Brushed vs Brushless

We’ve been hearing this term more and more with power tools, particularly drills, impact drivers (and pretty much anything Festool handheld).

We know brushless is meant to be better – same power with a lower voltage battery, and/or longer run time, longer durability of the motor.  But why?  What makes a brushless motor so ‘special’?  And if it is so great, why do we have brushed motors in the first place?  This will be a pretty simplistic look at the concept – there is plenty of info out there if you want greater detail!

Let’s start with the last point.

Brushless motors require electronic control, so it is only with the inclusion of a modern microprocessor has it been possible to build such a motor.  Still, they have been around since the early ’60s, so perhaps a little strange they are not more common (cost does play a factor).  They have only been becoming reasonably common in some tools in the past 5 years or so.  Perhaps why they are so good is still not really appreciated.

In simple terms, a canned motor (or brushed) has a rotor at the centre which is an electromagnet.  Power has to get to that electromagnet, which is done via ‘brushes’ that brush against contacts on the rotating body.  Around the outside is the stator, made up of permanent magnets.  (Stator => Static/stationary is how I remember it.  Rotor => rotating)

Brushed Motor

Brushed Motor

The brushes are rubbing continuously on the core (the rotor) (at a point called the commutator fwiw).  Brushes wear, there is friction, heat.  A typical brushed motor is around 50% efficient, even down to 30% on smaller motors.  That means an 18V brushed motor power tool (if looking at cordless versions for a sec) is getting 9V worth of power from the motor. (Even as low as 5.5V)

Triton Router Brush

Triton Router Brush

Triton Rotor (image from http://www.horizontalheavens.com)

Triton Stator (image from www.horizontalheavens.com) - static electromagnets typically replace the permanent magnets in AC motors

Triton Stator (image from http://www.horizontalheavens.com) – static electromagnets typically replace the permanent magnets in AC motors

A brushless motor swaps the operation of the rotor and stator.  The rotor is now a permanent magnet, and the stator is the electromagnet.  As it is not rotating, getting electricity to it is easy – no brushes required.

Brushless Motor

Brushless Motor

Electronics control the switching on and off of each electromagnet around the stator, causing the rotor to, well, rotate.

A brushless motor is around 70% efficient, so in the same cordless scenario above, a 13V tool as a cordless model is about the same power as a good 18V brushed motor one.   So, for example, you take my 14.4V Festool brushless impact driver that I got from Ideal Tools recently, and put it up against an 18V cordless model (with a brushed motor (Hitachi, Milwaukee etc etc)), and the Festool is going to kick its butt 🙂  Not that Festool are the only brand with brushless motors, both the aforementioned brands also have brushless versions – but it is definitely worth making sure that the tool you are buying does. And the brushless aspect makes a lot more difference than the battery voltage as you can see.  Once you have electronic control in the tool, you can do all sorts of other smart things, like Festool’s ECS controls not only the motor’s speed, but also provides overload protection and controls the electronic clutch to boot.

Even in a corded model, you are looking at less wear, a lighter tool (for the same power), a quieter motor, and electronic controls of other functions.

Brushless vs Brushed

Brushless vs Brushed

One is spinning as freely as possible, (you still have bearings etc in both types of course).  The other is like driving with the handbrake on.

One Response

  1. Thank you for that Stu
    Having had much more experience with brushed motors, it has certainly been an eye opener, looking at several brushless units recently. The efficiency & quietness of the Powermatic machines at their Carbatec launch and just how well brushless motors perform, whilst checking out a demo Dewalt compact impact driver recently, as well.
    Now if only someone could come up with a retrofit brushless motor kit for the Triton router, what an awesome bit of kit that would be!
    Well, I can dream can’t I? – 🙂

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: