What is inside a hair dryer (Part - 2) - Electrical Engineering Video Lecture

Let's take a look at
the hair dryer itself.
And as we come up
the plug, here, this
is where the power comes in.
We have another
protective rubber piece
and a little holder
here that's molded in,
which is kind of nice.
So you can hang your
hairdryer in the bathroom,
if you want to.
And then, we have our switch.
So this allows us to turn
the power high, low, and off.
And we have these little
molded patterns, here.
And then our funnel, that
funnels the air through.
And you can see there's
a screen on the back.
And that helps to
keep things out.
So let's take a look
at what's inside.
We're going to use a Phillips
head screwdriver, here.
And just remove these screws.
These screws are plated.
They're made out of steel.
And I believe they
are chrome plated
because they're super shiny.
And the reason
they would do that
is that hairdryers
are often used
in very moist environments, like
bathrooms and things like that.
And so the screws, if
they're made out of steel,
are going to rust.
And so you want to put a
coating on them that won't rust,
and chrome won't rust.
So that protects them.
And because those
screws are visible,
they may have also used
a bright finish chrome
because it looks better than,
say, a painted screw would.
OK, so let's take this apart.
And it also provides a little
better corrosion resistance
than paint does.
All right, so let's
take this apart, here.
And if you look
on the inside, you
can see that, again, this
was an injection molded part.
The mold came
together, like this.
And plastic was injected.
And then, injector pins-- which
you can see the little marks
right here-- pushed on the
part and caused it to drop out.
And you can see that this
material is called PP.
It stands for polypropylene.
And the ejector pin
marks are right here.
So they're scattered
throughout this,
to evenly push on it,
to get it to come out.
There's all these
features on the inside.
They provide structural
rigidity and stiffness.
They also provide a mounting
location for the fan housing,
here.
And the screen in the
back looks like it
was put on with a
machine, pressed
against the back of the housing,
here, where there's the vent.
And it looks like the
plastic was heated up.
And the screen was pushed
into the heated plastic,
so it's held in place.
And that's kind
of a low cost way
to hold those pieces together.
There's no fasteners there.
Fasteners add expense.
So that's one of the ways
they were able to reduce cost.
So we'll set that aside,
for just a second.
And if we come up, we look
up inside the switch here.
This is where the
power comes in.
This part, right here, is
very interesting, as well.
A lot of times you'll
see manufacturers
will actually tie the
power cord in a knot.
And in this case, there,
they're not tying it in a knot.
They run it through
over this screw boss,
or place that the screw goes in.
And the reason why
they do that is
so that you can't pull it out.
And you definitely don't want
to have a condition where
the wire can get pulled
away from the switch
and maybe have a free
electrical contact in there that
could touch things, and
short out, and maybe just
cause your hairdryer
to stop working.
So that protects you there.
So that's another safety thing.
So we'll go ahead and
pull this switch out.
You can see that these
are plastic brackets
that the switch
fits nicely into.
It holds it steady, in place.
And the switch has three
different settings.
And let's see if we get that
to where you can see it.
The switch is 16
amps at a 125 volts,
or eight amps at 250 volts.
So this switch can handle
a fair amount of current.
And if you see, there's a number
of different wires leading out
from the switch.
And they run to the heater.
And this wire, right
here, is connected
with this brass connection.
And since the
connection is open,
there's a clear piece of
plastic that's gone over that.
And that prevents it from
contacting the other parts
of the switch and
shorting out the circuit,
or creating a problem.
So we have another little
tiny screw, right here.
We're going to take
that screw out.
And it's the backside
of the switch, here.
And so that held the front
side of the switch in place.
That's just, again, an injection
molded piece of plastic.
And then, the backside
slides in this channel,
right here, like that.
And it interfaces with
the switch itself.
And it's just a piece
of molded acrylic
that fits against
the switch and allows
you to transfer the
movement from the outside
to the inside of the unit.
All right, so we've
got a fan here.
We've got these two
santoprene pieces.
They're just like rubber
molded accent pieces.
And I think they're mostly
there for just design style.
And we're going to go
ahead and pull this out,
see if we can get
the heater unit out.
Before we take a look at
that, let's look at this.
So this is our funnel.
And as you know, the
hair dryer heats up.
So that heat could
cause the plastic
to get really hot, or soft.
And so, they put
this piece, in here.
And this is called a mica sheet.
And it basically
protects the housing
from getting too hot
when the heater heats up.
And then if you look
on the backside here,
we've got a bracket,
a little cover.
And this is made out of steel.
It's just painted steel.
And again, it protects things
from getting into the heater.
It just force fits into
the end, down there,
so there's no fasteners.
Again, it helps to reduce costs.
