PMAC vs induction motor for model 3

[22522]

Model 3 apparently has no battery heater but use the inverter and motor even when standing still:


Tesla Model 3: Exclusive first look at Tesla’s new battery pack architecture

Is this possible on both PMAC and Induction motors?

Good questions. Good article. I think the idea here is to use a concentrated heating element and distribute the heat using liquid pumped through the batteries.

I do not currently have the dexterity on motors to answer the question. But from a heat transfer and current draw perspective a resistive element thermally coupled to the motor case could provide concentrated heat source with a good thermal path to the batteries in either case.

An electric water heater element in the a flow path would work and be very inexpensive. But that is not what the article said.

Hope we get an answer.

(I'll figure it out next week if we don't get one by then... Pretty sure if you run DC through the winding in a controlled way, no spinning will happen. So either will work.)

 

[KarenRei]

It's not a "heater element". They're running the motor at 0% efficiency, so it only yields heat, not torque - basically as a resistive heater. The motor is glycol cooled, and its loop can be connected or disconnected from the cabin and battery loops by actuated valves (at least if it's set up the same way that the S and X are) (the battery loop is isolated by a heat exchanger so there's no actual exchange of coolant). The motor in such a case should also be providing cabin heating, eliminating that heater as well. We're talking some serious simplification.

Tesla always comes up with the most off-the-wall clever solutions for things.

 

[MP3Mike]

the battery loop is isolated by a heat exchanger so there's no actual exchange of coolant

I don't think that is true with the Model S/X, are you saying that they changed that with the Model 3?

 

[KarenRei]

I don't think that is true with the Model S/X, are you saying that they changed that with the Model 3?

According to the Tesla patent diagram it's that way.

Then again, a patent doesn't mean that that's actually how they implemented it.

 

[KarenRei]

Ed: Found a different patent from them where they show valves that can connect or isolate the battery loop, rather than using a heat exchanger; in this version, they only show the heat exchanger used with the HVAC system (which they have to, since it contains refrigerant rather than glycol):

 

[Swampgator]

Karen,my link was broken but the article was describing the function and efficiency of a PM assisted reluctance motor.
I think this may be what Tesla is using for Model 3. Possible?

 

[KarenRei]

Karen,my link was broken but the article was describing the function and efficiency of a PM assisted reluctance motor.
I think this may be what Tesla is using for Model 3. Possible?

Here's what Tesla's chief engineer had to say about reluctance motors back in April:

Charged: There is a lot of talk about switched reluctance machines (SRMs) as a possible next-generation EV traction motor. Do you have any thoughts on SRMs?

KL: An SRM is a very particular machine. It’s very simple to manufacture, but it’s difficult to control. It’s got some acoustic noise and vibration challenges. With design you can make it a lot better, and you can control it in a way that you mitigate all these problems.

It is not too bad in torque density, but the constant power is a bit of a challenge to build up, and you need constant power in traction applications. So, again, I’m always hoping to see new ideas and definitely it’s attractive to have something that is so robust because it’s a very simple rotor construction. It could potentially work for this class of problems.

 

[Swampgator]

I found the pdf

 

[SageBrush]

The motor in such a case should also be providing cabin heating, eliminating that heater as well. We're talking some serious simplification.

Presuming 15 kW output on the highway and 3% inefficiency (is that too much ?), we are talking 450 watts of heat.
Is that enough for cabin heating ? Or perhaps the battery will be additive.

It would just be amazing if the car's inefficiencies could warm the cabin on long drives.

 

[KarenRei]

Presuming 15 kW output on the highway and 3% inefficiency (is that too much ?), we are talking 450 watts of heat.
Is that enough for cabin heating ? Or perhaps the battery will be additive.

It would just be amazing if the car's inefficiencies could warm the cabin on long drives.

