LOL Nope. Look at the voltage drop under load. Multiply voltage drop by current. It's a huge number. It's a lot of amps, and a lot of volts.
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
P3D+ 250 mile range with non-aggressive driving
- Thread starter khraiv
- Start date
Daniel in SD
(supervised)
Yep. The average efficiency might be 95% but it's way less at full load.
Not sure what kind of hills you guys are going up though that require any significant percentage of full throttle to maintain speed.
I think maintaining 60mph in a 4000lb car up a 7% grade takes 33kW of power (just for the vertical component, neglecting aero, rolling resistance, drivetrain losses, etc. those only add about 10-15kW more).
Wolfram|Alpha: Making the world’s knowledge computable
In summary, the headline for the OP should read: "Owner selects least efficient vehicle model, puts least efficient wheels on it, drives fairly quickly, and then complains about range being 20% lower than nominal"
I mean, golly gee willickers.... What's next? "I added a parachute on a cable and a boat anchor to drag behind my car, but now it's hurting my range!"
We live with the consequences of the decisions we make. It's not exactly like people haven't been informed that the larger wheels are less efficient than the aeros ("aero" is right there in the name!), particularly the 20s, and that AWD/P is well less efficient than RWD.
ℬête Noire
Active Member
This isn't true (depending on the specifics of the difference between the two rates of acceleration, the hardware, etc.). The reason is that although the vehicle traveling at 65mph has lower kinetic energy than the one traveling at 66mph (( (1 - 65^2/66^) * 100% = 3% less )), thus requires 3% less energy (power) in acceleration to get there, to generate force the motor, power circuits, and battery operated at substantially lower efficiency during the faster acceleration. This is because electrical power losses from resistance are proportional to the square of the current. So if for example you double the current to the motor current it doubles the torque but quadruples the losses. For the heaviest acceleration that the Model 3 is capable the current it's using is several fold above a modest acceleration.
Also, if you're attempting a very fast acceleration you can start to have meaningful increase in traction loses, another source of efficiency loss.
EDIT: Once you get to the point that air resistance is significant, there is something of a sweet spot where slightly faster acceleration uses less total energy to reach a given velocity. This is because your net acceleration is the difference between the wind drag and the force your drive train is applying to acceleration the car's mass. You can see this without even using numbers by imagining that you are slowly reducing how much force the motor is apply towards the point that it just counters the wind drag and thus never reaching the velocity which in turn means that the total amount energy used is approaching infinity.
This is actually also the case with the rolling friction, as well, but these vehicles have such low rolling resistance that you pass that sweet spot at a very low acceleration rate, I expect to the point that it's swamped by the computer/control system electrical use overhead.
Last edited:
SageBrush
REJECT Fascism
Maybe.
You are probably right if the other driver is flooring the go pedal, but I'm not so sure about a case of slow Vs moderate acceleration. The reason is that motors also have an efficiency curve that peaks somewhere in the 30 - 50% range of maximum power.
HOWEVER, whatever the differences are they are not the main determinant of energy economy. Un-needed braking and regen tell the tale. And it is typical that drivers that get off the line aggressively coast less and regen/brake more. So there is an association but the cause is not what most people presume.
Daniel in SD
(supervised)
But what is the battery efficiency versus load? I agree that 100% acceleration is probably very innefficient but 50% acceleration is still very fast and has one quarter the loss. And the motor/inverter is often more efficient at higher loads.
Ok. I feel like most of agree on all the different factors. Who’s going to create a MATLAB model so we can find the optimum way to get over a hill?
I think rolling resistance is proportional to speed so the loss is constant with distance.
Ok. I feel like most of agree on all the different factors. Who’s going to create a MATLAB model so we can find the optimum way to get over a hill?
I think rolling resistance is proportional to speed so the loss is constant with distance.
But what is the battery efficiency versus load? I agree that 100% acceleration is probably very innefficient but 50% acceleration is still very fast and has one quarter the loss. And the motor/inverter is often more efficient at higher loads.
Ok. I feel like most of agree on all the different factors. Who’s going to create a MATLAB model so we can find the optimum way to get over a hill?
I think rolling resistance is proportional to speed so the loss is constant with distance.
Eh forget the model. Just put the car on Mustang dyno with RPM hold feature, and map out real efficiency on a 2 dimension map indexed by speed and throttle position. You'll need to have the dyno rented all day, at least.
...and then remember the map when driving.
ℬête Noire
Active Member
There's multiple fold below 50%, though, that are many people will find entirely acceptable.
