Tesla motor as a generator

eojjho said:

It was suggesteed that it might be an induction motor. 60 years ago I recollect doing an experiment that getting an induction motor genetating required parallel capacitance, and drawing curves speed / volage with variable capacitance. So IF an induction motor, the Tesla controller must incorporate circuitry to manage regen.

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Yes, the original Model S and Model X small and large drive units have induction motors, and the controllers are completely capable of operating them as generators (and they do so with every brake application).

catphish said:

Was that specified? I'm mostly only familiar with Model S motors, which are squirrel cage induction motors. I think one should be able to get decent efficiency with either type though.

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No, the motor type was not specified, but with no useful response from the original poster the working assumption is that the early induction drive units are the subject of the discussion. Yes, these are "squirrel cage" induction motors, with aluminum conductor bars.

The Model 3 and Model Y front drive units also have induction motors, but the rotor has copper conductors in the Model 3 (see 8:56 into the WeberAuto video "Tesla Model 3 and Y Modular Motors" in YouTube). With new drive units now at both ends of the Model S (and presumably Model X), they may be using induction for the front drive units again, but I do not know (when the new generation motors were first used in the Model S they used a PM motor at the front and the old induction motor at the rear).

I agree that efficiency in the vicinity of the optimal operating point will not be much different between the induction and PM motors.

piotrsko said:

Regen is just a freebie to inefficiently add some energy back into the pack instead of making brake heat and nowhere near what a dedicated generator will do. If you want to build a tesla powered turbine, go ahead just don't expect much output or efficiency. I have popcorn and maybe ten years life expectancy left, post when it's done.

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I doubt that efficiency at the optimal operating point is a problem. Of course, that operating point is at a much higher power than this homebrew wind turbine is likely to achieve. My guess is that the operating efficiency advantage of PM over induction in EVs is likely at points away from the optimal.

Induction machines are commonly used in commercial-scale wind turbine generator sets; however, due to issues with control (more than with efficiency) they are usually not the simple "squirrel cage" type.

catphish said:

What makes you think a Tesla induction motor would be inefficient as a generator? What difference is there in the construction of a "dedicated generator"?

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A dedicated generator may be a synchronous machine (rather than asynchronous or "induction"), with either a wound rotor (typically powered via slip rings) or permanent magnets. These types of machine are all used as motors in EVs.
When a large wind turbine's generator is an induction machine (which is very common, especially in older units), it commonly has a controlled rotor winding (in which current is still induced by slip versus the stator field) to better manage the generator. I've never heard of an EV using a motor with a controlled induction rotor; the Tesla motors are simple squirrel cages.

JoeInOz said:

I'm not attacking you, btw, just suggesting you question your curren knowledge a bit more thoroughly - or not reply to posts you don't understand...

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I'm questioning your knowledge of Tesla motors. It's understandable that someone new to the field (EVs) doesn't know much yet, but perhaps you should take your own advice.

catphish said:

... I believe the largest generators use slip rings, but I don't know if that's for efficiency or just control, hence my question.

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I believe that large generators, such as in hydroelectric plants, are normally synchronous wound-rotor machines (with rotor excitation via slip rings), for control, for efficiency, and because large PM rotors were not practical until recently.

Large (thousands of kilowatts) industrial motors can also be synchronous wound-rotor machines, but are routinely induction motors; they are at least as efficient as the PM motors in EVs, but they generally operate only at a fixed speed and in a narrow torque range, and there are advantages to large scale.

JoeInOz said:

Even my 1978 Honda CX500 had permanent magnets in the generator rotor....

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Fascinating. The CX500 apparently had a 6-pole three-phase outer-rotor PM generator. I don't know if this is now standard practice in motorcycles, but I have noticed similar stators for other bikes. PM automotive generators are rare; in light-duty vehicles they are still generally three-phase inner-rotor wound rotor machines with simple diode output rectification and control by regulation of the rotor excitation (which is connected via slip rings). Heavy vehicles with no-slip-ring alternators typically use induction coils to transfer excitation to a wound rotor... they're still not PM.