This was injection molded,
just like this piece was.
And the mold came together
like this, from both sides.
And then there were pins
that pushed the plastic out
once it had hardened.
And so that's that.
So if we take a
look here, we can
see that we've
got nichrome wire.
So the thing that's fascinating
about this hair dryer
is that they take
this nichrome wire,
and they use it as
a massive resistor.
Because your motor doesn't
want the full 120 volts
AC that comes in
from the outlet.
It wants DC power.
It needs to run on DC power.
It needs to run on 12 volts.
So the way they get it
down to 12 volts is they
use the heater as a resistor
to drop the voltage down
to 12 volts.
So that's kind of an
ingenious way of doing that.
And then, the heater is made
out of these coils, here.
And they're called
nichrome wire,
or they're made out of
material called nichrome wire.
And nichrome is an alloy
of nickel and chromium.
And when electricity is run
through it, it heats up.
And it heats up in a way that
is very effective at getting hot
when powers run through it.
But it also doesn't oxidize.
So a lot of times when
you heat up other metals,
they'll oxidize, they'll rust.
And then you get
problems with that.
This doesn't do that.
It just heats up, and
then it cools back down
and there's no oxidization.
So it works really
well as a heater.
And on the front,
here, you can see
there's this 90 degree opposed
bracket that holds everything
90 degrees apart, which
keeps everything working
as far as air flow
and stuff like that.
It also holds this
mica sheet separated.
And then you can
see on the inside,
we have these brass contacts.
And they're little brass rivets.
And they distribute the power
around to different parts
of the heater.
And right here, this part
is a bimetallic strip.
So that bimetallic strip is
made out of two pieces of metal.
And what it does is
when the metal is heated
to a certain point, it causes
the bimetallic strip to bend.
And so one piece of metal has
a different expansion rate
than the other piece of metal.
And it causes the strip to bend.
So maybe, this one on
the outside-- if this
was the bimetallic strip.
This one expands
faster than this one,
and it causes it to bend.
So you could have two
different types of metal
like, say, an alloy called
invar and another piece of metal
called copper.
And the copper is
going to respond
to heat at a certain rate,
and it's going to expand.
And the invar is going to
not expand nearly as fast.
And it's going to cause
that switch to open up.
And that will shut down
the power to the heater.
So if it gets too hot, the
bimetallic strip will expand,
and it will pull itself
away from the contact
and shut down the
electricity to the heater.
You can see, we also have a
diode, right here, in line.
That just controls the
flow of electricity. .
It's like a little
electrical valve.
And then we have a
thermal resistor, here.
I'm sorry, a thermal fuse.
This is called a thermal fuse.
And the thermal fuse, basically,
is another safety precaution.
If temperatures get too
high, the fuse will blow.
And it will shut
down the hair dryer
and prevent the housing from
melting, or the hair dryer
from getting too hot and
potentially blowing air out
that could burn you.
And so, remember, the heater
has functioned as a resistor.
And it has dropped the
voltage down to 12 volts.
But it's still AC power, which
means alternating current.
Alternating current, basically,
functions as a sine wave,
like this.
It flows back and forth.
And the motor that
we have here is
designed to run
on direct current,
so just flowing in
a continuous loop.
And the way that this
unit, this hair dryer,
deals with that is it
has these four diodes.
You can see them--
one, two, three, four.
And so what those
four diodes do is
they function like
a bridge rectifier.
And they convert the
AC power into DC power.
And they do it in a
very low cost way.
The diodes are very inexpensive.
So once the voltage is dropped
and the power is converted,
the fan begins to spin.
And so, the fan turns.
And it pulls air in.
And you can see these
louvers, right here.
They help with the
air flow, so that it
blows past the heater
in the right way.
And the inside of
the motor-- I'm
not going to take the
motor apart in this video.
We'll do that in another one.
But inside the motor
is a copper winding,
and there are some magnets.
And the electricity
causes the motor to spin.
And it pulls air
through, past the heater.
And the reason why you do this
is that heated air, or hot air,
can hold a lot more
moisture than cool air.
So it dries your hair
a lot more quickly.
Old hair dryers used to be
about 100 watts, or maybe just
a little bit more than that.
So it took them a long time to
dry your hair because they just
didn't have the same amount of
heat energy that this one does.
At 1,875 watts, this is
about as much heat energy
as you can generate in
a given 20 amp circuit.
So it's pretty
close to the limit.
In any case, this is,
again, a plastic propeller.
And it looks like an
acrylic housing, here,
or clear plastic housing.
And then we have another bezel.
And this just helps
to direct the air flow
and also hold the
motor in place.
But that's the Conair
1875 hair dryer.
And I hope you've enjoyed it.