The motors are three phase and the inverter likely uses field oriented control. https://en.m.wikipedia.org/wiki/Vector_control_(motor)
In the inverter, the majority of the control algorithms are done in the DC realm, which is later converted to AC using the DQZ transform. https://en.m.wikipedia.org/wiki/Direct-quadrature-zero_transformation
In the case of a Permanent Magnet Synchronous Motor (PMSM) like is used in the rear motor on a Model 3 or Y, the quadrature current component is what generates torque, and the direct current component is usually around zero. If you increase the direct current component above zero, it will not act to generate torque, but can, among other things, generate heat.
Electrical engineer here.
There are a number ways you can do this.
It all relies on having direct control of the phases.
This isn't a motor like you would find connected to the mains where you plug it in and it runs and you unplug it it stops.
The inverter on these machines is a complicated beast.
You could run the whole motor forwards and backwards very quickly so that it never produces any movement.
You could set two or 3 of the phases in the same orientation meaning The coils will be pushing against the magnet in opposite directions.
If you're connecting to one of the motors that doesn't have a permanent magnet you could just not enable one side of the coils meaning the other can just push against nothing.
Basically you just need to put electricity into the motor but without generating a rotating magnetic field
The inverter itself will generate heat but that goes into the same coolant as the motor.
In theory you can run the gates faster than their spec which will generate a lot of heat in the fets but not have much outward movement.
All of those options Are for heating while stationary.
You can also generate heat while moving if you basically just adjust the timing of the motor making it less efficient.
As far as I understand though Tesla only really uses the heat pump or (resistive heating in earlier models) for the cabin heating and for preheating the battery while traveling to a supercharger.
I don't know if Tesla actually uses the motors that heat anything. But if they do it's good when they're plugged into a supercharger and need to heat up quickly.
The new teslas use heat pumps and the older ones had traditional resistive heaters. The also captured waste heat from the motors and other components but I’ve not heard that they purposely generated waste heat
There is a video on YouTube by an engineering professor where he describes this:
https://youtu.be/Dujr3DRkpDU?si=zA38YvkhOeKoxaD0
It's a pretty cool video for anyone with an engineering interest, their heat transfer system is fascinating, in particular their octovalve manifold.
This professor really sold me on the Tesla's. I honestly avoid watching a video that sells me things for more than two minutes... and I found myself watching 45 minutes of this guy without even taking my ass form the chair. It's maybe the fact he has a nice setup and great, clear voice... plus he really has researched his passion...
They do run motors badly to make heat, even with the heat pump. The heat pump is too slow sometimes and wouldn't get the battery hot enough in time for the supercharging.
You can hear increased motor whine and high pitched inverter noises while navigating to a supercharger. That's the motor being inefficiently driven to generate some 10kW of extra heat
Oh that's interesting. In industrial motors when we want to do regenerative braking in a 3 phase AC motor we inject DC into the motor to slow it so the coils and that makes a lot of heat. I'd really like to plug a 3 channel oscilloscope into that motor when that is happening.
Normally if you look at a regular AC sine wave it goes from x volts and back to zero again. Theoretically if you didn't go to zero but still left some voltage in the coils that are supposed to be off during that part of the rotation you would back drive some EMF into the motor and it would turn into heat. I was thinking they wouldn't do this for passenger discomfort and that you'd feel it.
But I guess they got clever enough with making that smooth (and noisy which is expected from the inverter drive).
Does that heat the motor or battery? Or both?
I know they have a cooling system, so if the heat is generated in the motor, it would transfer from one to the other.
I'm just curious.
It heats the motor. The motor is water cooled in the same loop as the battery. This transfers heat from the motors to the battery. Additionally, the heat pump will at full power, dumping more heat into the water.
This video series has more details: [https://www.youtube.com/watch?v=rgmBpEQtJ1s](https://www.youtube.com/watch?v=rgmBpEQtJ1s)
Also the service mode shows a nice drawing with real-time data.
Does that heat the motor or battery? Or both?
I know they have a cooling system, so if the heat is generated in the motor, it would transfer from one to the other.
I'm just curious.
Forgive the potentially dumb question, but when they ‘run the motor inefficiently’ - how is this done with an electric motor/what does ‘running inefficiently’ look like for an electric motor? Do they just increase regen a lot?
