Macan turbo 0-60 times not matching specs

[daveo4EV]

Sorry, a good part of this is just not true at all. I have an EE background. While the basic math here is sound, if you want to adjust power output you can easily do this via voltage regulation.

In your simple single cell example, we commonly slap 3.3v regulators in front of lithium cells to run low power electronics, which keeps the voltage and power usage consistent and as expected across nearly the full range of the battery capacity.

We sometimes use buck or boost converters to adjust voltage to where a load needs it to be. There are many ways to manipulate power delivery, we don’t need to naively follow a simple discharge curve.

I don’t know much about the specifics around EV power. I’d assume though that there is some power conditioning and conversion going on to tailor the power to the load. I’m not even sure EV motors are DC, they’re always talking about silicon carbide inverters.

most EV motors are AC - I'd love to hear more - so from an EE perspective 3.3v regulator will keep the each cell at 3.3 volts for "discharge_ but how to compensate when the cell drops below 3.3 v for discharge…

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[PrudentOcean]

You can boost the voltage with a current amplifier.

 

[sor]

most EV motors are AC - I'd love to hear more - so from an EE perspective 3.3v regulator will keep the each cell at 3.3 volts for "discharge_ but how to compensate when the cell drops below 3.3 v for discharge…

That’s when you effectively run out of power. In fact if the regulated output is 3.3v, you will probably require a bit more to keep it running, say 3.35v. So you end up with the last 3% or so of the battery as unusable, but it wouldn’t be usable anyhow at such low SoC and voltage.

A regulator doesn’t keep the cell at a voltage, it sits in between and outputs a consistent voltage even though the input varies.

You also have to deal with the internal resistance of the battery going up as it discharges, which effectively limits the current that can be output. It wouldn’t help to add a boost converter when the battery voltage drops at low SoC because the current it can provide at that point is going to be limited.

In the end you’re designing the battery and load such that the battery can handle the power requirements put on it throughout the operable range of the battery, and power conditioning is a part of that matching source to load. At least that’s how I’m familiar with designing electronics.

 

[daveo4EV]

Did you mean 3.3 mi/kWh instead of 3.3 kWh/mi?

I would love my Macan to only consume 3.3kWh in an hour going at 65mph. That would mean I could drive (95 / 3.3) * 65 = 1,871 miles with a single full charge.

Conversely, a 3.3 kWh/mile would mean I could only drive 28 miles on a full charge.

yeah you got me...my average consumption is about 3 to 3.3 miles/kWh

 

[jwatte]

How I have learned it, from other people are are closer to these circuits:

The #1, #2, and #3 problem in electric drivetrains is efficiency. More efficient means both longer range, AND less need for cooling, so you can jam more power into the same volume/weight.

While the car motors are "AC," they are "AC" in the sense that a controller changes the electric field inside the motor by switching current into the coils. This is nice because there are no brushes to wear out. The counter-field comes from induction currents (SAC,) magnets (IPM) or magnets (BLDC) unless you use an electrically excited motor like Renault ... which adds back the brushes! (Another good comparable is the spindle drives used for machine tools.)

Anyway, all that being said -- a linear regulator, or any regulator, has losses. There will be at least a few hundred millivolts of drop-out on that 3.3V regulator, which will reduce efficiency by something like 10%, which is entirely a no-go for anything where battery runtime and cooling matters.

The same approach happens in the motor controllers and inverters for these vehicles. The inverters/controllers are there to run the inductors, basically like large H bridges with PWM. Run the PWM at high enough frequency and the inductance in the motor works as your current moderator! Just modulate the duty cycle for how much you want current to flow backwards or forwards. I would not expect a separate boost converter in the power path, to try to boost voltages to a standard voltage (nor, worse, a buck converter) simply because it'll add more losses and more components, for no real gain -- the current through the motor is already modulated by the PWM and the winding inductance.

For 90% of the range of the throttle, "top of charge" versus "bottom of charge" wont' really matter much, because the PWM duty cycle isn't hitting flat-out maximum, so the difference in ability to overcome inductance and drive current into the windings doesn't matter.

