P3D+ 250 mile range with non-aggressive driving

[ℬête Noire]

Not even close.

Around 60% overall.

It's even higher than that wheel-battery-pavement....and even that wouldn't support you assertion. Setting aside what's the alternative, again?

 

[ℬête Noire]

Exactly

AKA "Yeah, you were right Bete".

 

[Jedi2155]

Not even close to 100 kw. The battery is about 95% efficient so at even 400kw that would only be about 20 kw.

A typical lithium-ion battery has a one-way Faradiac effiiency of 98-99% which equates to about 97-98%. The majority of losses are in the PCS rather than the cells themselves depending on discharge rates. At 0.1C < 0.5C (8 to 40 kW) discharge rates thats being discussed here (going up a hill), the heat losses are not worth mentioning.

Same energy different power. Yes I agree. I think people trying that "hyper-mile" by feel are at most just inadvertently going slower, losing aero losses on the way up and then starting slow at the top again. Might as well just go slower 100% of the time, perhaps saving even more energy.

edit - but you didn't put a unit for drag. Energy or power, it matters. Power is cubed.

So far this thread has split into two components, going uphill and downhill. The 2nd part was discussed first which comprises ofJ: Is the increased aerodynamic drag from coasting worse than the efficiency losses incurred by utilizing regen while going down the hill? Which imo hypermiling experience of the opinion that aerodynamic drag is the lesser of the 2 evils (when traffic is also considered), but I haven't put the actual numbers. So someone wants to do the matlab/spreadsheet model? lol

Its been 6 years since I last calculated used this equation but I'll lay it out for you guys:

Ptr = Tractive Power
V = velocity
m = mass
g = gravity
B = grade angle
C0 = rolling resistance
C1 = (forgot what this is lol, but it has a unit of s^2 / m^2)
p = density of air
Af = frontal area of the vehicle)
Cd = coefficient of drag (air)

Power required at constant velocity:
Ptr = V*[ m*g*sin(B) +(m*g*C1 + 0.5*p*Af*Cd)*V^2 + m*g*C0]

Someone with more interest than me, can use it for your pleasure.

Regarding regen efficiency, someone actually mapped out the efficiency for the Volt motor which was around 0.6 to 0.9 efficiency with the max efficiency at the highest deceleration rates and it quickly dropping off. My personal technique (as a feeling) was to maximize velocity while minimizing regen going downhill, then at the bottom of the hill kick on the full regen so I get the maximum regen at its highest efficiency point. All this barring traffic. That way I minimize conversion losses until the very end.

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.

Sure if you spend more time speeding up to X speed, then your sum rolling resistance drag will be greater than if you accelerate quickly to X speed. However the sum of your rolling resistance will be greater over a given distance than if you slowly accelerated to X speed because you spend a greater amount of time at X speed with the increase resistance. Keep in mind that force imparted by rolling resistance is linear to velocity (as seen by my above equation).

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

Battery engineers unite! Been an EV driver for 10 years and a battery engineer for several years lol. Will you be going to the Battery Show in Novi next month?

Still my favorite business card I've collected over the years....

 

[JG T3SLA]

Has Tesla ever confirmed kWh size of P3D? Best I can find is people assuming 75 but speculating it could be 80. Anything definitive released that I missed?

 

[Maximilien]

Has Tesla ever confirmed kWh size of P3D? Best I can find is people assuming 75 but speculating it could be 80. Anything definitive released that I missed?

I think one of the EPA report shows 78.2 kWh usable battery and 80.5 kWh for all LR.
Ironically, it is more than S85 which was known to be 77.X kWh.

 

[ord3r]

No tests necessary, the laws of physics say the faster you accelerate the more power you need to do so.

You're forgetting the other variable in the equation: time. The time needed to get to a speed is reduced with faster acceleration. In a perfectly efficient system, if you had a goal of getting to lets say 65MPH, it would not matter how fast you accelerate, it would use the same energy to get there. Of course accelerating faster will use energy faster, but it also will reach speed faster at a rate proportional to energy usage.

The reason Tesla's use more energy when accelerating faster is they are not perfectly efficient systems. Per 'Captain Zap': "Resistive power losses in the battery pack, drive inverter, motor, and associated wiring are proportional to the square of the current. So doubling the motor current doubles the torque but quadruples the losses."

Why does accelerating fast use more energy than accelerating slowly?

 

[khraiv]

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.

Being I'm the original poster, I'm guessing I'm "the guy". My average speed was no where close to 80. I said limit+5. That's 30 in a 25, 40 in a 35, etc. Sure, there were times I hit 80, but overall this was a *very* average drive. In any case, this topic wasn't even about the reduced range, it was about the *estimates* using the incorrect range... But I guess everyone wants to read the title and reply.

 

[ℬête Noire]

Sure if you spend more time speeding up to X speed, then your sum rolling resistance drag will be greater than if you accelerate quickly to X speed. However the sum of your rolling resistance will be greater over a given distance than if you slowly accelerated to X speed because you spend a greater amount of time at X speed with the increase resistance. Keep in mind that force imparted by rolling resistance is linear to velocity (as seen by my above equation).

That's why I said that component is a wash when you're talking about energy used countering it over total distance traveled, rather than energy used to counter it while getting up to a given velocity. If I travel at x velocity with y rolling resistance then I'll have 2y rolling resistance at 2x (there can be small variations here depending on specifics of drivetrain design but especially when you have no variable gearing, as with Teslas, linear is a safe assumption for this level of precision). The cumulative energy from the rolling resistance is that y or 2y multipled by travel time. Since t = d/v leads to a velocity of 2x having 1/2 the t of velocity x, when you multiple y * t and 2y * t/2 you find they have the same total energy, yt.

This means for a given vehicle, the total cumulative rolling distance is directly related to the distance traveled. If you double the distance, you double the cumulative rolling resistance. It's independent of the speed at which you traverse the distance (and thus the variations in that speed, AKA acceleration, as well).

So when you're looking at the total drag from rolling resistance incurred to reach a given velocity, since the slower acceleration actually increases the distance you travel over to get to that higher speed (as well as the time to do so), the slower acceleration leads to a higher cumulative incurred rolling resistance.

 

[ℬête Noire]

Being I'm the original poster, I'm guessing I'm "the guy". My average speed was no where close to 80. I said limit+5. That's 30 in a 25, 40 in a 35, etc. Sure, there were times I hit 80, but overall this was a *very* average drive. In any case, this topic wasn't even about the reduced range, it was about the *estimates* using the incorrect range... But I guess everyone wants to read the title and reply.

So what was the mix of road traveled?

More importantly, I notice you're in Phoenix. And it's summer. How cool do you like you vehicle, are the windows tinted? Also where was the car parked, relative to the sun and such, and were you making a lot of short trips?

We've seen reports of what appears to be battery temp management eating up a lot of kWh, and of course cabin cooling has it's costs (it's actually the same heatpump used for both of those). It's not easy living on Tatooine, after all.