3% inefficiency? No, no, no - when heat is needed, they run the motor as inefficiently as they can (at as high of a power as they can take the heat away). It's a weird concept, deliberately running a motor inefficiently, but it's a neat solution to simplifying heating.

 

[SageBrush]

3% inefficiency? No, no, no - when heat is needed, they run the motor as inefficiently as they can (at as high of a power as they can take the heat away). It's a weird concept, deliberately running a motor inefficiently, but it's a neat solution to simplifying heating.

Yes, I understand that one use is pre-heating. I'm thinking of afterwards during a long trip

 

[Rashomon]

Speculation from Otmar, (inventor of the Zilla controller)

I like the Otmar video. He's talking about high-saliency Interior PM (IPM) motors. See: Understanding permanent magnet motors | Control Engineering

BMW uses this design on the i3, and my understanding is you can get about a 20 percent torque benefit in the same package size from a well done execution compared to a SPM motor. Someone who knew a lot more about this than me once told me a lot of these concepts were originated by a Canadian EE professor (whose name I forget) many years ago, who ended up being retained as a consultant for Toyota for the Prius drivetrain.

 

[Saghost]

Yes, I understand that one use is pre-heating. I'm thinking of afterwards during a long trip

If they can artificially generate 5 or 10 kW of heat from deliberate inefficiency with no torque, I don't see any reason they couldn't superimpose the two, and generate both the small torque needed to drive down the road and the waste heat from a much higher current flow.

 

[Saghost]

Ed: Found a different patent from them where they show valves that can connect or isolate the battery loop, rather than using a heat exchanger; in this version, they only show the heat exchanger used with the HVAC system (which they have to, since it contains refrigerant rather than glycol):

The model S system seems to be much more like this one than the prior patent. Here's the beautiful diagnostic screen full of useful information that they lock away behind technician login credentials so I can't have it:

Taken from here.

 

[SageBrush]

If they can artificially generate 5 or 10 kW of heat from deliberate inefficiency with no torque, I don't see any reason they couldn't superimpose the two, and generate both the small torque needed to drive down the road and the waste heat from a much higher current flow.

I don't see why two modes have to be superimposed. Just collect the heat and route it to the cabin when it is not needed somewhere else.

 

[Saghost]

I don't see why two modes have to be superimposed. Just collect the heat and route it to the cabin when it is not needed somewhere else.

Maybe I misunderstood. I thought your post a couple above the one I quoted was asking whether the heat generated from inherent inefficiency was going to be sufficient to warm the battery or keep it warm during normal operation while driving along the road in cold weather. The point I was making is that if it is not, they can presumably use the same "0 torque" technique they used when parked mixed together with the normal operation to generate additional heat while driving if need.

 

[SageBrush]

Maybe I misunderstood. I thought your post a couple above the one I quoted was asking whether the heat generated from inherent inefficiency was going to be sufficient to warm the battery or keep it warm during normal operation while driving along the road in cold weather. The point I was making is that if it is not, they can presumably use the same "0 torque" technique they used when parked mixed together with the normal operation to generate additional heat while driving if need.

I was thinking (hoping ?) that after the battery is warm then normal operation results in excess heat that can be routed to wherever it is desired.

 

[gregincal]

I was thinking (hoping ?) that after the battery is warm then normal operation results in excess heat that can be routed to wherever it is desired.

Not in really cold temperatures. There just isn't enough heat generated naturally. The whole point of EVs is that they are really efficient, which means they don't generate much waste heat.

 

[SageBrush]

Not in really cold temperatures. There just isn't enough heat generated naturally. The whole point of EVs is that they are really efficient, which means they don't generate much waste heat.

Perhaps I am way off, I'm under the impression that battery to wheel has ~ 7.5% losses

 

[JRP3]

Let's say it takes about 20kW for steady state cruising around 65mph, with a 90% efficient motor/inverter that leaves about 2kW of waste heat. I'd expect at least twice that needed to keep a vehicle warm in 30F air temps.