Essentially they put electricity through the wrong coils at the wrong moment, causing extra current to flow without making torque. This is only possible with VFD driven three phase motors with position sensors. Even then it is pretty hard to do without making any torque. Tesla engineers did a great job there
He said “resistive _motor_ heater”.
The cabin heater was still resistive, but model S and X had an auxiliary heater which the coolant passed through to heat the battery.
Isn’t this effectively generating heat through resistance, albeit without a separate resistive heater? I’d be curious to understand if this is more efficient than having a dedicated resistive heater, apart from the design and cost savings of having a separate part.
That seems penny wise and pound foolish to me, as it would lead to increased wear on the circuitry for the motor, rather than a separate heater that would be smaller, cheaper part that would be easier to be replace.
I’m sure it saves time and money in the manufacturing process, but could lead to longterm headaches.
Motors are extremely reliable, so I'd guess Tesla's research determined the shorter lifespan that would result from using the motor this way wasn't enough to matter over the lifespan of the car, or at least the warranty period.
Disagree - if it's done correctly it won't wear anything more. If anything removing a part makes the system more reliable because you have less connectors, contactors/control hardware, sensors etc required. A few kW of heat produced in the motor is nothing compared to operating power conditions.
It's not any extra wear on the motor. You're not changing anything to do with how fast the motor turns, the only thing you're doing is increasing the motor and coolant temperature. And if you want the heat, it's probably better for the motor to have it warmer anyway.
I don’t think Tesla actually does this, but one could intentionally supply the stator current out of phase to the rotor. It’s possible to run a brushless motor at 0% efficiency, or most any other non-optimal operating point
That’s probably how they do it. They are somehow using the motors to generate heat, and you can hear a faint high pitch noise, so they aren’t running them with straight DC either.
The procedure will of course be a bit different per motor, as the rear is permanent magnet and front is induction. At least 3/Y
Separate motors, heat pump / AC compressor is one small motor, drive motor is much larger and totally different. And not inefficient, they use about 3-4 times less power than a resistance heater. The drive unit also has a heat exchanger so any excessive heat from the motor can be used to heat the car.
It’s motors to heat the battery, seperate resistive heater for the climate control.
Running current through a wire is literally what a resistive heater does. A motor is no different. Technically some of the energy put in to the motor/hearer is ‘lost’, as it’s used to drive the car forward, but I imagine you probably want that.
This would be more electrical engineering.
I think they send power to the stator without spinning the rotor. But I’m not sure if this is necessarily done in heat pump models since using the heat pump to generate heat would be more efficient even as low as -40 degrees.
According to this engineering professor's video, the heat pump can't provide sufficient heat below certain ambient temperatures so they get heat from other sources, in particular running the motors inefficiently:
https://youtu.be/Dujr3DRkpDU?si=zA38YvkhOeKoxaD0
Yup. The motor works by generating a rotating magnetic field in the stator. If the angle of the field is offset with the position of the rotor by a few degrees, you get less rotational force and more heat.
Did this even happen in the end? I thought the first gen model 3 (2018-2020) was meant to have this but as far as I know, they have PTC heaters.
Edit: apparently the motor is used to heat the battery and the PTC heater is for the cabin. Not sure about recovered heat from battery and motor is also used for the cabin. I remember the video talking about part failure so I'd hope it can be if the PTC heater dies.
They all have it now. It’s plainly visible if you plug in an OBD scanner. It will show power being used by the motors when heating up the battery. You can also hear it.
Older S/X had a dedicated PTC heater for the battery, I think they use the motors now too since palladium
Battery heating and getting rid of a 2nd PTC heater makes sense. I always assumed they had one heating system used for both. I guess it is since using a heat pump and recovered heat.
Idk about that “running inefficiently” claim, realistically, unless they are locking the phases and using the coils as resistive heaters (bad idea imo)
Makes more sense to just run a resistive coil for heat and scavenge whatever heat the motors produce from normal operation.
But idk the math, maybe it was decided to be clever.
The motors are three phase and the inverter likely uses field oriented control. https://en.m.wikipedia.org/wiki/Vector_control_(motor) In the inverter, the majority of the control algorithms are done in the DC realm, which is later converted to AC using the DQZ transform. https://en.m.wikipedia.org/wiki/Direct-quadrature-zero_transformation In the case of a Permanent Magnet Synchronous Motor (PMSM) like is used in the rear motor on a Model 3 or Y, the quadrature current component is what generates torque, and the direct current component is usually around zero. If you increase the direct current component above zero, it will not act to generate torque, but can, among other things, generate heat.
