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Highland top speed reduced…
- Thread starter miatadan
- Start date
Y I could see them waiting until Juniper. But nerfing the S but not the X doesn't make sense to me now matter how I slice it in my head
Your assumption doesn't consider the type of battery (discharge characteristics), interference, or controller programming.
If programming was irrelevant, stall speed is ALWAYS the highest amount of draw on an electric motor, meaning 1 rpm has the largest draw, not 3000 or 4000, whatever 50 mph is.
Just because you see less power at higher RPM, does not mean it's drawing less power. It means other variables are to be considered. This is why we see 7% +/- battery loss on a 1/2 mile run in 15.2 seconds @ 175 mph, but only 2% battery loss in a 1/4 mile run in 9.3 seconds @ 150mph in a plaid.
No, physics does not work that way. You are discussing torque (current) without RPM (voltage). However, this is not WORK. Work requires force AND distance. Torque by itself is not work.
Horsepower = Power = Watts = Torque * RPM = Amps * Volts
A motor at 0 RPM takes no power because it does no work. There is basically no draw on the battery, despite there being a ton of torque. The inverter converts 400V and 1A at the battery to 400A and 1V at the motor (400W). The battery sees only that 400W load, and all of this turns into heat in the motor. However, the instant the rotor starts spinning that voltage goes up, and thus the work being done goes up.
Yes it does. We're literally talking about the draw from the battery. You can graph the draw from your battery, and you can see that it does not go up as you go faster. In fact, it drops as you go faster. This happens because as the RPM goes up, the torque goes down, and the torque goes down faster than the RPM goes up due to the back EMF of the motor.
If the motor output went down but the battery draw went up, all of that would need to go into heat somewhere. Tell me, where is that heat, and why does the electric motor drop from 98% efficency at 8000 RPM to 20% efficency at 16000 RPM?
Here's the chart of battery power vs speed in a Model 3. Explain how the battery is doing more work at higher speeds.
Let's do some math.
Plaid battery capacity = 97 kWh
1000 hp = 746,000 watts
746,000 watts for 9.3 seconds = 1,930 watt hours
746,000 watts for 15.2 seconds = 3,150 watt hours
1.93 kWh / 97 kWh = 2.0% - Dead on.
3.15 / 97kWh = 3.2%. - Nowhere near 7%.
But you're saying that we only use 2.0% like expected in the first 9.3 seconds. So to get to 7% in the next 5.9 seconds, we need to use up 5% of the battery in those 5.9 seconds. 5% is 4.85kWh. To do that in 5.9 seconds takes 3,000,000 watts. This would be 4,020 mechanical HP. But you're saying it's not, it's just ineffeiceny going to heat, and for the last 5.9 seconds, the motor is suddenly only 20% efficent despite being about 98% efficent 0-150 MPH. All without the motor turning into a molten slag heap.
Even if you do 7% over 15 seconds, that's 1,630,000 watts, which is 2,185 HP, or less than 50% efficency for the motor.
Sorry, but that's not happening, and your numbers are way off, and your understanding of how the electrical power output of a battery relates to the mechanical work done by the motor in an EV is off.
The fact that you aren't familiar with, or don't understand stall current, means there's no reason to carry on the discussion because that's a very basic concept of electric motors.
No amount of stitching together conjecture is going to overrule facts.
rpiotro
Active Member
I'll be darned. Yes, it is. That is what I get for believing unconfirmed *sugar* on the internet.
If after what I wrote, with graphs and math, and physics equasions, all you can refer to is stall current of a motor, with no reference to voltage or power, then we're in full agreement that there is no reason to carry on this conversation about how it makes sense to limit vehicle top speed because of how battery power just goes up as you go faster.
I did realize that I forgot to include the Plaid power curve that is published by Tesla. As you can clearly see, the maximum power is both at 0 RPM and at the highest speed like you said, not at 50 MPH like I said, and it makes perfect sense to limit top speed since the battery has to put out so much more power as the car goes faster.
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Fun other gearing fact that Elon lies about at the internet misunderstands: The Plaid motors turn slower at 200 MPH than the Model 3P does at 162 MPH or a 2014 Model S did at it's Top speed.
Carbon overwrapping has nothing to do with the ability to spin at high RPM, it's all about maintaining small gaps to keep power at those RPM's.
MikeRTX
Member
That's it, isn't it? I honestly don't care about people who do silly stuff. What happens to them is their own fault, and good riddance. But it's when they affect other people that I do care.
Go 200mph if you want to, but if you kill some innocent family just going to the grocery store or to visit grandma, there's no punishment good enough.
I've done some silly stuff in my day, but thankfully I survived, and I didn't affect other people doing it.
