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PMAC vs induction motor for model 3
- Thread starter No2DinosaurFuel
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PMAC is blasphemy. 9 years of Sunday School is hard to overcome.
The vibe I got at the M3 delivery event was that engineering is excited about the new motor(s). There are probably some who feel like "why change?" but the sense I got was that this is viewed as significant progress.
I am not sure by what metrics, but I would assume at least efficiency and reliability improvements. Costs I am not so sure, but efficiency improvements means less battery needed then it is helpful.
I am not sure by what metrics, but I would assume at least efficiency and reliability improvements. Costs I am not so sure, but efficiency improvements means less battery needed then it is helpful.
Rashomon
Member
It's a PMAC motor. The technology is very similar to that of Emrax, which claims to be getting even more power per kilogram than Siemens. Everyone working on aircraft motors that I know of is using PM -- unless they're doing research on superconductor-based motors running at cryogenic temps . . . maybe for mid-century airliners.
Supposedly F1 motors have even better power to weight by a factor of 2, but getting data on any of the current ones is almost impossible. Honda published data on their KERs motor from several years ago after they left F1. It made 60kW from 7kg. It was geared permanently to the engine, was freakishly efficient (98-99 percent) and used extremely high coercivity magnets and cobalt-based stator materials. That high efficiency means the Honda motor could run high power nearly continuously, aided by an oil cooling system. One motor designer I know described it as a $50,000 motor -- which is relatively cheap by F1 standards.
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Yes, 76 kg is the weight of the full Bolt EV drive unit which includes the motor, reduction gearing, and FWD differential.plus 7 liters of transmission fluid.
I wasn't clear on which variant of Model S that rear drive unit was from. If it was from a regular RWD S then the motor is rated for 285 kW, I think.
It's not clear if it's a performance version or not. According to wk057, the only difference between them is firmware - and even before that we thought it was only the inverter, so I'm taking that weight as being for the P85 complete drive unit or the complete S85 unit.
Several commenters have mentioned, in 13 pages of comments, why is a Permanent Magnet Motor more efficient?
There has also been much hogwash here and on InsideEvs regarding PM motors being 'partially induction' or some other tripe.
A PM motor has NO ELECTRICAL CIRCUITS in the rotor, so it can't induce anything and therefore is in no way, shape or form an 'induction motor', while an induction motor has electrical circuits. Wound-Rotor induction motors bring the currents out on external wires and may be measured with an amprobe.
To answer the basic question: A PM motor is more efficient since it has ZERO ohmic losses in the rotor since it has no ohmic currents. Going further - even if you PUT wiring in a PM rotor there would be of absolutely no use for it since the juice on the wires would always be off. Think about precisely why that would be...... (HINT: Its exactly the same reason why you don't get electricuted from a spool of wire hanging from the store shelf).
A PM motor has no electricity in the rotor to begin with. THE PM equipped '3' should do better on the race track, since there are no ohomic rotor heating losses to dissipate.
There has also been much hogwash here and on InsideEvs regarding PM motors being 'partially induction' or some other tripe.
A PM motor has NO ELECTRICAL CIRCUITS in the rotor, so it can't induce anything and therefore is in no way, shape or form an 'induction motor', while an induction motor has electrical circuits. Wound-Rotor induction motors bring the currents out on external wires and may be measured with an amprobe.
To answer the basic question: A PM motor is more efficient since it has ZERO ohmic losses in the rotor since it has no ohmic currents. Going further - even if you PUT wiring in a PM rotor there would be of absolutely no use for it since the juice on the wires would always be off. Think about precisely why that would be...... (HINT: Its exactly the same reason why you don't get electricuted from a spool of wire hanging from the store shelf).
A PM motor has no electricity in the rotor to begin with. THE PM equipped '3' should do better on the race track, since there are no ohomic rotor heating losses to dissipate.
Not sure what to make of it, but according to the Car And Driver: "The Model 3, like the Model S, is a rear-wheel-drive car in its base form, with a rear-mounted AC induction motor"
JeffK
Well-Known Member
They likely just made an assumption.
The older article Charged EVs | Tesla’s chief motor engineer discusses the potential of next-generation motor technologies
pretty much gives away that they are using magnets.
I would not dismiss Car and Driver's statement so easily.
Note that EPA document has other information that is questionable, for example battery specific energy at inexplicably high 150Wh/kg. So it is possible that EPA document, rather than Car and Driver is wrong.
As far as I am concerned, the jury is out on this.
JeffK
Well-Known Member
I am just looking at the evidence...
- The EPA doc
- The rumor from the Chinese magnet company last year. Note this was an official press release from that company unless you think they were lying, which is possible who knows.
- Then the Chief motor designer at Tesla answering a question about motor costs speaks immediately about magnets without being prompted.
The evidence against is the car and driver article and Tesla's past use of induction motors.
Thanks for the link. Here is how I would speculatively explain it:
- Car and Driver was at the handover.
- They asked some questions, and got answers, for example: "The Model 3 doesn’t use the same battery technology as the Model S. It uses cells with a new chemistry and format produced by supplier Panasonic."
- They did not ask other questions, as the EPA report was not widely circulated. Where they did not ask questions they presumed "same as Model S" as anyone would.
For example, I thought they were going to save the permanent magnet motor for the front motor and use induction for the rear, just based on schedule. Was the EPA report for the two, or all, wheel drive version?
SageBrush
REJECT Fascism
He was attending a conference on motors. I would not expect him to focus on Tesla unless asked.
JeffK
Well-Known Member
True
there's also this:
New Tesla Model 3 details revealed by EPA: ~80 kWh battery pack, 258 hp, and more
Where there were updates and corrections from Tesla, but no corrections regarding the type of motor.
I think we are giving to much credence to the data in EPA report that are not coming from testing.
Once again, 150Wh/kg is lower energy density than Model S. This specific energy from the EPA report is almost definitely wrong: I do not see how Model 3 weight could be reduced by 20% as compared with the Model S if battery weighs **more** and bodywork incorporates aluminum **and** steel.
So again, I am not saying there is certainty here, but there are other data in EPA report which are most likely wrong.
Once again, 150Wh/kg is lower energy density than Model S. This specific energy from the EPA report is almost definitely wrong: I do not see how Model 3 weight could be reduced by 20% as compared with the Model S if battery weighs **more** and bodywork incorporates aluminum **and** steel.
So again, I am not saying there is certainty here, but there are other data in EPA report which are most likely wrong.
Zaphod
Galaxy President (former)
Interesting, makes it sounds like in the dual motor version there will be one of each type, one PMAC and one AC induction. Plot thickens...
SageBrush
REJECT Fascism
I didn't read it that way at all, just that the motor firmware for AWD is more complicated.Interesting, makes it sounds like in the dual motor version there will be one of each type, one PMAC and one AC induction. Plot thickens...
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