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I have this motor here, and imagine being
able to plug it into your house outlet
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using alternating current or a direct current
power source.
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Today I'm going to tell you what a universal
motor is and how it works.
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What's up Lovers of
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Engineering, my name is Igor Felipe and I'm
going to tell you a story that
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happened here on the channel a few days ago.
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I was taking apart a
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washing machine that didn't work anymore and
I came across this engine here and I was thinking
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about what
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I could do to take advantage of it.
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But for that I needed to understand
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how this engine worked.
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So I called my brother Gustavo,
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who is an electrical engineer, and asked what
kind of engine that was.
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He looked, saw that here at the top there
is a system of carbon brushes and commutators
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and said
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“Igor, this looks like a direct current
motor”.
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But one thing didn't make sense,
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because the motor was plugged directly into
the socket that uses alternating current.
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Well, what we thought at the time was, there
must be some rectifier system in the six-pack.
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And we continued to dismantle, and to our
surprise we found nothing.
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And there was only one way to find out, really.
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Using the best sparrow professor spirit,
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we took the motor and plugged it directly
into the alternating current, and of course,
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the motor ran.
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But the constructive form of this motor is
very reminiscent of a direct current motor,
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so why not test it?
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And to our surprise,
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the motor also works using a DC power supply.
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It looks like magic right?
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But this is nothing more than a universal
engine.
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The universal motor is a type of electric
motor that can operate on either alternating
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current
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or direct current power and uses an electromagnet
as its stator to create its magnetic field.
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It is a series wound motor and uses a commutator
where the coils that produce the stator magnetic
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field
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are connected in series with the rotor windings
through a commutator and
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therefore produce high starting torque.
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Basically, if we look closely, what generates
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the magnetic field is not static magnets as
we usually see in direct current motors,
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but a coil, and it is this coil that generates
the magnetic field.
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The universal motor is very similar to a direct
current motor in construction,
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but it is slightly modified to allow the motor
to work properly also on
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an AC supply.
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This type of electric motor can
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operate well on alternating current because
the current passing through the coils that
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produce
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the magnetic field and the armature will alternate
its polarity synchronously with the supply.
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Therefore, the resulting mechanical force
will occur in a consistent direction of rotation,
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regardless of whether you reverse the voltage
cables, because what determines their
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direction of rotation is the way we mount
the switch and the polarity of the field coils.
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That is, no matter how you place the plug,
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the motor will always rotate in one direction.
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That's why universal motors are often
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built into the device they are supposed to
drive.
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Most universal motors are designed
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to operate at higher speeds, in excess of
3500 RPM.
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They run at a lower speed when powered by
direct current.
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Want to see this up close?
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If we connect this motor to alternating current,
that is,
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to the outlet in your house, the motor will
work that way with a very large rotation.
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Note that no matter how I plug in the plug,
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the motor always rotates in the same direction.
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Now if we use a direct current source,
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notice that the motor turns much slower.
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And again, no matter which position you connect
the DC wires to,
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the motor will always rotate in the same direction.
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But how is a Universal engine built?
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Building a universal motor is very
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similar to building a direct current machine.
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It consists of a stator on which the field
poles are mounted.
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The coils that generate the magnetic field
are wound around these field poles.
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However, the entire magnetic path which is
the stator field circuit
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and also the armature is laminated.
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Lamination is necessary to minimize
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eddy currents that can induce the motor when
operated on alternating current.
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The rotating armature is of the wound type
with straight or angled slots and uses
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a commutator with brushes resting on it.
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Commutation in alternating current tends to
be
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poorer than in direct current due to the current
induced in the armature coils,
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so the brushes used in this type of motor
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need to be of high resistance.
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And how does this engine work?
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When the universal motor is supplied with
direct current supply,
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current flows in the field winding, producing
an electromagnetic field.
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The same current also flows from the armature
conductors.
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When a current conductor is placed in an electromagnetic
field,
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it experiences a mechanical force.
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Due to this mechanical force, or torque,
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the rotor starts to rotate.
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The direction of this force is
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given by Fleming's right-hand rule.
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When powered with alternating current,
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it still produces unidirectional torque.
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As the armature
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winding and field winding are connected in
series, they are in the same phase.
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We know that here in Brazil, our network works
with a frequency of 60 hertz,
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that is, it switches 60 times per second.
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Therefore, as this frequency
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changes periodically, the direction of current
in the armature and field winding
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reverses at the same time.
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Thus, the direction of the magnetic field
and the
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direction of the armature current are reversed
such that the direction of force experienced
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by
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the armature conductors remains the same.
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So regardless of the power supply,
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whether it is AC or DC, the universal motor
works on the same principle as the DC series
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motor.
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And what are the characteristics of this type
of engine?
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The speed and load characteristics of a universal
motor
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are similar to those of a DC series motor.
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The speed of a universal motor is low when
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used at full load and very high at no load.
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That is, when we connect it to a device
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such as a drill, and we are going to use the
drill to drill a wall,
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increasing the load on the rotor
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, the tendency of the motor speed is to decrease
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. maintain or increase speed.
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We have a video that talks about gears,
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and if you want to understand a little more
how such a system works, I'll leave a
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card for that video at the end of this one.
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And where do we use this type of engine?
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Universal motors are used in various home
appliances such as vacuum cleaners,
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mixers, household sewing machines, six packs
and many other uses.
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The highest rated universal motors are even
used
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in drills or blenders.
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A negative aspect is the
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maintenance and short life problems caused
by the commutator, this is because we have
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a great
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friction of the brushes with the commutator.
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We may also have problems with
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electromagnetic interference or EMI due to
any spark that occurs.
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Due to the commutator brushes, universal motors
are more suitable
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for devices that are used sporadically and
that require a high starting torque,
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such as blenders and drills for example.
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Another negative is that these engines
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can only be used where predominantly clean
air is present at all times.
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Due to the risk of overheating, these types
of motors usually have fans on the
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rotating shaft itself to cool the system,
so having such a
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fully sealed and closed motor is impractical.
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That's why we can always see some opening
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or air intake in devices that use the universal
motor to
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force cool these devices.
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And as it needs a fan to induce
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air to pass through it, it ends up losing
some efficiency due to the drag that the propellers
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generate, as it ends up expending part of
the turning energy to do its own cooling.
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Is that you?
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Do you have any items in your house that have
a universal motor or have you encountered
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such a motor when disassembling some equipment?
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Leave it here in the comments I want to know.
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I'm going to leave two videos here that you
might like too,
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so take the opportunity to check out one of
them.
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This is your time to like
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the video, subscribe to the channel and activate
the notification bell.
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And that my friends, a big hug and see you
in the next video
