Mach E GT 70+ Acceleration Issue - Video

[Brofessional]

Yes it does, it just extends the point at which the torque loss occurs. It still happens, and its a sharp drop off.

Tesla and other manufactures run a second motor that isn't a PMSM so they are better able to transition power over at high speeds. Porsche has 800V batteries so they can push higher drive voltages to overcome the back EMF. Everything I've seen with my car and others here just look like the torque drop off of a bldc motor.

Good god.

hp = T x rpm/5252

Torque drops because power is held constant. It does not fucking matter why it's held constant.

Plaid is PMSM. Model 3 is PMSM. Induction on earlier/other Teslas was/is 100% for efficiency. Induction shits the bed at high rpms unless you increase costs exorbitantly for cooling.

In case anyone else is looking for a decent barometer of whether or not a contributor knows what they're talking about, back EMF is a good candidate. If they start talking about "back EMF" as an explanation for why modern EVs "don't accelerate like ICE" or some shit, they don't know anything about EM field generation.

Back EMF is part of the equation for PM motors, and that's the point. That shit is a known value before a single prototype is produced, and the units are designed around it. Advancing technologies like PMSM and rotor design to alter those values are fascinating, but that's very early design phase stuff. Talking about back EMF as a reason for why your mach e isn't as fast as you expected makes about as much fucking sense as a C8 owner blaming their lack of drag strip prowess on 91 octane.

 

[iankellogg]

Good god.

hp = T x rpm/5252

Torque drops because power is held constant. It does not fucking matter why it's held constant.

Plaid is PMSM. Model 3 is PMSM. Induction on earlier/other Teslas was/is 100% for efficiency. Induction shits the bed at high rpms unless you increase costs exorbitantly for cooling.

In case anyone else is looking for a decent barometer of whether or not a contributor knows what they're talking about, back EMF is a good candidate. If they start talking about "back EMF" as an explanation for why modern EVs "don't accelerate like ICE" or some shit, they don't know anything about EM field generation.

Back EMF is part of the equation for PM motors, and that's the point. That shit is a known value before a single prototype is produced, and the units are designed around it. Advancing technologies like PMSM and rotor design to alter those values are fascinating, but that's very early design phase stuff. Talking about back EMF as a reason for why your mach e isn't as fast as you expected makes about as much fucking sense as a C8 owner blaming their lack of drag strip prowess on 91 octane.

except tesla doesn't use a normal PMSM motor, they run them in PMSM at low speeds and switch to SRM at high speeds.

Flux weakening also does LOWER the power and efficiency. You're talking mechanical power, i'm talking electrical power. Flux weakening extends the constant power region but that's constant electrical power, the efficiency starts to fall off, and near the top of the rpm range there is nothing left for torque or power. The back EMF is just too high to be able to dump more current into the motor.

 

[pt19713]

except tesla doesn't use a normal PMSM motor, they run them in PMSM at low speeds and switch to SRM at high speeds.

FYI on the 3/Y, it's not speed dependent but more so power (as needed) and/or traction that will dictate when the front induction motor is activated. Below is a graph on a datalog on did last winter showing when the front induction motor activates. On this 33 minute drive, it only activated about 15 times once the accelerator was at about 30%. Not shown here is when the front motor activates when the rear end detects slippage. The 3/Y dual motor is 100% RWD (permanent rear magnet) regardless of speed.

 

[Mach1E]

except tesla doesn't use a normal PMSM motor, they run them in PMSM at low speeds and switch to SRM at high speeds.

Flux weakening also does LOWER the power and efficiency. You're talking mechanical power, i'm talking electrical power. Flux weakening extends the constant power region but that's constant electrical power, the efficiency starts to fall off, and near the top of the rpm range there is nothing left for torque or power. The back EMF is just too high to be able to dump more current into the motor.

I feel like a picture is worth 1000 words.

Tesla P85 dyno. Horsepower is almost completely flat:

 

[blue92lx]

except tesla doesn't use a normal PMSM motor ...

I feel like this whole forum is running on a PMS motor

 

[Olds442]

I feel like this whole forum is run on a PMS motor

 

[blue92lx]

Seriously though can't someone get a dyno in? lol, maybe the forum can do a gofundme to cover the cost, it would answer soooooooo many questions. Just do like a full run, a 0-60, 50-70, 70-100. Send us the sheets, and we could pretty much just shut off macheforums.com after that happens.

 

[harrysiii]

Seriously though can't someone get a dyno in? lol, maybe the forum can do a gofundme to cover the cost, it would answer soooooooo many questions. Just do like a full run, a 0-60, 50-70, 70-100. Send us the sheets, and we could pretty much just shut off macheforums.com after that happens.

What's the fun in that??!

 

[physib]

Is he still around? Just use the ignore function and you won't see each other.

 

[blue92lx]

What's the fun in that??!

I guess we wouldn't have anything to talk about if someone did go to a dyno lol

 

[Brofessional]

except tesla doesn't use a normal PMSM motor, they run them in PMSM at low speeds and switch to SRM at high speeds.

Flux weakening also does LOWER the power and efficiency. You're talking mechanical power, i'm talking electrical power. Flux weakening extends the constant power region but that's constant electrical power, the efficiency starts to fall off, and near the top of the rpm range there is nothing left for torque or power. The back EMF is just too high to be able to dump more current into the motor.

It sounds like you're suggesting the efficiency loss with flux weakening is what GT owners are seeing at like 6-7k rpm, and it's just not. Meaningful, perceptible mechanical power reduction secondary to flux weakening efficiency losses should occur well beyond everyday speeds with a 9.05 gear ratio unless Borg Warner's EEs are bad at math.

But we already have plenty of data from RWD only units to know torque/power curves look like they should, which is why when you asked if flux weakening is why we're seeing what we're seeing in the GTs I said no. This has been discussed ad nauseum in multiple other threads.

I assure you I know the difference between mechanical power and electrical power. I work with high magnetic field generation. And despite EVs being the first sort of ubiquitous public exposure to this stuff, electric motors have been around for centuries and are mathematically much simpler than ICE designs (of which you're probably aware). Mechanical torque and power for the BW unit was calculable throughout the rev range before a single unit was ever produced, which means how that rev range feels in the vehicle was also predictable notwithstanding negligible future design differences in weight, aero, and rolling resistance.

As an aside, technically Tesla is using IPM synRM, which isn't new. Toyota has been using it in the prius since before Tesla was even a sparkle in Elon's eye. Admittedly Tesla's rotor design is probably the most elegant in the industry.

 

[phil]

I feel like this whole forum is running on a PMS motor

Sounds like a source of limitless energy. Take that, OPEC!

 

[Mach1E]

Sounds like a source of limitless energy. Take that, OPEC!

True, but unfortunately that energy is so powerful that all you do is spin your wheels and go nowhere.

It does on rare occasions allow you to drive in circles. And once or twice it was used to beat a horse. Unfortunately that horse was previously deceased.

 

[Frankie]

Does yours not have the power meter on it? You keep talking about how it feels but you've never once said 'you can see on the power meter it drops at X speed'

The video posted here has put all of these 'it feels like' comments into a data situation that we can see what's happening which is a huge difference.

I drive a car, not a gauge. It's great that the gauge confirms what we already knew from dragy times but the dragy times and how the car feels is what is important, not what a gauge (that's programmed by Ford) says.

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