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Does anyone know what Tesla did to solve low performance with SOC and Higher speeds?

scooby-snack

Member
Aug 25, 2018
68
78
California
I just picked up my Plaid a couple of weeks ago. Besides all of the the improvements the one that I'm most blown away by is the performance at low / lower SOC and of course the car pulls no matter the speed. It's hard to imagine that Ceramic Coating Motors, and improved cooling has essentially solved these previous issues. My 4 previous Tesla all suffered from the above mentioned massively.
 
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Zcd1

Member
Sep 2, 2018
749
907
Walloon Lake, MI / LaQuinta, CA
So you're saying that you don't believe that the things Tesla literally pointed out as making the biggest difference in performance at low SOC and high speeds are the reasons for the improvement???

Ohhhhkaaaay.....
 

GtiMart

Active Member
Nov 13, 2019
1,370
1,209
Quebec City, Canada
Performance at low SOCs in general seems limited by the pack. Its voltage is lower, which in itself means it cannot push as much peak power. Max amps seems to be held back in those situations too, possibly to protect the pack from going too low. I can think of a few reasons the Plaid could push harder at low SOCs. One, there could be a bigger bottom buffer, meaning at 0% SOC there is more energy left in the pack (higher voltage). That would mean a lower risk of "bottoming out the voltage", so the BMS might reduce max amps less drastically. Two, the pack has a higher voltage (450V instead of 400V). Assuming the motors require the same voltage, the pack voltage would still be high at low SOCs comparatively... Not sure here, I'm not an electrical engineer. Three, they made the BMS more tolerant to low voltage to extract full power but that is detrimental to the life of the pack...
All just extrapolations on my part, ideas to get the discussion going.
 
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n2mb_racing

Active Member
Jun 14, 2014
1,181
752
durham, NC
I've been wondering a related question. How did they flatten out the power curve out to 200 mph? It's insane. I imagine they increased the gear reduction a bit to allow the motors to spin faster, but the power should start dropping off as the motor back EMF approaches the battery voltage. How much faster are the motors spinning?

 
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strider

Active Member
Oct 20, 2010
3,627
997
NE Oklahoma
Let me start by saying that I am not an engineer, but I have driven Tesla's for 11 years :)

In this video:

They calculated the motor turns over 18,000rpm.

The problem with back EMF is that you need to increase the current the faster the motor goes. Say you have a simple 12V motor spinning and back EMF was 2V. So you had ad applied voltage of 10V. You want the motor to go faster so you increase to 14V. Back EMF increases to 3 so your applied voltage is 11V. Motor sill spin faster, but you had to put in 2V to get 1V applied to the motor.

So in the case of Plaid, I believe there was a battery chemistry change along with improved battery cooling that allows the pack to output more engergy for longer. So I believe they are simply throwing more power at the problem.

Also, I believe this is the first use of permanent magnet motors in Performance S/X. Permanent magnet motors have less back EMF than the AC Async motors that they used to use. But the PM motors are more sensitive to heat (the magnets melt), hence the carbon-sleeved rotors.
 
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scooby-snack

Member
Aug 25, 2018
68
78
California
Let me start by saying that I am not an engineer, but I have driven Tesla's for 11 years :)

In this video:

They calculated the motor turns over 18,000rpm.

The problem with back EMF is that you need to increase the current the faster the motor goes. Say you have a simple 12V motor spinning and back EMF was 2V. So you had ad applied voltage of 10V. You want the motor to go faster so you increase to 14V. Back EMF increases to 3 so your applied voltage is 11V. Motor sill spin faster, but you had to put in 2V to get 1V applied to the motor.

So in the case of Plaid, I believe there was a battery chemistry change along with improved battery cooling that allows the pack to output more engergy for longer. So I believe they are simply throwing more power at the problem.

Also, I believe this is the first use of permanent magnet motors in Performance S/X. Permanent magnet motors have less back EMF than the AC Async motors that they used to use. But the PM motors are more sensitive to heat (the magnets melt), hence the carbon-sleeved rotors.
Now that's what I'm talking about! What a great video and excellent explanation. Thank you so much!
 

n2mb_racing

Active Member
Jun 14, 2014
1,181
752
durham, NC
Let me start by saying that I am not an engineer, but I have driven Tesla's for 11 years :)

In this video:

They calculated the motor turns over 18,000rpm.

The problem with back EMF is that you need to increase the current the faster the motor goes. Say you have a simple 12V motor spinning and back EMF was 2V. So you had ad applied voltage of 10V. You want the motor to go faster so you increase to 14V. Back EMF increases to 3 so your applied voltage is 11V. Motor sill spin faster, but you had to put in 2V to get 1V applied to the motor.

So in the case of Plaid, I believe there was a battery chemistry change along with improved battery cooling that allows the pack to output more engergy for longer. So I believe they are simply throwing more power at the problem.

Also, I believe this is the first use of permanent magnet motors in Performance S/X. Permanent magnet motors have less back EMF than the AC Async motors that they used to use. But the PM motors are more sensitive to heat (the magnets melt), hence the carbon-sleeved rotors.

That's a good video, but I also can't figure out why the 2019 Raven Performance torque is higher than plaid? It seems like maybe they didn't publish the right gear ratios for the plaid motors?
 

n2mb_racing

Active Member
Jun 14, 2014
1,181
752
durham, NC
There is some room left in the plaid for sure.
Maybe? It looks like they reduced the gearing ratio and then massively increased the current to the motors to maintain the same or slightly lower torque to the wheels. They might be up against the current limit of the motors or controllers. Once the HP curve flattens out, that is up against the battery limit. I think they are already pulling ridiculous discharge from the battery. 760 kW out of a 98 kWhr pack is a lot! That's higher discharge than any other battery they have done before. They will likely need a different battery technology to pull more from the battery. Likely, plaid+ will have that battery, and we'll see another HP boost.
 

n2mb_racing

Active Member
Jun 14, 2014
1,181
752
durham, NC
My $0.02 is that this is it until they roll out the 4680s.
Yup. They need to pack in more batteries to enable higher discharge power, without sacrificing range. It seems that they tweaked the cell chemistry to allow higher discharge and sacrificed a little bit of capacity in the process (100 kWhr to 98 kWhr). They could go further and sacrifice a lot of range to pull massive power (like Samsung 25R cells or other power tool 18650 cells), but I don't think anyone would want that.

Then again, how much more power do we need?
 

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