How do different electric motors work and what’s the difference? What type does Tesla use?
In: Engineering
This question would probably be best-asked on /r/teslamotors. The community can be very helpful.
I, personally, don’t know a whole lot on the topic except to say that Tesla, among other motors, uses a permanent magnet motor, which works by being charged on/off in rapid succession, which in turn creates a rotating magnet field that causes a second part to be repeatedly pulled and, thus, turned.
I believe.
All (with some exotic exceptions) electric motors work roughly the same: You got (electro-)magnets attracting and repelling each other in an endless cycle, converting electricity into mechanical power.
The following is a very brief list of the most common types. I’m trying to keep it simple, but I can’t dumb it down arbitrarily 😉
**Permanent Magnet DC Electric Motor:**
This type of motor uses permanent magnets in the stator (the outer, non-spinny bit) and electromagnets in the rotor (the spinny bit that’s coupled to the shaft). Carbon brushes and a commutator (spinny copper strips that the brushes wear on) transfer electricity to the rotor and also switch (commutate) between the different electromagnets as they spin insinde the stator’s magnetic field.
PM DC motors are most commonly used in low power applications such as toys, cordless drills and older/cheaper RC models. They are quite efficient but produce a fair bit of electrical noise and the brushes will eventually wear out.
**Electrically Excited DC Motor/Universal Motor:**
Same as the above, but using electromagnets for the stator field. Depending on how thea are designed, they can also run on AC, hence why those types are called Universal Motors.
This type of motor was used in earlier electric vehicles (EVs) because they are powerful, yet very versatile and easy to control across a wide range of torque and speed. Some electric locomotives still use them as traction motors and they are also very common in vacuum cleaners, car starter motors, leaf blowers etc. Efficiency isn’t as great since now you also have to power the stator.
**Brushless DC Motor (BLDC):**
Thanks to the continued miniatiuization of power electronics, this type has gained a lot of traction (heh). Instead of a a rotating electromagnet, BLDCs spin the permanent magnets while the electromagnet is stationary. This way, you don’t have to send power to the rotor and, except for the bearings, there are no moving parts. Commutation (switching between electromagnets) happens through transistorized electronics which also allows very precise control speed and torque.
BLDCs have been around for quite a long time in computer fans and stepper motors (e.g. in printers), but more powerful versions really only came to market in recent years. Due to their excellent efficiency and reliability, BLDCs continue to replace more and more other motors. Fancy electric drills, air conditioners, fridges, RC planes and some EVs have already made the switch. The only downsides are cost for the powerful rare-earth magnets and the electronics module.
**Induction Motor/Squirrel Cage Motor/Asynchronous Motor:**
Induction motors have a rotor made of aluminium, sometimes with copper bars to make it more electrically conductive. When AC power is sent to the stator coils, the alternating magnetic field induces a current in the rotor, which in turn creates a magnetic field of its own. This results in torque and the rotor starts spinning.
Because the rotor relies on a changing magnetic field to keep itself powered (and hence “magnetized”), it will always run a bit slower than the AC frequency may suggest. A 50Hz supply will produce a field that is “spinning” at 50Hz*60s=3000RPM (or a fraction thereof), but the rotor will rotate more slowly, say at 2700RPM. The difference is called “slip” and depends mainly on how much torque the motor is outputting. Ask for too much torque and the rotor will fall behind too much and the motor quickly stalls out.
Due to their cheap, simple design, their exceptional reliability and good efficiency, induction motors are very common whereever there is an AC supply. Applications include fans, air conditioners to large industrial machines and many more. Variable frequency drives (VFDs) similar to those used with BLDCs allow for speed control and can also supply the induction motor from a DC source, opening even more applications such as in tractoon motors for EVs and electric locomotives.
**Synchronous AC Motor:**
Synchronous motors come in many different flavors, so I’ll be glossing over a lot of details here. For more insight, I recommend you check out the wikipedia article.
Synchronous motors can be made similar to induction motors but with a rotor made of steel rather than aluminium. The rotor will then “snap” to the stator’s spinning magnetic field and run in sync with the AC frequency. This can be useful for applications where the exact speed matters, such as mains driven mechanical clocks or old cinema projectors.
Another type uses a spinning electromagnet that is energized through brushes and sliprings. Combined with a VFD, this variant offers excellent speed and positioning control, useful for powerful servo motors for e.g. CNC lathes and also very high efficiency at low speeds which is crucial for large industrial ball mills. They can also be used as generators, for large scale power factor correction, as motor-generators in pumped-storage hydroelectricity and many other applications.
Just like with induction motors, synchronous motors will suddenly “snap” out of their rythm and stall out when over-torqued.
**tl;dr:** There are a million different types and subtypes of electric motors. Wikipedia should keep you entertained for a few days…
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