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Brushless Motors vs Brushed Motors


Bingobelle

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What is the cons and pros with a motor without brushes?

Some makers like hitachi says it is so good because you do not have to change the brushes and therefore save some time. I had my older dewalt dc7** something for 5 years and never had to change brushes. My dcd 960 is one year old now and I´m using it nealry everyday and there is nothing wrong with the brushes, and proberly will not be for a lojng time. And by the way, chanhing brushes take like 5 minutes. Well, you have to order them first and that might take some time, so guess they have some point there.

Hitachi for example claims longer runtime and more torch because the use of no brushes, but for what I know the DCD960 or 970 is stronger than any of the hitachi drills. Maybee I´m wrong.

Any expert here knowing some facts?

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There is a long list of Pro's and Con's. It can mostly be simplified to cost. It's simply not cost effective in mainstream power-tools.....yet.

A DC Brushless Motor uses a permanent magnet external rotor, three phases of driving coils, one or more Hall effect devices to sense the position of the rotor, and the associated drive electronics. The coils are activated, one phase after the other, by the drive electronics as cued by the signals from the Hall effect sensors, they act as three-phase synchronous motors containing their own variable frequency drive electronics. 

BLDC Motor Pros;

•Electronic commutation based on Hall position sensors

•Less required maintenance due to absence of brushes

•Speed/Torque- flat, enables operation at all speeds with rated load

•High efficiency, no voltage drop across brushes

•High output power/frame size.

Reduced size due to superior thermal characteristics. Because BLDC has the windings on the stator, which is connected to the case, the heat disipation is better

•Higher speed range - no mechanical limitation imposed by brushes/commutator

•Low electric noise generation

BLDC Motor Cons

•Higher cost of construction

•Control is complex and expensive

•Electric Controller is required to keep the motor running. It offers double the price of the motor.

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A Brushed Motor has a rotating set of wound wire coils called an armature which acts as an electromagnet with two poles. A mechanical rotary switch called a commutator reverses the direction of the electric current twice every cycle, to flow through the armature so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the motor. As the poles of the armature electromagnet pass the poles of the permanent magnets, the commutator reverses the polarity of the armature electromagnet. During the instant of switching polarity, inertia keeps the classical motor going in the proper direction. 

 

Brushed Motor Pros;

•Two wire control

•Replaceable brushes for extended life

•Low cost of construction

•Simple and inexpensive control

•No controller is required for fixed speeds

•Operates in extreme environments due to lack of electronics

Brushed Motor Cons;

•Periodic maintenance is required

•Speed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torque

•Poor heat dissipation due to internal rotor contsruction

•Higher rotor inertia which limits the dynamic characteristics

•Lower speed range due to mechanical limitations on the brushes

•Brush Arcing will generate noise causing EMI

Courtesy of Dynetic.com

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on the paper a nonbrush motor look better and for sure it is a more modern and "refined" motor.

The problem with heat I think Dewalt have taken good care of with the no can design they use. The air goes nicely throw the engine so I do not think that is a problem, at least on no can motors.

The more complex electronics coming with the nonbrush motors I think can be of greater concern. Actually if you think about how it can look on a worksite and the hard enviroments the drill suffer from nearly everyday. Proberly that will be a bigger problem than worn out brushes. However, more tourch and a quiter drill is always nice and actually the DCD960 is quit noisy. Both from the all metal gearbox with metal body and also the engine sounds much.

Personally I think I rather have a less complicated drill that you at least can asume will last longer on the "battlefield" and changing brushes every 5 years or so I do not see as a problem.

But if the drill will work in less brutal enviroments I think the brushless motor can be a very good choise. I found for example the DCD970 a typical constuctor site drill ( brutal enviroments ) and for example the festool t15 more a drill for building kitchen and stuff like that. ( more elegant work )

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