficient way to drive but spirited driving and regen can warm the battery up giving better efficiency later in your trip so its not all bad

 

I believe conventional wisdom is that slow acceleration is best for maximizing range in EVs.

The range game for EVs is about managing the (more) finite storage of energy over a distance. Since you get maximum torque from ~0RPM, you don't need to apply full power to get moving. Yes, more power will get you moving faster, but at the cost of many more electrons over a much shorter distance. This is why Green mode really dulls the accelerator response.

An analogy: You can chug a can of your favorite beverage in 2 minutes or you can nurse if for 2 hours--either way, you drink the same amount, but the experience you get is very different. The E-Power gauge basically shows you how quickly you're using your energy supply for acceleration, from "sip" to "chug".

 

Send it. We didn't decide on the mini se as the champion of efficiency or range... we wanted to drive!

 

Let's remove the complexities of efficiency of the motor controller(s) and drivetrain, etc... and go to the old measure of horsepower... work done over time... so, it stands to reason, that if you are doing the same work, but over less time, you are using more resources... so on that basis, I would say, yes, it uses more watts.

 

Aye... sadly, automotive manuals (POH) feel lacking to me in regards to performance data and power curves

 

Andy Miles attempted to address this very question in 2018. He thinks the rapid acceleration causes losses in the system (air resistance, rolling resistance, frictional losses in the drive train).

https://cleantechnica.com/2018/04/16/how-ev-range-is-affected-by-quick-acceleration/

 

Well, watts too, are a statement of work done over time... I probably should have used that term instead of horsepower... so then the question is distilled, does watts spent physically equate to watts consumed electrically? Which brings the question of efficiencies of drivetrain back in...

that being said, whilst WOT vs gentle would use more watts electrically to satisfy the demand of watts physically, you are still leagues more efficient than an ICE would be doing the same activities.

 

From what I can gather, there are two things here, but neither would seem to be huge.
1) In your scenario above, your average speed over the mile is close to 60MPH in the fast case and as low as 30MPH in the slow case. Higher speed for a longer period of time = more losses to aero drag.
2) Batteries have "internal resistance", which causes energy lose (which essentially leads to warming the battery). Power loss through a resistor is proportional to current squared, whereas the power output of the battery is proportional to the current. In other words, double the power out of the battery, and you quadruple the energy losses within. Now that's only for half the time, but you are now back down to double the total energy lost due to internal resistance.

I can't think of other factors off hand, but I'm sure there are some.

I think the issue is more likely to be cumulative. Someone who is driving spiritedly is not going to just goose it to 60MPH and then hold a flat speed for the rest of the drive. More likely, they are going to accelerate more quickly more often and those incremental losses add up.

 

I keep thinking the abbreviation "WOT" doesn't sound right for an electric car. However, in its favor, it doesn't have the controversial political connotations of abbreviating "All-Out Current."

 

My underdeveloped knowledge of physics leads me to concur that the motor efficiency should be pretty consistent, going "faster" is just spinning things more. So yeah, the various resistances and friction are going to be greater. On the other hand, don't wind turbines "make" more electricity by spinning faster, and isn't an EV motor the opposite so it would cost more electricity to go faster?

What we have seen is running the SE on the track for a period of time causes the batteries to heat up to a point of losing efficiency, but I doubt a quick acceleration from an intersection is going to heat them up that much.

What we really need is some performance tests of an EV in a vacuum...

 

Can't wind-resistance be ignored when comparing the energy used to accelerate ICE- and battery-powered vehicles?

 

A real-world consideration would seem to be that if you're always giving it full-current, you're also probably going to need to use friction-braking more often.