This is why the peak power comes at top charge of the battery, because the voltage that the motor sees is the highest, which means that when the PWM is running at full duty cycle, the most current can flow through the windings. (Battery performance is also the highest, if you end up being internal resistance limited.)
Similarly, a higher voltage also overcomes more back EMF, which is the main speed limiting force in these electric motors, so the maximum RPM of the motor will go up a little bit when run at full charge.

 

[alvaro]

I have launched my Macan Turbo many times, but just recently attempted to track the 0-60 times. I’m only getting 4 seconds plus times using the race stats app for iPhone. Should I launch with traction control on/off.

what am I missing?

I wouldn't even attempt this. But I guess if you have 5 cars ....

 

[sor]

How I have learned it, from other people are are closer to these circuits:

The #1, #2, and #3 problem in electric drivetrains is efficiency. More efficient means both longer range, AND less need for cooling, so you can jam more power into the same volume/weight.

While the car motors are "AC," they are "AC" in the sense that a controller changes the electric field inside the motor by switching current into the coils. This is nice because there are no brushes to wear out. The counter-field comes from induction currents (SAC,) magnets (IPM) or magnets (BLDC) unless you use an electrically excited motor like Renault ... which adds back the brushes! (Another good comparable is the spindle drives used for machine tools.)

Anyway, all that being said -- a linear regulator, or any regulator, has losses. There will be at least a few hundred millivolts of drop-out on that 3.3V regulator, which will reduce efficiency by something like 10%, which is entirely a no-go for anything where battery runtime and cooling matters.

The same approach happens in the motor controllers and inverters for these vehicles. The inverters/controllers are there to run the inductors, basically like large H bridges with PWM. Run the PWM at high enough frequency and the inductance in the motor works as your current moderator! Just modulate the duty cycle for how much you want current to flow backwards or forwards. I would not expect a separate boost converter in the power path, to try to boost voltages to a standard voltage (nor, worse, a buck converter) simply because it'll add more losses and more components, for no real gain -- the current through the motor is already modulated by the PWM and the winding inductance.

For 90% of the range of the throttle, "top of charge" versus "bottom of charge" wont' really matter much, because the PWM duty cycle isn't hitting flat-out maximum, so the difference in ability to overcome inductance and drive current into the windings doesn't matter.

This is why the peak power comes at top charge of the battery, because the voltage that the motor sees is the highest, which means that when the PWM is running at full duty cycle, the most current can flow through the windings. (Battery performance is also the highest, if you end up being internal resistance limited.)
Similarly, a higher voltage also overcomes more back EMF, which is the main speed limiting force in these electric motors, so the maximum RPM of the motor will go up a little bit when run at full charge.

Yeah, I’ve used H bridges to control smaller motors. I wouldn’t expect them to use a linear regulator or something simple like voltage divider, agree it would be too inefficient.

From what I’ve found researching, the EV motor controllers contain something called a traction inverter, which is a switching converter that acts like both an H bridge and a DC-DC switching supply. Part of its role is to perform the regenerative charging which also involves voltage conversion.

I guess that makes sense because a switching power supply and an H bridge do similar things and contain similar components. In fact if I recall, the input side of a switching supply is often an H bridge (or a configuration close to it in form and function). I can imagine you could use the switching from a DC-DC to drive something via PWM but it probably isn’t as simple as just leaving the rectifier off the back end.

This traction inverter and its control system condition the power to keep the output to the motor smooth and consistent throughout the range of the battery’s operating voltage.

If you watch a lot of EV videos they sometimes make a big deal about whether the inverters are silicon carbide or not, like when influencers meet with Rivian engineers. This improves efficiency of the conversion, some claim up to 99% efficiency

 

[MVO]

Check your "G" meter if you have one, for 0 to 60 mph
0.6 G = 4.58 sec
0.7 G = 3.93 sec
0.8 G = 3.44 sec

The lack of digits makes it a coarse check but my 4S reads 0.7, matching the spec

 

[dwc39]

Update: I charged the Macan to 100% and launched it. 0-60 time was 3.97s. This variance in time from advertised spec is closer to what I would expect with a simple iPhone app. Even at that time, the wheels spun out. I’m sure I can reduce the .87s on a better road surface.

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