Please forgive my lack of education however, I have a question. We have all been inundated with brush-less technology lately.Is this for DC battery operated components only? How about brush less for tools like an ac powered drill press, just to get the ball rolling?Is this even an issue? I do not even know if an ac electric motor has brushes.Can someone enlighten me?Thanks, Ken
Brushless
- Thread starter Kenskip1
- Start date
Brushless DC motors work like AC motors... except the magnetic filed has to be rotated manually(electronically). By its nature, alternating current supplies its own means of rotating the magnetic field... brushed AC motors exist but are uncommon... and then you have universal motors... which are a sort of hybrid.
what are all the portable power tools using? just about every portable drill, saw, sawzall, router, etc. I own has brushes, every HF power tool I ever bought comes with spare brushes. not talking cordless, regular power tools. I thought brushed A/C motors were the norm?
edit: I am going to assume they must be universal motors then since no capacitors involved?
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kctyphoon
Banned
Unless there is something I've missed that "technically" disqualifies them, brushless motors ARE ac motors.
kctyphoon
Banned
Brushed AC motors are the norm with corded power tools... It's brushless cordless tools that they are speaking about.. They are DC powered with ac motors that are digitally controlled..
hsvtoolfool
Well-known member
^^^This.
Here's a couple of fun videos on the subject from one
of my favorite 'Toobers...
Brushed DC motors:
AC induction motors:
I like this guy because he has no fear. A 12" jointer made
from birch ply? Sure I can make one.
kctyphoon
Banned
just to add - ill take a leap here and write the reason you dont see "brushless" corded tools is because basically your dealing with a limitless power supply, and its just alot cheaper and easier to throw a slightly larger "brushed" motor on a tool than it would be to put all that r&d into a brushless version. if the end result can be achieved with spending less money, then why even bother with making a harder design..
brushless cordless enables increased runtimes, and higher torque ratings which is an advantage because they are working to get the most out of a single battery platform. with batteries getting lighter and smaller every few years, it only made sense for companies to start improving on motor design and efficiency.
i really dont think seeing 15 amp hour battery packs for certain cordless tools is that far off in the future...
brushless cordless enables increased runtimes, and higher torque ratings which is an advantage because they are working to get the most out of a single battery platform. with batteries getting lighter and smaller every few years, it only made sense for companies to start improving on motor design and efficiency.
i really dont think seeing 15 amp hour battery packs for certain cordless tools is that far off in the future...
theoldwizard1
Well-known member
Well ... sort of/kind of ...
A brushless motor uses pulses of electricity, not a continuous sine wave. They COULD use a sine wave if the FREQUENCY of the sine wave could be easily changed (a brushless motors speed is proportional to the frequency of the pulses of sine wave peaks).
It is VERY IMPORTANT that the motor speed and the frequency of the driver stay synchronized ! That is why there is a speed sensor (actually, it is a position sensor) on the motor. It also requires a microprocessor (small, cheap) or other electronics to maintain this synchronization. If the motor slows down (from a load) the pulses must slow down.
Interest footnote. Most brushless motors are "outunners". This means the output shaft is connect to a cup where the magnets are attached. It is easier to glue the magnet to the inside of the cup that is spinning around the various coils of wire that are being energized. The big win in the early days was no brush drag or wear. Very strong magnets and cheap electronics brought the technology to portable hand tools.
As mentioned, there are lots of good videos on YouTube about this.
oldldh
Well-known member
guy48065
Well-known member
A DC motor delivers full rated torque at zero or low rpms so they're great for screwdriving & hole boring. An AC induction motor delivers its max torque at full speed. I don't understand why anyone would want a powerful brushed DC tool to run like a weak AC tool...
I'll keep my brushes & slotted commutator over the microprocessor-controlled gadgetry required to chop that DC & create the spinning field needed to move the rotor, thank you.
I'll keep my brushes & slotted commutator over the microprocessor-controlled gadgetry required to chop that DC & create the spinning field needed to move the rotor, thank you.
theoldwizard1
Well-known member
"If it works, don't fix it !" Especially if it is already PAID FOR !!
1990 Grand Wag
Well-known member
Question (just for my education), didn't the now discontinued Porter Cable/DeWalt low profile random orbital sander have some "sort of" brushless motor (although it was corded)?
Not sure if OP questions were answered so I'll take a crack at it.
Brushless is more efficient than brushed due to elimination of the friction of dragging brush across rotating commutators. More powerful the motor, higher the brush pressure, more frictional loss.
As stated, it takes more auxiliary circuits to drive brushless DC motor and it runs at higher rpm. But the efficiency gained offset the added complexity. Especially as more power is generated by the motor.
As for corded motors, since % efficiency gain isn't the top concern and slower turning A/C induction motor is suitable, brushless DC motor isn't used. I hope my response isn't too redundant.
Brushless is more efficient than brushed due to elimination of the friction of dragging brush across rotating commutators. More powerful the motor, higher the brush pressure, more frictional loss.
As stated, it takes more auxiliary circuits to drive brushless DC motor and it runs at higher rpm. But the efficiency gained offset the added complexity. Especially as more power is generated by the motor.
As for corded motors, since % efficiency gain isn't the top concern and slower turning A/C induction motor is suitable, brushless DC motor isn't used. I hope my response isn't too redundant.
theoldwizard1
Well-known member
I always wondered what the motor shaft RPM difference was between brushed and brushless tools, say 3/8" drills. Both are geared down so you can not tell just from the chuck speed.