Does acceleration affect range?

So obviously your speed greatly affects range. But i was thinking, does your acceleration make much of a difference?

Using high power to accelerate obviously draws more energy (per second), but the acceleration also ends faster. Then the opposite is true for low power acceleration. Assuming you had the same top speed in both scenarios, would the energy consumption be much different?

Edit: I'm talking about from a standstill on flat ground.

Simple answer, yes, acceleration is something that drains the batt. faster, much faster than a ride with much less acceleration. Absolutely.

On 20A, I get 40 miles... but on 100A, I get 15 miles..but the acceleration is stupid fun. Same top speed.

It's hills that really suck it out of your pack.

DogDipstick said:

Simple answer, yes, acceleration is something that drains the batt. faster, much faster than a ride with much less acceleration. Absolutely.

On 20A, I get 40 miles... but on 100A, I get 15 miles..but the acceleration is stupid fun. Same top speed.

Click to expand...

Would this be the case even on a completely flat ride? Because i know powering up hills will majorly drain the battery as the last poster said.

Username1 said:

DogDipstick said:

Simple answer, yes, acceleration is something that drains the batt. faster, much faster than a ride with much less acceleration. Absolutely.

On 20A, I get 40 miles... but on 100A, I get 15 miles..but the acceleration is stupid fun. Same top speed.

Click to expand...

Would this be the case even on a completely flat ride? Because i know powering up hills will majorly drain the battery as the last poster said.

Click to expand...

Yeah on the flat. Same differences. Up a hill, down a hill, whatever. Cuts my range in half or more.

It s called "WORK"... and WORK takes POWER and POWER takes ENERGY.

Work is defined as : "In physics, work is the product of force and displacement. A force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force. "

Now, to get the work done faster, you need more power (energy).

There is a set amount of work to go from point "A" to point "B" in ( the variable of ) time "T" ... and the speed of acceleration is the difference... in the work ( distance traveled in that "T") done between A-B in the time "T".. If "T" on 100A is 1/4 the time of "T" on 20A acceleration: there will have been 5x the consumption and same the "work" done.. even in that ( relative timeframe) period of accele ration... When not at max accel the work is still done, just spread over alot more time...

Example: ON MY BIKE:

Velocity change: 0-75Kmph
Time: 10sec, full throttle,
Weight: 118Kg bike/rider,
Acceleration: 2.08M/sec^2
Acceleration to gravity: 0.212 g
Distance: 104 meter
Force : 0.246 k(N)
Work: 25.6 k(N)meter
POWERR: 2.56Kw.. also known as 3.43 hp.


NOW: IF I can do that in ( 0-75Kmph) LESS TIME ( more acceleration I get: (Same WORK, MORE POWER DOWN AND MORE CONSUMPTION)

If I can do that in 8sec power is increased, and acceleration is greater in (Ft/Sec/Sec) and distance is lessened.. and if I can do that in 6 sec.. lookout.. I'm pumping a solid 5.72hp for a 0-75kmph run in only 62.5 meters distance.. alot more umph and alot more force (to accelerate the vehicle) , same work.... 25.6KNmeter on both pulls, but the 6 second run takes much more power.. and power uses energy...

5.72Hp is MUCH MORE energy than 3.43Hp... and the battery will show it.

The grade ( the vehicle is on) is negligible Imo.

So is the idea that you will always use the same amount of energy to accelerate to a certain speed (regardless of power level used), but if you do so quickly (high power) you will have traveled less distance, therefor reducing your total range compared to slower acceleration?

Username1 said:

So is the idea that you will always use the same amount of energy to accelerate to a certain speed (regardless of power level used), but if you do so quickly (high power) you will have traveled less distance, therefor reducing your total range compared to slower acceleration?

Click to expand...

Yep. Exactly.
Vehicles have a weight ( 118Kg) , and reach a speed ( 75KmpH): two (of the) constants of the eq.

....variables being how fast they get there ( how fast the acceleration works to get up to the speed, the time).. and how much power is used ( energy to complete the work) and this is dictated by the acceleration rate..

