[castratikron]

Question is whether those devices would be better off using brushless DC or some other DC motor? Tesla uses a switched reluctance motor (basically stepper motor) instead of induction motor on their low end vehicles for example.

[WorldMaker]

Just about every electric vehicle at this point uses DC induction motors. Many support AC fast charging with various sorts of battery hacks, but Lithium Ion batteries are kind of inherently DC when it comes to applying power to the motors. At this point DC motors generally seem to out-class their AC counterparts other than the efficiency of using the same current as walled outlets in homes.

The article puts it this way in a bullet point toward the top:

> DC motors and appliances have higher efficiency and power to size characteristics.

[elihu]

Actually, induction motors seem to be losing popularity in EVs, being replaced by permanent magnet motors which are more efficient (which also makes them easier to cool). And they're usually regarded as AC motors because they're fed 3-phase AC power from a motor controller (also called an inverter). The entire motor controller / motor system runs on DC power, so sometimes it's referred to as a brushless DC motor.

Fast charging is done with DC. Level 1 and level 2 charging uses 110 or 220 volt AC and is quite slow by modern standards.

[dreamcompiler]

All charging is done with DC internally. Level 1 and 2 charging uses a rectifier inside the car to convert AC to DC. Fast charging simply bypasses the rectifier.

The reason Level 2 charging is current-limited by your car -- even if you had a very high-current AC source available -- is that to take advantage of a high-current AC source your car would have to carry around a bigger, heavier rectifier. Which would decrease your EV's efficiency just by virtue of being big and heavy.

[elihu]

Yep, that's all true. I meant that L1 and L2 use an external AC power source.

[klondike_]

"Brushless DC" motors are actually 3 phase AC synchronous motors with an integrated DC-> AC converter. In industrial settings with 3 phase grid power they are very efficient

[dreamcompiler]

Not necessarily. Brushless DC motors are not required to be 3-phase or even to use sinusoidal waveforms. Most small BDC hobby motors (such as those on drones) are not even remotely sinusoidal.

[xxpor]

> AC fast charging

I believe you meant DC fast charging, unless you were referring to level 2 charging.

[WorldMaker]

Yes, I was referring to Level 2+ charging. Some EVs can charge surprisingly efficiently that way through some interesting engineering hacks, but yes overall the industry has moved on to DC fast charging standards with "AC fast charging" a fallback.

[kevin_thibedeau]

No. AC motors are more reliable simply by having fewer parts that can fail.

[jbay808]

The trend is towards DC motors that are electromechanically AC motors, but supplied with AC current generated by an inverter from a DC power source. The inverter can control the motor more precisely than a fixed-frequency grid voltage can, and the DC source can be supplied by a battery.

In terms of reliability, the inverter is still an extra part that can fail, but on the other hand, it's also much less likely to blow a fuse when your motor shaft stalls on startup.

[watermelon0]

I thought newer devices (washing machines, ACs, etc.) mostly used brushless DC / ECM motors, since they are more efficient and quieter?

They do need controllers that use AC, so I don't think that existing devices would work on DC.

[candiodari]

Yes but they work on feedback (if the washing machine has 5kg load, use frequency X, voltage Y, if machine has 10kg load ... they don't measure the load they measure how the motor reacts to their first guess voltage (this is called startup) and then adjust). Even comes with mechanical advantages: instead of using brakes, you just use the same motor and reverse the feedback.

Now if you want the ability to adjust frequency and voltage, at large power levels, you're talking about changing the parameters of an inverter. So what it's going to do with AC input voltage is AC -> DC -> AC* (* with different frequency and voltage, synchronized to the rotation angle changes of the drum of your washing machine). This comes with a second advantage: it's easier (and cheaper) to be tolerant to frequency and voltage changes in the wall plug, maybe even tolerant enough to have one device that works in US and EU (and ...)

You're doing this because the power plant is not going to change frequency or voltage based on how fast your washing machine is turning, but doing that makes the washing machine much more efficient.