How Does an Electric Motor Work?
Some time ago, we talked about transformers and transformers that hum. That was a pretty interesting concept. Electricity can make things move thanks to electromagnetism. When you put energy into something in just the right way, it produces a magnetic field. We can probably all remember messing with magnets in our youth, watching how no matter what, we couldn’t make two magnets touch each other or how we struggled to separate them (depending on the poles involved). That’s basically what makes your electrical motors, your fans, compressors, and everything else tick.
Let’s take a deeper look.
Simplest, Working Motor
We’re going to start somewhere simple. As simple as we can. Two magnets, a power source, and a single electrical winding.
Simple Enough, Right?
On the outside, we have two magnets. We have a north pole and a south pole. We’re giving our north pole a positive polarity and our south pole a negative polarity. Then we have a power source, connected to a copper winding with those two semi-circular pieces of metal, called Commutators. This inner winding of copper is called the Rotor. It too, has polarity. It’s polarity is exactly opposite to the magnet. No matter how the copper winding moves, it’ll always be opposite. This causes it to just about always be attracted to the nearest magnet.
The attraction is such that the rotor wants to reach where the magnets end. This causes it to want to be diagonal. Of course, by the time it’s reached that point, it has momentum. It’ll spin passed, and the winding will receive the opposite charge as our power source is reversed.
This is the most basic electrical motor you can make. It won’t have an even delivery of power and it’ll probably be pretty tiny. It’s really expensive to make gigantic magnets. Luckily, we don’t need magnets to create electromagnetism. We can just create an outter winding.
Let’s add field windings. These are huge, copper windings that will generate an electromagnetic field that opposes our rotor’s field. This allows us to make the motor as big as we like, as copper is easy to acquire and the field will be whatever we wire it to be. This gives us arbitrary size and performance based on our needs.
You can see this is just one gigantic mess of copper.
We still have another flaw though. That power delivery isn’t even. When the rotor is vertically oriented, it really doesn’t want to move much. It may even be enticed to slow down. We need to smooth out the delivery of power. To do this, we add even more windings. More windings mean that there will always be a part, or parts, operating at peak attraction to the field winding.
Now we’re getting to something like a modern electrical motor. The rotor has many, many windings, allowing for optimal, near constant delivery of power. We’ve separated these windings with specialized metal plates to hold them in place under heavy loads and prevent the windings themselves from moving and shorting out. We just have one last concern to worry about. The greatest nemesis of all motors.
We’re going to be pumping electricity into this thing. A lot of electricity to be frank. Even in copper, with it’s low resistance, lot’s of power means lots of waste heat. The longer this runs and the more load we put it under, the hotter it’s going to get. This is going to be a problem. Without some kind of cooling system, whether it’s a massive heat sink, a liquid cooler, or amazing ventilation, the motor’s going to melt and short out.
In many cases, the very nature of the rotor already solves this problem. The rotor spins. Fans spin. If we put a fan blade on the rotor, it’ll suck air into the motor housing and cool the entire thing. This is only helped by copper’s massive thermal conductivity. If we cool one part of the copper, it will help to cool the rest. In a way, the entire motor is almost a heat sink.
We added a fan to keep it cool, a case to keep it safe and satisfy OSHA that we’re not gonna have a whirring machine of death running out and around, causing trouble.
The Wrap Up
What did you think? Did we get something wrong? Got something for us to cover next time? Let us know in the comments below.