With regard to power tools. I’ve Googled and read, and it only seems to confuse me more. Thank you.
In: Engineering
Electric motors have several electromagnets that need to be turned on and off at the right time to get it to spin.
In a brushed motor this switching on and off is done mechanically by a set of brushes riding on a spinning ‘commutator’. Picture a really tiny Wheel of Fortune with electrical contacts (brushes) instead of a flapper. Which magnet is turned on depends on which segment of the Wheel of Fortune is currently touching the brushes.
In a brushless motor this switching is done electronically using transistors instead of mechanical contacts. This has a number of advantages: Since there are no brushes, they don’t wear out, don’t make noise, you can use higher currents and you also have more control over the timing of when you turn a certain electromagnet on or off.
This is why brushless motors can be more powerful, quieter and they don’t have problems with brushes wearing out.
The gist of it is that there’s a couple ways to get rotation from an electric circuit. One involves a constant current (DC), but needs “brushes” to swipe along your spinning electromagnet, in order to keep your current flowing.
In a brushless motor, you actually vary your current with 3 phase AC (alternating current), and that lets you rotate your motor without those brushes. This can give you longer tool-life, as those brushes get a lot of wear.
(You’ll see brushless motors called brushless DC, even though they run on AC. This is because you can run the entire assembly off of DC as it is turned into that 3 phase AC by a component of the motor)
So imagine the rotor (the central portion of the motor) thats rotating inside the stator (the outer casing). There is power that needs to be given to the rotor in the form of electricity. This electricity runs through some copper coils and creates a magnetic flux (at multiple circumferential locations or coils placed around the rotor) . The magnetic flux created in the rotor interacts (attracts / repels) with the corresponding magnetic flux created by the permanant magnets mounted on the stator inside surface. This is how the rotor (hence the shaft) rotates.
Now remember – that power is being supplied to a rotating part. How to ensure that electricity wires are connected continuously to the rotating part? This is done by brushes (which are actually nothing like brushes but are rather solid blocks of low friction and low resistance material – normally some form of carbon or graphite). So the brushes are stationary – fixed – and the rotor is in constant contact with the brushes getting the power to create its magnetic flux (through specially designed terminals, called commutator, corresponding with each magnetic flux location)
Now there is a matter related to positive / line and negative / neutral of the electricity – but that discussion may need some images to explain.
Brushless motors on the other hand use electronics to keep shifting the power to different magnetic flux locations / coils on the rotor creating a rotating magnetic flux (not in the rotor but in the stator).
Hope that helps…
There are two parts to an electric motor: the stator and the rotor. The stator is the stationary part and the rotor is the part that rotates. Both the stator and the rotor have magnets, and the magnetic attraction or repulsion is what causes the rotor to turn.
In most motors, the magnets are electromagnets, which are coils of wire that are hooked up to the power. The problem is, how do you connect up wires to the electromagnet on the rotor. It needs to turn, and if you just connect the wires directly they’ll twist around the shaft until they break. You need a way to get the power to the coil but not have a direct connection.
This is where brushes come in. Brushes are typically a small block of carbon that slide along, or “brush” along, a strip of copper attached to the rotor. The strip of copper is called the commutator. The commutator is connected to the coils on the rotor. With this arrangement you can supply electrical power to the rotor coil, and it is free to rotate without tangling the wires.
The problem with brushes is that they introduce a small amount of friction. They will wear out over time and need to be replaced. Also, if the rotor has multiple coils (which almost all brushed motors do), the commutator will be divided into segments with each segment connecting to a separate coil. In between the segments there are gaps. When the brush bridges the gap, there is a spark. This can be dangerous around flammable gasses and is electrically noisy as well.
However, there is no need for the magnets on the rotor to be electromagnets. We can create fairly powerful permanent magnets. By using permanent magnets on the rotor, we eliminate the need for brushes and commutators, and the whole rotor can be made smaller.
The key to a brushless motor is that there needs to be a rotating magnetic field in the stator coils. This is done with a clever little electronic circuit that energizes the stator coils in sequence. As the magnetic field in the stator coils changes, the permanent magnets turn the rotor to maximize the magnetic attraction and minimize the magnetic repulsion.
Very informative! Thank you to all they replied!
But how do brushless motors use electronics to transfer power? I see a lot of similar answers, but nothing past that point.
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