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Looks like brushless motors are more convenient - no brushes means no maintenance required. For example, power tools manufacturers often cite that graphite brushes need to be replaced every 50 hours of continuous use. I'd think that this alone should make brushless motors much more convenient. Still most power tools use brushed motors.

What's the reason to use brushed motors instead of brushless motors?

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    \$\begingroup\$ Also one should remember incredible level of EMI near brushed motor :-) \$\endgroup\$ – BarsMonster Jun 20 '11 at 15:05
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Because they are cheaper and lower-tech - no need for tricky semiconductor devices. Also, switching electronics for high-power devices (1-5kW+, 1000V+) is tricky to implement (but nothing modern electronics can't handle).

Sometimes companies produce crap just because it's cheaper & gives some long-term income on maintenance, or they just have 50 years old production line deep in China's village which is nearly free to operate.

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  • \$\begingroup\$ No! Brushless motors of any construction do not have the power output per weight of a brush-motor. So , for drills, tools or vaccum cleaners and the like this motors will be used for the time to foresee. \$\endgroup\$ – Georg Jun 20 '11 at 15:50
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    \$\begingroup\$ @Georg : BLDC motors offer several advantages over brushed DC motors, including more torque per weight, more torque per watt (increased efficiency), increased reliability, reduced noise, longer lifetime (no brush and commutator erosion), elimination of ionizing sparks from the commutator, and overall reduction of electromagnetic interference (EMI). en.wikipedia.org/wiki/… \$\endgroup\$ – BarsMonster Jun 21 '11 at 8:13
  • \$\begingroup\$ Also, Power/Weight efficiency of brush-less motors is the main reason why this is nearly the only motor type used RC planes of any size. Also, I just cannot see why we can lose power if we let magnets rotate instead of coils. \$\endgroup\$ – BarsMonster Jun 21 '11 at 8:16
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    \$\begingroup\$ Yeah, but brush-less motors win both at power/watt AND power/weight. They lose only in price :-) \$\endgroup\$ – BarsMonster Jun 21 '11 at 9:47
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    \$\begingroup\$ @Georg: I don't know where you got the idea from that brushed motors have a better power to weight ratio than brushless. It's just plain wrong. The electronics does add some size and weight, but then again so do the brushes and the mechanics to house them. At worst the electronics could do dumb commutation just like brushes do, but the option is there for better. If you notice, size and weight constrained applications are the ones leading the use of brushless. Old fashioned brushed is simpler with no electronics required, so can be cheaper when you're not paying for the extra maintenance. \$\endgroup\$ – Olin Lathrop Jun 27 '11 at 21:15
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A brushed motor can be driven with direct current, while a brushless motor requires the drive current to be electronically commutated. The electronics for this add cost and complexity.

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  • \$\begingroup\$ Ah, this is very important, because there are so many of mains systems with DC! \$\endgroup\$ – Georg Jun 20 '11 at 15:46
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    \$\begingroup\$ Many power tools are driven by batteries. \$\endgroup\$ – Colin K Jun 20 '11 at 16:35
  • \$\begingroup\$ That is all the same! Those motors were/are called "Universal Motor" because by construction one could use them on Edison DC nets as well as in AC nets. Only for rather big motors (some kW order) there is difference, and DC/AC switching was no longer possible. \$\endgroup\$ – Georg Jun 20 '11 at 17:57
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    \$\begingroup\$ @Georg why don't you post an answer yourself? You can't seem to be happy with any of the others'. I'd like to hear more about these universal motors, for as far as I knew there is quite a bit of a difference between DC and AC motors. \$\endgroup\$ – leftaroundabout Jun 20 '11 at 20:17
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    \$\begingroup\$ @Georg: don't confuse "level" and "topic." The level of a question has nothing to do with whether it is on or off topic. I'm checking with the electronics.SE people to see if they would like this question. \$\endgroup\$ – David Z Jun 20 '11 at 22:04
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Why do we have brush motors? Mainly because they are cheap and easy to construct. I can (and have, on multiple occasions) constucted a brushed DC motor with nothing more than cheap wire, thread or tape, a paper clip, a scrap of wood, and thumb tacks. A cheap permanent magnet makes things easier but is not necessary.

Also, as Georg partially pointed out, you get higher (power/weight) with brushed motors.

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Others have covered servicing and cost issues well .There is still a place for the brushed motor when it has a series would field .Remember that BLDC motors have rotating permannet magnets which are not as strong as an electromagnet .This means that the BLDC motor wont make as much torque and its characteristics are more like a shunt wound motor.The BLDC motor can spin much faster without flying apart due to its simple robust rotor so if you gear it down you can get the torque back.Most electric motors are thermally limited so the better cooling characteristics of the BLDC combined with higher RPM give a higher continious horsepower rating.However the peak torque of the series wound brushed motor is greatest .This is why the electric drag people use them and win .I guess that if reduction gearing is not an option then the series brushed motor is useful.

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