When you read articles and reviews about electric chainsaws you may occasionally come across the terms ‘brushless’ and ‘brushed’ motors. In this article I will go into a little more detail about these motors and let you know what the advantages and disadvantages of both types are and whether you need a brushless chainsaw.
How electric motors work
Both types of motor work in the same way. They have permanent fixed magnets on the outside which don’t move. On the inside there is an armature which rotates (and is therefore also called the rotor) and this also contains an electromagnet. When the windings (copper coil) in the motor become energized a temporary magnetic field is created which repels and/or attracts against the permanent magnets. This force rotates the shaft allowing the motor to function. The armature will turn continuously as electric current is routed through different sets of windings, maintaining the repulsion/attraction.
Next let’s look at the workings of each type.
As mentioned above, electric current is routed through different sets of windings to keep the armature turning, in effect continually changing the poles of the electromagnet. The brushes deal with this change in polarity by making contact with two spinning electrodes attached to the armature.
In simple terms it is these brushes which deliver current from the battery into a commutator which then passes the charge to the motor windings (on the armature). This magnetizes the windings, which are pushed against a stationary rings of magnets surrounding it, making the armature spin. This spinning continues until the charge from the battery stops.
The advantages of brushed motors include:
- Simple set up. Can be wired direct to DC power
- Cheap to manufacture
The disadvantages of brushed motors:
- The brushes will wear out as they are in constant contact with the shaft.
- They produce lots of electromagnetic noise. This is because the brushes are continually making and breaking connections.
- The speed of the motor is limited by the brushes.
- The motor is harder to cool because of the electromagnetic is positioned in the center.
These motors have a more complex design. As the name implies there are no brushes but in addition to this the commutator is also lost. The positions of the windings and the magnets are also reversed so that the copper windings are not on the armature but are fixed and surround the shaft. Energy is channeled to the copper windings not by brushes and commutator, but by a small circuit board.
The advantages of brushless motors are:
- Less electrical noise as there is no sparking
- No brushes to wear out
- Very easy to cool
- Greater efficiency as the motor is controlled by a computer and not mechanical brushes.
The disadvantages of brushless motors are:
- Higher initial cost.
So how does this relate to chainsaws?
If all other factors are equal (such as battery size in cordless saws), then you should get better performance from a saw with a brushless motor.
It is estimated that these are typically 85%-90% efficient whereas brushed are around 75-80% efficient. This is because the tool will adjust depending on the task being carried out. So, for example, if you are cutting through a two inch thick softwood limb the tool will adjust for the resistance and pull only the charge it needs from the battery. If next you try to cut through five inch diameter oak the tool will adjust and draw more current from the battery. This ‘smart readjustment’ will in turn provide greater battery runtime.
The other advantage is that a chainsaw brushless motor, as well as being more durable, is likely to last longer than an equivalent brushed version. The downside is that the saw is likely to cost more, although the cost will be recouped over time thanks to the increased efficiency.
Do I definitely need a brushless motor?
Given their obvious advantages you might think that these are a must when it comes to buying a new chainsaw. So do you definitely need one? The answer is not necessarily. There are plenty of excellent chainsaws which have traditional brushed motors and as with many buying decisions it is often a matter of considering the benefits versus cost. As mentioned earlier, you are likely to pay more for a brushless model.
That said, they do provide a number of advantages and if you are prepared to spend that little bit extra they are worth considering. If you are interested in buying a brushless chainsaw, the models listed below are examples of products currently available on the market.
Click on any of the above links to read the full reviews.