View Single Post
Old 04-22-2021, 04:37 AM   #9 (permalink)
Join Date: Nov 2017
Location: Australia
Posts: 2,060
Thanks: 107
Thanked 1,605 Times in 1,136 Posts
Originally Posted by planetaire View Post

So I see that I have to give more explanations.
We are in 2021 talking about the Model S motor at 105 mph.
In my previous post I put a link where it can be seen that this motor is a permanent magnet motor.
Yes, previously, the main TMS motor was a induction one.
TM3 as also a PM motor in the rear (The only motor if 2WD). They only use induction for front when 4WD. In the previous model S there where 2 induction motors and the car choose the front or rear during driving in order to improve the range, but that was the past.

Aerohead said : 197.6 hp at 105 mph. I use electric units, so rounded 150 kW. No need to use two motor, a 2WD model can have this speed. Most of the rear motor have somewhat twice or more the power needed at 105 mph. This exact power value is not important I will compare the two motors/engine.

Then what are the motor losts at that power ?

Please look at this graph which is a pm exemple:

I don't have the exact Tesla PM graph. But it will be used at less then half the max power, at max rpm that mean less then half the torque. In this exemple the motor is still at his max efficiency. A induction motor too ! look at the insidev exemple
The difference is that the Tesla pm motor have 97% efficiency and the induction 93%.

The previously 7% losts become 3% ! That is a very important reduction.
Why not reduce the cooling air intake/out ?
Are Ice able to reduce there losts with a so big percentage, at max speed ?

And with Ice we don't talk about the same losts.
150 kW mean with a good engine (40% efficiency) 375 kW thermal.

What about Ice engines ?
30% losts in the radiator (And a lot via the tailpipe and so on)

Now compare 4% of 150 kW with 30% of 375 kW
That is 6kW and 112 kW. The ratio is 18.6. That is huge

Of course it would be a good idea to compare cooling possibilities : delta T, between out air and coolant will not be the same.
That is true, but one more time do some math.
I don't have all the Tesla S data, of course.
I will then take a very old design, with my car. Interesting because being a hybrid car I have both the ice coolant max temp and the Electronic/motor max coolant temp.
The Ice is used somewhere between 85 and 90 C, after the start which need several minutes. At 95C the electric fans come on. It is not a good idea to go over 100C
The electronic/motor coolant is used at very low temp. There is not a theresold like ice. But I never go over 65C. The max allowed is 75C. It is because igbt, the motor can have much more, the first problem would be magnets an after wire insulation.
My car have a very old design, more then 20 years old with igbt, not sic.
Sic are better in thermal management.

So I will take the max temp seen last year Here in my country, 40C. (You can do math with your's too)
The delta T is 60C for Ice and 35C (That is for Igbt, Sic are better). Ratio 1.7

Is it necessary to compare to the 18.6 ratio.between the energy to dissipate ?

Ice is more then 10 times difficult to cool.

More complex ? Different. For exemple the battery could need heating/cooling, but a turbo would need air cooling and so on, exhaust pipe need special thermal screens, special care near the tank ...

I totally agree.

For a more global idea about this car losts, you would add 3% losts in transmission, more for ice.

If you drive a long time you will have to handle the battery losts, say 1,5%.

And thats all great. Trouble is, on the only two BEV cars for which we have percentage cooling drag measurements (percentage of overall aero drag) the cooling drag values are in fact high! Not theory - actual measurements.
  Reply With Quote
The Following User Says Thank You to JulianEdgar For This Useful Post:
aerohead (04-23-2021)