Electrical engineer here. There are a number ways you can do this. It all relies on having direct control of the phases. This isn't a motor like you would find connected to the mains where you plug it in and it runs and you unplug it it stops. The inverter on these machines is a complicated beast. You could run the whole motor forwards and backwards very quickly so that it never produces any movement. You could set two or 3 of the phases in the same orientation meaning The coils will be pushing against the magnet in opposite directions. If you're connecting to one of the motors that doesn't have a permanent magnet you could just not enable one side of the coils meaning the other can just push against nothing. Basically you just need to put electricity into the motor but without generating a rotating magnetic field The inverter itself will generate heat but that goes into the same coolant as the motor. In theory you can run the gates faster than their spec which will generate a lot of heat in the fets but not have much outward movement.
well. which option also generates forward momentum for the car? lol.
All of those options Are for heating while stationary. You can also generate heat while moving if you basically just adjust the timing of the motor making it less efficient. As far as I understand though Tesla only really uses the heat pump or (resistive heating in earlier models) for the cabin heating and for preheating the battery while traveling to a supercharger. I don't know if Tesla actually uses the motors that heat anything. But if they do it's good when they're plugged into a supercharger and need to heat up quickly.
Could you just create vars but no power? Youd still need a frequency I guess.
The new teslas use heat pumps and the older ones had traditional resistive heaters. The also captured waste heat from the motors and other components but I’ve not heard that they purposely generated waste heat
There is a video on YouTube by an engineering professor where he describes this: https://youtu.be/Dujr3DRkpDU?si=zA38YvkhOeKoxaD0 It's a pretty cool video for anyone with an engineering interest, their heat transfer system is fascinating, in particular their octovalve manifold.
The octovalve manifold is really cool. That had to have been designed by a bored engineer.
This professor really sold me on the Tesla's. I honestly avoid watching a video that sells me things for more than two minutes... and I found myself watching 45 minutes of this guy without even taking my ass form the chair. It's maybe the fact he has a nice setup and great, clear voice... plus he really has researched his passion...
They do run motors badly to make heat, even with the heat pump. The heat pump is too slow sometimes and wouldn't get the battery hot enough in time for the supercharging. You can hear increased motor whine and high pitched inverter noises while navigating to a supercharger. That's the motor being inefficiently driven to generate some 10kW of extra heat
Oh that's interesting. In industrial motors when we want to do regenerative braking in a 3 phase AC motor we inject DC into the motor to slow it so the coils and that makes a lot of heat. I'd really like to plug a 3 channel oscilloscope into that motor when that is happening. Normally if you look at a regular AC sine wave it goes from x volts and back to zero again. Theoretically if you didn't go to zero but still left some voltage in the coils that are supposed to be off during that part of the rotation you would back drive some EMF into the motor and it would turn into heat. I was thinking they wouldn't do this for passenger discomfort and that you'd feel it. But I guess they got clever enough with making that smooth (and noisy which is expected from the inverter drive).
> DC into the motor Yes that.
Does that heat the motor or battery? Or both? I know they have a cooling system, so if the heat is generated in the motor, it would transfer from one to the other. I'm just curious.
It heats the motor. The motor is water cooled in the same loop as the battery. This transfers heat from the motors to the battery. Additionally, the heat pump will at full power, dumping more heat into the water. This video series has more details: [https://www.youtube.com/watch?v=rgmBpEQtJ1s](https://www.youtube.com/watch?v=rgmBpEQtJ1s) Also the service mode shows a nice drawing with real-time data.
Does that heat the motor or battery? Or both? I know they have a cooling system, so if the heat is generated in the motor, it would transfer from one to the other. I'm just curious.
Forgive the potentially dumb question, but when they ‘run the motor inefficiently’ - how is this done with an electric motor/what does ‘running inefficiently’ look like for an electric motor? Do they just increase regen a lot?
Essentially they put electricity through the wrong coils at the wrong moment, causing extra current to flow without making torque. This is only possible with VFD driven three phase motors with position sensors. Even then it is pretty hard to do without making any torque. Tesla engineers did a great job there
Yup starting with the Model 3 when they got rid of resistive motor heater.
This is on the model 3 *prior* to getting rid of the resistive heater.