ON MY BIKE : First equation, taking ten seconds:
Velocity change: 0-75Kmph
Time: 10sec, full throttle,
Weight: 118Kg bike/rider,
Acceleration: 2.08M/sec^2
Acceleration to gravity: 0.212 g
Distance: 104 meter
Force : 0.246 k(N)
Work: 25.6 k(N)meter
POWERR: 2.56Kw.. also known as 3.43 hp.


If I can go from 0-75 in 6 seconds: ( I cannot, that would be a very very fast bike, 0-75 in 6 sec) ...

( accelerate much faster) ( takes loads more power, hence loads more energy, hence loads more battery capacity, same amount of work but much more energy and power used to get there ( to the 75Km/hr) in almost half the time ( and almost half the distance travelled to reach that 75Km/hr)

Change in Velocity: 75(Km/Hr)
Time used: 6 sec
Weight: 118Kg bike/rider,
Acceleration 3.47(M/Sec/Sec)
Acceleration against Gravity: 0.354G
Distance: 62.5 meters
Force: 0.41kN
WORK:25.6kNm
Power: 5.72 Horsepowa

https://www.engineeringtoolbox.com/car-acceleration-d_1309.html

Tradeoff being range: see how much more WORK is used when you have high vs low power: you can get twice (or more) the distance going along at low power not doing much work ( in acceleration). Acceleration takes power, just as any "load" takes power. When you accelerate fast you are using the load to speed up the vehicle, not just to move it along,overcoming ( the load of) gravity and rolling resistance and wind... But remember all those are still there to overcome whether you are fast or slow... and busting through it at 2X or 3x the acceleration is more load on top of the baseline of steady state consumption...

Best to give it some extra current to get to cruising speed quicker than to gingerly creep up to it over a much longer time in general within some limits. At starting RPMs you have very low efficiency in the motor, so dumping too much current,will result in a significant amount of it going into heating. Extra torque ( more than just maintaining speed) is required to accelerate, so some extra current will be required. Depending on load, motor (mass, dissipation, losses) and gearing, this extra current has various resultants in heating and duty cycle (time) before the losses become significant. At speed, assuming your running in the motors efficiency zone, you will run much lower current at steady state speed. If you limit accel current to just a few multiples of this steady state speed current, it should not be significant loss unless you spend much of your trips in stop and go traffic.

Also at speed, most setups use most of the motors output- battery energy fighting wind resistance, which is most of the ride time if your looking at range as the response. So most of the Battery range impact will be related to what top speed - wind resistance you run on flat ground. Hills are extra!

in many instances

wind speed and hills

far more penalty

than acceleration

Yes. What both these two guys note is that it is relative to the motor efficency and the forever load of drag ( rolling, gravity and air). The calculation I described above do not take that into account: pure acceleration of mass equations.. not including the coefficients or rolling resistance ( friction ) and air ( friction), or how many times I speed up or slow down during a certain ride ( variable) ( power is dissipated for every acceleration.. and also every deceleration, that mus be accounted for if we were to look at the problem empirically.. and these things add up) ....

Rolling and air become more exponentially the higher the speeds get. Ebike speed/power ratio is not encroaching high power 140-200mph Moto territory, where it begins to take a huge amount of power to overcome both air friction and rolling ect... ( hence fairing on rocketbikes and airplanes or they are never achieving the speed @ the power to fly or race)

Alot of it is to have the horsepower available for acceleration, vs not. I would always rather have Hp available for acceleration personally on any bike... Think of "Hp" as "how fast the WORK is done"... and if you have the available tq ( created through the winding) to accelerate (positive torque making acceleration) (Acceleration equals delta velocity divided by delta time.) (deltaV/deltaT) ( acceleration is not deltaV... DeltaV implies constant acceleration)...( delta-V is simply a change in velocity)( we look at acceleration here, not only the change in velocity, so we bring in Time), yes we all like that. The torque profile of a hub motor vs speed vs efficiency well defined and enumerated.

Well, no longer a simple question, Eh?

.. so on ebike the drag is not to great ( until over 30-50mph).. and a good "blip" on the throttle to get fast acceleration to the speed desired WILL save some energy consumption VS if you were to slowly creep up to speed ( and inherently spend more time in the lower less efficient range of motor speed and consumption) ...

Yes I would say you could "blip throttle " up to speed where the motor is happy and ride there more efficiently, than if you were to spend ( more) time in the driving tq regions of the motor rpm.