Does the normal Model 3 UI have an instantaneous kW readout like the Bolt does, where you can see this? Or do you have to put the vehicle into that factory test mode?Which gets to why it matters when the question is "energy required to reach velocity X". The longer the distance it takes to reach velocity X the more drag energy adds up. It isn't factor in acceleration a discussion if you're then parleying that into an overall discussion of the energy required to travel distance X. You can ignore it there since it's ultimately a fixed cost.
Last edited:
ℬête Noire
Active Member
This has not been my experience. Regularly "standing on it" has a very notable impact the Bolt's range (it's UI has fairly good immediate and mid-term feedback) and that is very much an independent decision from choices on when and how to de-accelarate.
Also, regen is so efficient roundtrip (wheels to battery to wheels) that losses from it tends to get swamped, as it stop & go usually means you're spending a lot of time at lower speeds (thus lower air drag) anyway.
The biggest impacts are actually speed you travel at (tends to be far more pronounced in the Bolt since the "knee" in it's curve is about 10mph slower than with the Model 3, as it has a much higher Cd) and whether or not you have/need HVAC.
SageBrush
REJECT Fascism
SageBrush
REJECT Fascism
Friction from rolling resistance is not speed related for our context.
Rolling forces (Newtons) = mass * g * f
Energy (joules) = mass * g * f * distance.
The extra feet traveled to reach the desired speed at a lower acceleration is trivial since f is ~ 9/1000 kg
Ignoring drivetrain ( battery, inverter, motor, and gears) losses, energy spent to go from naught to X is imbued kinetic energy
= 0.5 * mass * v * v
The drivetrain losses do not change much unless we are talking about corner cases (really slow or really fast) and the KE is the same.
ℬête Noire
Active Member
It was for the post I was addressing, although as an aside for completeness about how the efficiency curves interact.
ℬête Noire
Active Member
Then it's "standing on it" neck and neck with "using friction brakes".
Regen is really quite efficient. Although not as good as just letting it roll to a stop, rolling to a stop tends to be more difficult in traffic in a dense urban area.
Of course if you're standing on it a lot in semi busy streets you're more able to get up to speeds where air drag matters, too. Also, if you are getting up there to higher speeds you're under more pressure to use friction breaks because the distance required to slow extends out.
Thus, again, ultimately the speed matters. Although even if you don't use the faster acceleration to attain higher speeds the faster acceleration is going to hammer your range.
Last edited:
VLTWGGN
Member
I'm not sure what you're getting at, but as an EV driver for 4 years already, I'm not complaining...just reporting a data point? I used to be a battery engineer for Ford...I know my EVs
roblab
Active Member
So, nearly every post is about accelerating up to speed as being the reason the 3 isn't coming in with advertised numbers, when according to physics, and my understanding of driving my 3, it's how fast you drive. The guy was doing 80. If I want to get advertised range, I go 65. I also leave the aero wheel covers on. I have taken the 3 on a little 300 mile round trip, about half freeway at 70+ and half mountain roads at 55+. I got a calculated 318 miles range. Oh, and I love punching it at lights. But in my experience, you get about 3/4 of acceleration loss back through regen, and we're talking of seconds of driving, rather than hours at speed.
In other words, SPEED is what affects the range, not acceleration. Gas cars, not having regen, are more affected by acceleration losses, but they, too, lose range (miles per gallon) when driving fast. If you want to make a trip with only one charge stop instead of two, you gotta slow down nearly every time.
In other words, SPEED is what affects the range, not acceleration. Gas cars, not having regen, are more affected by acceleration losses, but they, too, lose range (miles per gallon) when driving fast. If you want to make a trip with only one charge stop instead of two, you gotta slow down nearly every time.
ℬête Noire
Active Member
According to your incomplete understanding of physics, you mean.
It's both that matter, along with using friction braking. Faster acceleration costs significantly more as it is less efficient electrically, even though it is the same on the Newtonian mechanics side.
VLTWGGN
Member
According to your incomplete understanding of physics, you mean.
Exactly.
It's all a function of battery discharge rate. That means accelerating fast (current draw), AND driving fast (drag), AND wheels (current draw for torque).
SageBrush
REJECT Fascism
SageBrush
REJECT Fascism
ℬête Noire
Active Member
If the chemical to electrical to mechanical power conversion functioned at ideal it'd be fine. You'd draw double the current for 1/2 the time and it'd cancel out. But it doesn't actually work at that ideal.
Similar threads
- Question