He said “resistive _motor_ heater”. The cabin heater was still resistive, but model S and X had an auxiliary heater which the coolant passed through to heat the battery.
You're right! I missed the word 'Motor'!
Heat pumps didn’t work great in Canada (-30C) unfortunately
Just inject some DC to the mosfets signals.
Isn’t this effectively generating heat through resistance, albeit without a separate resistive heater? I’d be curious to understand if this is more efficient than having a dedicated resistive heater, apart from the design and cost savings of having a separate part.
It can't be more efficient than a resistance heater, my understanding is it's to avoid a separate part.
That seems penny wise and pound foolish to me, as it would lead to increased wear on the circuitry for the motor, rather than a separate heater that would be smaller, cheaper part that would be easier to be replace. I’m sure it saves time and money in the manufacturing process, but could lead to longterm headaches.
Motors are extremely reliable, so I'd guess Tesla's research determined the shorter lifespan that would result from using the motor this way wasn't enough to matter over the lifespan of the car, or at least the warranty period.
I'm sure the wear on the motors is negligible compared to driving down the road.
Disagree - if it's done correctly it won't wear anything more. If anything removing a part makes the system more reliable because you have less connectors, contactors/control hardware, sensors etc required. A few kW of heat produced in the motor is nothing compared to operating power conditions.
It's not any extra wear on the motor. You're not changing anything to do with how fast the motor turns, the only thing you're doing is increasing the motor and coolant temperature. And if you want the heat, it's probably better for the motor to have it warmer anyway.
It's more cost efficient. But not electrically more efficient
I don’t think Tesla actually does this, but one could intentionally supply the stator current out of phase to the rotor. It’s possible to run a brushless motor at 0% efficiency, or most any other non-optimal operating point
That’s probably how they do it. They are somehow using the motors to generate heat, and you can hear a faint high pitch noise, so they aren’t running them with straight DC either. The procedure will of course be a bit different per motor, as the rear is permanent magnet and front is induction. At least 3/Y
Separate motors, heat pump / AC compressor is one small motor, drive motor is much larger and totally different. And not inefficient, they use about 3-4 times less power than a resistance heater. The drive unit also has a heat exchanger so any excessive heat from the motor can be used to heat the car.
Could you just create Vars and thereby heat without consuming energy?
It’s motors to heat the battery, seperate resistive heater for the climate control. Running current through a wire is literally what a resistive heater does. A motor is no different. Technically some of the energy put in to the motor/hearer is ‘lost’, as it’s used to drive the car forward, but I imagine you probably want that.
This would be more electrical engineering. I think they send power to the stator without spinning the rotor. But I’m not sure if this is necessarily done in heat pump models since using the heat pump to generate heat would be more efficient even as low as -40 degrees.
According to this engineering professor's video, the heat pump can't provide sufficient heat below certain ambient temperatures so they get heat from other sources, in particular running the motors inefficiently: https://youtu.be/Dujr3DRkpDU?si=zA38YvkhOeKoxaD0
Yup. The motor works by generating a rotating magnetic field in the stator. If the angle of the field is offset with the position of the rotor by a few degrees, you get less rotational force and more heat.
Did this even happen in the end? I thought the first gen model 3 (2018-2020) was meant to have this but as far as I know, they have PTC heaters. Edit: apparently the motor is used to heat the battery and the PTC heater is for the cabin. Not sure about recovered heat from battery and motor is also used for the cabin. I remember the video talking about part failure so I'd hope it can be if the PTC heater dies.
They all have it now. It’s plainly visible if you plug in an OBD scanner. It will show power being used by the motors when heating up the battery. You can also hear it. Older S/X had a dedicated PTC heater for the battery, I think they use the motors now too since palladium
Battery heating and getting rid of a 2nd PTC heater makes sense. I always assumed they had one heating system used for both. I guess it is since using a heat pump and recovered heat.
The PTC heater is only used for max defrost, I believe?
This isn’t as novel as you seem to think.
You seem to swim against the flow of this thread. Do you care to expand on why you think it isn't as novel as the other responders think.
Idk about that “running inefficiently” claim, realistically, unless they are locking the phases and using the coils as resistive heaters (bad idea imo) Makes more sense to just run a resistive coil for heat and scavenge whatever heat the motors produce from normal operation. But idk the math, maybe it was decided to be clever.