This is the beauty of a well setup and chosen efficiency range for the power levels used, and the scourge of any bad motor manufacturer... Try to get every bit of work out of the energy input... effectively... and hubs and mids are designed around this.

Both those guys are correct. ^^^ I was negating all rolling resistance and air drag in my eq example for sure.

Personally, I am a power junky, and IF I can accelerate like a demon I will, and doing this repeatedly uses more energy ( and goes faster more, gets to higher top speeds earlier, and result spend more time in the high consumption area of my ride, even thought my motor is 8-10% more efficient at 40mph vs 35mph.. ( I end up going farther ( distance) faster ( less time) and using more energy storage... braking more ( wasted umph, er, I mean energy) and accelerating more ( more umph!!!, more grinning and winning!!!! ) more often (inherently) .. and it is 60-70% more efficient at 90% of top speed than at 10% of top speed... (very inefficient when going low speed on my hub) ..

Always remember, when it comes to electric motors... it takes lots of power to spin it up, but less power to keep it spinning...

The distance is less at the faster rate, then the work is the same, ( same top speed same work but longer/shorter distance) but consider time, and throttle applications ( power to speed) and speed load ( wind rolling) ... and very well will take more. ( same distance same accelerations = different amount of work done)

The acceleration ( decrease in range) is really negligible.. unless you start stop alot and do it fast ( city driving mpg)... Unless you are drag racing ! At 20 A .. yes I go slow(er) top speed and get 40 miles.. but at 50A I go pretty fast accelerations and power to get to top speed and get 22miles.. much closer to the 15-16 miles I get at the absolute max of 100A.... mostly at top speed... ( I waste alot of heat here too, ).. not much differences in range, but still some cause of the increased ( difference of) distance and increased ( decreased) work done.

The psychological factor is important.

That fun feeling is 99.9% impossible to resist

so without a hardware limiter like CAv3

if your vehicle **can** use more power

you **will** get less range.

Self-control is a rare attribute among humans.

.. so on ebike the drag is not to great ( until over 30-50mph).. and a good "blip" on the throttle to get fast acceleration to the speed desired WILL save some energy consumption VS if you were to slowly creep up to speed ( and inherently spend more time in the lower less efficient range of motor speed and consumption) ...

Click to expand...

The efficiency curve of the motor is important, but few if any electric vehicle motors are more efficient - or even AS efficient - when accelerating as they are when cruising. When the load is high you get more heat production, and whenever a motor is producing substantial heat, energy is being wasted. I disagree about 'creeping' up to speed, as this is part of the proven method used to extend range when you are low on it or need to get more of it. I believe that batteries also have less capacity when drained quickly than slowly, negating any theoretical advantage of accelerating hard. This is one of those thought experiments that plays out one way in one's head, and another, different way in the real world.

Yes high discharge rates means less storage capacity.

Also voltage sag comes into play much earlier, so even the lesser amount of remaining energy is in effect inaccessible until the rate is reduced and voltage allowed to recover.

This one is hard to put a rule of thumb on. There are setups that are so inefficient for the first 10 feet of an acceleration, that changing the motor type can result in a 20% improvement in range, but only if you stop every block for miles. In that worst case situation, which is a very low powered, but high speed winding DD hub motor, the fix is simply to pedal for four strokes, then put on the throttle to finish your start.

But in general, acceleration is only noticeably inefficient, when you accelerate to a speed that hogs your watthours.

Best case for efficient acceleration would be a mid drive, and lots of shifting. But hardly worth the effort, just start up in a mid range gear is fine. But a very low power mid drive should not be started up in the highest gear. That puts you back similar to the low power dd situation.

This one is hard to put a rule of thumb on.

Click to expand...

Agree, it depends on a bunch of factors and your motor efficiency plot. Wishful that most of the common low cost motors are like a prius motor, but if we use the common plot, we can understand it a bit more IMO.

Let say that a moderate target cruising speed required 25 NM to maintain it. Even twice or three times that, would have little efficiency hit. If your target speed -current to make 60 NM, double is doable, but tripple is certain to waste a bunch more capacity into heating losses. Without testing it out on your specific setup, hard to make such a rule. Also note, the efficiency hit at torque levels below 20 NM at low rpms. Just wasting energy holding it back too much.