Tesla Model S Versus Airplane

[Snowdog]

Tesla's motors had a problem with overheating when pushed. When they removed the transmissions it made the situation worse.

ONLY for very small motors with little torque can you achieve such RPMs. For big motors you are limited.

Trust me on this. I deal with big HP PWM electric motors every day attached to fans. I see all kinds of issues. Running a motor at it's max rated RPM is hard on it in the long run and causes them to heat up quickly. It wears out bearings faster, and generates static electricity which can damage the shaft if it's not properly grounded.

Heat = total input power - received mechanical power. Motors are NOT 100% efficient. Well into the 90% range, but not 100%.

No I don't trust you. Electric Motors aren't 100% efficient. But the losses are primarily electrical, not mechanical. Take your 90% EV motor.


10% of 400KW = 40 KW of heat.
10% of 200KW = 20 KW of heat.

RPM isn't the issue, it is the input power. You can run an unloaded EV motor at near it's maximum RPM all day, it won't over heat.

Unload you could probably reach full RPM with less than 10 KW.

10% of 10KW = 1 KW of heat.

Sad that you deal with big PWM motors and don't even understand the fundamentals.

 

[Deleted member 93354]

ONLY for very small motors with little torque. For big motors you are limited.

No I don't trust you. Electric Motors aren't 100% efficient. But the losses are primarily electrical, not mechanical. Take your 90% EV motor.


10% of 400KW = 40 KW of heat.
10% of 200KW = 20 KW of heat.

RPM isn't the issue, it is the input power. You can run an unloaded EV motor at near it's maximum RPM all day, it won't over heat.

Unload you could probably reach full RPM with less than 10 KW.

10% of 10KW = 1 KW of heat.

Sad that you deal with big PWM motors and don't even understand the fundamentals.

there's load resistance and mechanical resistance. Not all heat is generated from load resistance. And with all things mechanical the faster you spin them the more heat you generate. With large high rpm motors this becomes an issue. It is NOT insignificant. Granted motors are even less efficient (PF) at lower RPMs but when you really push the high end under mechanical inefficiency does take a toll. I don't have access to Tesla's motors to test them. But running ANYTHING at high RPM will cost you eventually. Your assumptions are that motors are perfectly balanced. They aren't. Castings and windings are not perfectly placed, and bearings 100% true without friction. Even roller bearings have friction. Centrifugal forces for this imbalance increase exponentially as speed increases. mV*V/R. This doesn't even account for friction.

A good motor designer will set the design cap before these factors come into play and say rated RPM = XYZ. After that he knows the efficiency will drop. However when dealing with wide RPM range high horsepower, high torque motors sometimes you can't. Efficiency drops off once you reach a certain point and rather drastically. So for standard motors where properly spec'd this isn't an issue.

And you can use cold rolled steel, or cast. But then you have to weigh in the cost, advantages of weight and size and heat dissipation properties.

Sure you can keep motors small. Sure you can keep them light weight. Sure you can keep their cost down. You can make them small and spin them faster, But their efficiency drops when you do such things. Guess where size, cost and weight matters? Yep cars.

At this point we will have to agree to disagree.

 

[Snowdog]

there's load resistance and mechanical resistance. Not all heat is generated from load resistance. And with all things mechanical the faster you spin them the more heat you generate. With large high rpm motors this becomes an issue. It is NOT insignificant. Granted motors are even less efficient (PF) at lower RPMs but when you really push the high end under mechanical inefficiency does take a toll. I don't have access to Tesla's motors to test them. But running ANYTHING at high RPM will cost you eventually. Your assumptions are that motors are perfectly balanced. They aren't. Castings and windings are not perfectly placed, and bearings 100% true without friction. Even roller bearings have friction. Centrifugal forces for this imbalance increase exponentially as speed increases. mV*V/R. This doesn't even account for friction.

And its insignificant in electric car motors which don't need to go over 16 000 RPM. You can run piston racing engines up to 20 000 RPM. The smoothest piston engine in the world is a jackhammer compared to electric motor.

It's also trivial to balance something that has a symmetrical design and just rotates in a circle. Sure there will slight imbalances in manufacturing, but you correct the final product on a balancing machine.

At this point we will have to agree to disagree.

Thats about the only thing we agree on.

 

[haste.]

Who the hell does that in a Honda CRV? The only thing slower than a CRV is a Prius.

Yeah man, things like that actually happened fairly often. I was driving a Vette on the same strip and a brand spanking new Mazda 6 pulled up, same shit. Just kids thinking their 4-bangers are fast.

 

[Tsumi]

And its insignificant in electric car motors which don't need to go over 16 000 RPM. You can run piston racing engines up to 20 000 RPM. The smoothest piston engine in the world is a jackhammer compared to electric motor.

It's also trivial to balance something that has a symmetrical design and just rotates in a circle. Sure there will slight imbalances in manufacturing, but you correct the final product on a balancing machine.




Thats about the only thing we agree on.

I have read articles (freely accessible through simple searches on the internet) that a properly designed transmission for an EV can increase its efficiency by up to 15%.

I don't know about you, but that's a fairly solid indication to me that electric motors are not 90+% efficient across the large part of its rpm range. Obviously some businesses see a market in EV transmissions, as Drive System Design recently came out with their MSYS system.

 

[Snowdog]

I have read articles (freely accessible through simple searches on the internet) that a properly designed transmission for an EV can increase its efficiency by up to 15%.
.

The only ones I have see have been done by transmission manufacturers.

No one doing an EV is using a transmission, if you could get 15% more range with a transmission, companies would do that.

I doubt you will ever see any major player use a transmission in an EV, because in reality, adding a transmission would cost you some efficiency, and you are starting a deficit. You need to assume a lot of motor inefficiency to get it back and make headway.