You can look at motorcycle helmet laws across the USA and see that American society doesn't agree on this either though. Single vehicle and person accidents and medical care do cost society in many ways.
The reason I started with stall current is because it is the most basic construct of the conversation you're trying to have. If you don't understand that, every variable mentioned after, is irrelevant.
When you consider things beyond that, you have to look at aerodynamic drag, which is not linear and can more than double at 250kmh than it is at 200kmh. Then you calculate in rolling resistance increases both due to increased downforce and increased and general speed. Then you need to have interference considerations on the motors, gearbox and drivetrain resistance.
And not a single one of those variables matter unless you also consider metrics of controller programming because of Hz and amperage modulation.
That is why I ignored the conjecture in your extensive post. Just because you see say 500hp output at 5000rpm and 350hp at 10000 rpm does not mean there's more power draw at 5000rpm.
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I accidentally put two separate conversations in this post - ignore the part about drag and resistance. That was intended for a different discussion on top end power.
That was the joke. The only way to make a Plaid draw max power at 0 MPH and 200 MPH was to turn the graph upside down.
And the reason I keep talking about power, not stall current, is because you are claiming that the battery sees max draw at high speeds. I am well aware of stall currents. I design electric vehicles for a living. You can clearly see that the POWER out of the battery is basically zero at zero RPM. This is because the battery doesn't care about MOTOR current. The battery cares about motor POWER. The inverter converts between voltage and current as needed, but power is power.
You're falling into the trap that motors generally can do maximum TORQUE at zero RPM. But zero RPM is zero power. So the battery flat out doesn't care. Which is exactly why every graph of a Tesla's POWER ramps up from zero- because it has flat torque to not spin the tires, but the RPM is increasing, and thus the power must increase linearly with RPM.
The fact that you don't get this is actually the most basic construct of the conversation were trying to have, which I will remind you started with this:
This is an illogical statement since above ~60 MPH, all Teslas draw LESS POWER from the battery as they go faster. There is never a reason to limit top speed for the battery's sake since the battery is not loaded more at higher speeds.
Now you're really off into facts don't matter land.
HP is power. Horsepower and Watts are the same thing, and conservation of energy is a thing. You can't say 500HP is not 500HP.
Read what you wrote. You just said just becuse you have 500HP at 5K RPM and 350HP at 10K RPM doesn't mean you have 500 HP at 5K RPM. This is just completly wrong and self conflicting. Where is this magic power coming from that allows you to get 500 mechanical horsepower with 350 HP of electrical draw? The ONLY PLACE the power comes from is the battery. There is zero difference between mechanical HP and electrical power in an EV because the systems are so efficent and linear. So your only possible argument here is that the motors are massivley inefficent at 500HP/5K RPM but much more efficent at 350HP/10K RPM? There's just no evidence that is true.
Remove the RPM from your statement because it's irrelevant. Power is power, that's the point. 500HP can be at any RPM. So you can't say 500HP is 350HP isn't 500HP. You're all screwed up because you're used to ICE cars with torque curves and transmissions and you never actually think about fuel flow in an ICE engine, you only care about mechanical output power and not conversion efficency.
Some very serious D-K occuring here.
Also, I did notice that you completely ignored my very simple math that 1000HP for 9.3 seconds is 1,930 watt hours, and for 15.2 seconds it's 3,150 watt hours, and that's nowhere near 7% of a 97kWh battery, and for this to happen you'd need an insane change in motor and inverter effieceny between 150 MPH and 175 MPH (and this has nothing to do with any other drag source outside of the drivetrain, that is where the energy goes and limits the speed of the car)
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I know you have me on your ignore list so you won’t read this but you seriously don’t understand what you are talking about at all.
When someone demonstrates how you are wrong you just pretend like their facts and evidence don’t matter. You put them on your ignore list and then pretend they don’t exist and keep on peddling your “alternative facts”.
Try considering that you could be wrong sometimes. Try listening to what Gearchruncher is explaining with evidence and logic to back it up. Well that and a heaping of sarcasm when it is warranted.
You aren’t correct about this and yet you refuse to look at it any differently. And yes, I have done that in the past too. I am guilty of it just the same. However, I also can admit when I am wrong and learn from it. Can you?
Oh cool, then you should be able to easily explain what caused the electrical fire on this bot a few days ago?
No good engineer would definitivley tell you why a battlebot caught on fire from a single video like that, but also not sure what that has to do with this discussion at all? Seems like you trying to change the topic away from simple EV motor and battery physics?
It has to do with what you keep saying is irrelevant. Stall current caused this fire when the weapon stopped and the motor was still attempting to spin at full power but could not.
It's actually pretty simple and any mediocre engineer could deduce if they have experience with electric motors.
