Time to read: 6 min
尽管电动机驱动了截然不同的应用，但它们的核心功能保持不变，可以将电能转换为机械能。许多文章强调了市场上每个独特电动机的特征，但可以将它们简化为两个总体类别：交流电（交替的电流）电动机和DC（直流电流）电动机。
Each type has its own pros and cons, and this article is intended to give you a clear picture of how either an AC or DC motor can best suit your application. Let’s explore the ways in which they each convert electrical energy, the differences in their construction, and the best use cases for each type.
力量
The glaring difference between the two types of motors is the power off which they run.
交流电力,或交流电,voltage reverses every half cycle, which in turn changes the direction of the current. This is done by alternating the polarity at each end of a wire. So, if you take the U.S. standard of 120V/60Hz supply, there are approximately 120 half cycles per second.
使用直流电或直流电流，电流的流必须保持沿单个方向（正到负），因此电压必须保持恒定，以保持稳定的电流流动。您可以将直流电视为电池，具有明显的负端子和正终端。
AC Electricity for Motors
在使用交流电力的电线内，电子不会像DC那样沿单个方向行驶，它们只是来回摆动并传递能量（想想Newton’s Cradle).
Alternating current is used for power distribution systems (power to your home/office), for the simple reason that power transmission is much more efficient at higher voltages, and back in the day, AC transformers significantly advantaged DC voltage converters. However, advances in power electronics have made High Voltage Direct Current (HVDC) a new trend. Why are AC transformers preferred? Because the back-and-forth “wiggling” of electrons creates an electrical field, so a transformer can be used to kick up the voltage and in order to keep current relatively low.
And by keeping current low, resistance through the wire is reduced, which equates to a higher efficiency. This correlation between resistance and voltage can be found in the Power Law: Power = Current * (Resistance)^2.
So what does all of that have to do with an AC motor? Well, basically, AC motors are great for applications that require little precision, like a blender or your washing machine. They’re objects you need to start, and they may ramp up or down in speed, but the difference between 400 RPM and 420 RPM probably isn’t critical.
DC Electricity for Motors
DC motors, on the other hand, are all about precision and stability, because the DC power supplying these motors comes in at a constant voltage. The electrons inside the wire can only travel in a single direction, and they do so at a normally steady pace.
Again, this is similar to the way a triple A battery will constantly give your electronics a supply of 1.5V (excluding losses) until they die. This is better when you have delicate circuitry/circuit boards or electronics that need a steady supply of energy to function properly, like a laptop.
But wait—if my home is supplying AC power, but my product requires DC power, what do I do?! Most electronics will have an AC to DC converter. That’s what that block is on the power cord for your laptop.
实际上，您可以感谢缝纫机上的转换器，为乐队AC/DC的名称背后的灵感提供了灵感。使用直流电动机，您可以通过调节电压来控制速度，因为速度与施加到电枢的电压成正比。
建造
尽管AC和DC电动机的工作原理都是相同的（一个追逐另一个磁场的磁场），并且它们的外部可能没有明显不同，但内部存在一些基本差异，使它们每个人都独特。当您阅读以下信息时，请记住，差异是由它们的输入/输出驱动的：AC电动机以效率和功率为目标，交替电压，而DC电动机则保持恒定电压以保持稳定性。
AC Motor Build
AC motors are very simple because the alternating current does all the work. By injecting current through a stationary winding in the casing that surrounds the shaft, you’re creating a varying magnetic field, which induces a current on the shaft or rotor. This conversely generates a magnetic field that constantly tries to align with the magnetic field of the stationary winding, in turn causing the shaft to rotate.
Thus, their speed is associated with the amount of slip, or lag in their magnetic fields trying to catch up, which is defined by the motor’s construction.
Remember, AC electricity goes from “positive voltage” to 0 to “negative voltage” at double your frequency (Hz) every second. This means that with the U.S. standard of 60Hz, the current changes direction 120 times a second.
AC motors’ simplicity makes them long-lasting and significantly reduces the chances of mechanical error. However, their startup currents are typically around six to nine times the steady state current. The mix between efficiency and long shelf life makes them popular for applications where you don’t want too much energy loss and don’t want to be constantly replacing a motor (think washing machines). However, I depend on my washing machine enough that I’d probably pay every year to get a new one if it broke down—don’t tell LG!
直流电动机制造
因为汽车不可避免地需要一个旋转磁场ield, and DC current generates a constant magnetic field, their construction is a little more complex. Returning to the battery example we used earlier, we want the battery to supply a consistent 1.5V to our circuit board, instead of the craziness of switching from +1.5 to -1.5V hundreds of times a second that AC power gives us. In that same way way, in order for a DC motor to convert the consistent voltage supplied to it, we need a motor construction that will precisely convert that voltage into mechanical energy.
To do so, we need to first implement some mechanical functionality to create the rotating magnetic field that moves the motor. Again, this was easy with AC motors, because AC power naturally swings back and forth, which varies the magnetic field. With DC, the magnetic field will remain the same.
So, to counter, we have several rotating coils at the center of a DC motor, which connect to a “commutator.” The commutator makes contact with stationary “brushes” of opposite polarities at the exact moment that it needs to change the direction of current to rotate the shaft.
这可能是显而易见的，但是这里的主要缺点是由于换向器和刷子之间的接触引起的摩擦，因此效率的丧失。效率的损失以热量形式出现，如果您超负荷电动机，则有时会发生火花。
Function
如果您厌倦了阅读所有技术细节，并且真的只是关心最适合您需求的电动机，那么漫长的答案是，它归结为您的特定应用程序。作为一个简短的答案，这是每种电动机的利弊的基本列表：
Advantages of AC Motors
- 通常更有效
- 寿命更长，失败的机会更少
- 产生较少的热量
- Better for high power applications (washers, refrigerators, machinery)
- 无需转换器即可直接连接到家庭或办公室插座
交流电动机的缺点
- High startup current
- 有点笨重
- Not practical for portable applications
- Advantages of DC Motors
- Low electromagnetic interference (great for sensitive electronic devices)
- Stability for circuit boards and sensitive electronics
- 您可以在电池电源上运行产品
- 更好的速度控制
Disadvantages of DC Motors
- Typically more expensive
- Less efficient
- Higher chance of failure (Brushed type)
Main Takeaways
实际上，您的设计中可能会有几个因素可以推动您选择的电动机类型。如果您正在使用电路板，，，，batteries，，，，and require fine tuning on your speed controls, a DC motor is the way to go. If you’re going for high power, efficiency, long lasting, and can connect your product to a wall outlet, an AC motor will do the trick.
