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Old 04-21-2021, 12:23 PM   #1 (permalink)
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engine 'power' and cooling load

Example:
2012 Tesla Model S
* original Cd 0.26
* frontal area= 25.8333-sq-ft ( 2.4 meters -squared )
* 4,197- pounds, EPA test weight
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* @ 155-mph, aerodynamic load is 170.7366- hp ( top speed )
* @ 155- mph, rolling-resistance is estimated 26.8693- hp
* @ 115- mph, total road-load horsepower is est. 197.6059-hp
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* @ 85-mph, aero load is 28.1571-hp ( fastest legal speed in USA )
* @ 85-mph, R-R is estimated 14.7348-hp
* @ 85-mph, total road-load horsepower is est. 42.8919- hp.
--------------------------------------------------------------------------------------
* @ top speed, the 'engine' power requirement is 460% higher than at maximum legal speed.
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* @ top speed, 'engine' heat flux is 460% higher than at maximum legal speed.
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* @ top speed, 'engine' and battery cooling load is 460% higher than at maximum legal speed.
--------------------------------------------------------------------------------------
Had the Tesla Model S been specified for a lower top speed, it follows that, if it requires an 8%-drag cooling system for 155-mph, the Model S could easily have an adequate cooling system, with a fraction of 8% drag.
Ditto for Porsche's Taycan Turbo, and Turbo S, of 161-mph top speed.
------------------------------------------------------------------------------------
And since modern cars have ' multi-stage active cooling management of cooling...' , one would want to assign a 'spectrum' of cooling system drag, rather than a fixed value, like 8%.
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Additionally, as already mentioned by members, back-to-back comparisons between ICE and BEV variants of the same vehicle, offer the greatest insight into the difference in drag, including cooling drag, between any models of interest.
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Finally, I'll leave 33.333% of the argument unmentioned for the time being. Just to see if any of the 'experts' pick up on it ( be careful who you trust ).

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Old 04-21-2021, 12:30 PM   #2 (permalink)
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Slight issue:
Electric drivetrains get less efficient at high power.
460% mechanical power output means far more than 460% waste heat.
Also the Model S can't maintain topspeed, it overheats when going faster than about 210 km/h while the Taycan can maintain topspeed without overheating.
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Old 04-21-2021, 01:35 PM   #3 (permalink)
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slight issue

Quote:
Originally Posted by Autobahnschleicher View Post
Slight issue:
Electric drivetrains get less efficient at high power.
460% mechanical power output means far more than 460% waste heat.
Also the Model S can't maintain topspeed, it overheats when going faster than about 210 km/h while the Taycan can maintain topspeed without overheating.
Appreciate the info. Perhaps, over time, these sorts of specific quanta will be more widely available to the mortal man. I welcome it.
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Old 04-21-2021, 04:31 PM   #4 (permalink)
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Motor and electronic are excellent in Tesla. Better with values:
The last Tesla S motor have 97% efficiency
This efficiency decrease mainly during very low loads and/or very low speed.

In Tesla car you have Sic (Tesla is not the only, others bev have too)
Sic have 99% efficiency look at 40mn in the video

Total is 4% losts.

Not necessary to compare with ice losts, is it ?
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Old 04-21-2021, 05:20 PM   #5 (permalink)
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The 99% efficiency is for the inverter alone, not the entire drivetrain.

The efficiency of electric motors drops at high power outputs.
Especialy with induction motors like tesla runs.
It is true however that efficiency also drops at super low power output.
It's not that much overall, but going from 99% to lets say 90% means 10x the load on your cooling system for a given power output, however we're talking about topspeed at 197,6 hp vs cruising at 42,9 hp aka 4,6x as much.
So the thermal load might not be 4,6x as much, but 46x as much.

The drop to 90% is just an estimate, but I guess you see the issue.

With ICEs you have a lot higher losses, but a lot of them dissapear through the exaust and the rest is at a high temperature, wich requires less cooling air to get rid.

Anyway, EVs need a more complex thermal management system including but not limited to adjustable air intakes to reduce or even eliminate cooling drag when possible and provide maximum cooling capacity when required.
I see no reason why an EV should have any cooling drag at all when it's freezing and you're not driving fast.
The passengers greatly appreciate the waste heat in that scenario.
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Old 04-21-2021, 05:38 PM   #6 (permalink)
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Quote:
I see no reason why an EV should have any cooling drag at all when it's freezing and you're not driving fast.
The passengers greatly appreciate the waste heat in that scenario.
Someone like Elon Musk might conjur something like the Octovalve.
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Old 04-21-2021, 05:49 PM   #7 (permalink)
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That is one part of what is required.
In addition to it the air intakes as well as outlets should be variable as for cooling drag the temperature of the radiator is neglectable in our use cases.
(Yes, Meredith effect exists, but not in our cars at our speeds)
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Old 04-22-2021, 02:56 AM   #8 (permalink)
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Quote:
Originally Posted by Autobahnschleicher View Post
The 99% efficiency is for the inverter alone, not the entire drivetrain.

The efficiency of electric motors drops at high power outputs.
Especialy with induction motors like tesla runs.
Hello,

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 ?

Quote:
It is true however that efficiency also drops at super low power output.
It's not that much overall, but going from 99% to lets say 90% means 10x the load on your cooling system for a given power output, however we're talking about topspeed at 197,6 hp vs cruising at 42,9 hp aka 4,6x as much.
So the thermal load might not be 4,6x as much, but 46x as much.

The drop to 90% is just an estimate, but I guess you see the issue.

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.

Quote:
With ICEs you have a lot higher losses, but a lot of them dissapear through the exaust and the rest is at a high temperature, wich requires less cooling air to get rid.

Quote:
Anyway, EVs need a more complex thermal management system including but not limited to adjustable air intakes to reduce or even eliminate cooling drag when possible and provide maximum cooling capacity when required.
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 ...

Quote:
I see no reason why an EV should have any cooling drag at all when it's freezing and you're not driving fast.
The passengers greatly appreciate the waste heat in that scenario.
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%.

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Old 04-22-2021, 04:37 AM   #9 (permalink)
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Quote:
Originally Posted by planetaire View Post
Hello,

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.
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Old 04-22-2021, 05:23 AM   #10 (permalink)
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No, for exemple Aptera have a negative cooling drag.

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