3 Heat switch.
I test a 3 heat switch and find that in the low position and medium position one of the terminals is common. What would I connect this terminal too and why?...
Simmerstat.
What is the function of the heating element in a simmerstat?....And If I use my ammeter to test across it, what reading am I likely to get ohms or Kilo-ohms?..
Motors.
I've wired up a motor and connected it to a conveyor that needs to go from left to right. But instead it goes the opposite direction. Why is this and how would I change the wiring to have the motor turn the opposite direction?.
Appliance testing.
I've tested a class one appliance, And have found that when I connect my meter between earth and the metal case I get 5 ohms. Is this safe to use?...If so why?..And if not why?...
Protection.
I have a bench grinder with a powerful ac motor in it. I have blown the fuse when using it.
From the label printed on it I have calculated that it draws 5.5 amps. But when I use a 6 amp fuse it keeps blowing. Why would this happen when the fuse is rated higher than the current drawn by the appliance?.
Monday, November 8, 2010
Conductors and insulators..
Here are a few common examples of conductors and insulators:
- Conductors:
- silver
- copper
- gold
- aluminum
- iron
- steel
- brass
- bronze
- mercury
- graphite
- dirty water
- concrete
- Insulators:
- glass
- rubber
- oil
- asphalt
- fiberglass
- porcelain
- ceramic
- quartz
- (dry) cotton
- (dry) paper
- (dry) wood
- plastic
- air
- diamond
- pure water
One simple formula we use is how we can calculate the resistance of a conductor so we know how big of a cross-sectional area or how long out conductors can be to carry our electrical loads.
We can do this by using the formula.
Ac Motors and induction.
A Shaded Pole AC Motor
Here is a photo of a typical shaded pole motor. See the close-up of the notch in the laminations and the extra heavy winding of two turns creating the phase difference between the two sections of the laminations, giving the magnetic field a directional motion. The rotor spins CW as seen from the end with the screw on the shaft. Motors like this are used in thousands of applications.
Another Shaded Pole AC Motor
Here is a photo of a ceiling fan motor, also shaded pole, but with six windings instead of only one as seen above. The rotor laminations are skewed to provide smoother torque. The pole pieces with the windings have a slot in them to create a delayed flux, creating a direction for rotation.
Exploded View of an AC MOTOR.
Below is an exploded view of the AC motors similar to what we have been testing. This is a great photo as it shows all the working parts.
What Spins an Electric Motor ?
The rotor of an electric motor needs a torque to start it spinning. This torque is
normally produced by magnetic forces, exerted between magnetic poles on the
rotor and those on the motor’s stationary shell. Attractive or repulsive forces pull
or push on the outside of the rotor, producing torques that make the rotor spin
faster and faster until friction or the objects attached to it reduce its net torque to
zero. After that point, the rotor turns at a steady angular velocity.
Both the rotor and the motor’s fixed shell are magnetic. The forces between
these magnets are what produce the torques. But while permanent magnets are
often used in electric motors, at least some of a motor’s magnets must be electromagnets.
That’s because the motor can only keep turning if some of its magnetic
poles change or move as the rotor spins. That way, while the rotor turns to bring
opposite magnetic poles as close together as possible, the poles keep changing or
moving so that the rotor finds itself perpetually chasing the optimum arrangement
of poles.
Here is a photo of a typical shaded pole motor. See the close-up of the notch in the laminations and the extra heavy winding of two turns creating the phase difference between the two sections of the laminations, giving the magnetic field a directional motion. The rotor spins CW as seen from the end with the screw on the shaft. Motors like this are used in thousands of applications.
Another Shaded Pole AC Motor
Here is a photo of a ceiling fan motor, also shaded pole, but with six windings instead of only one as seen above. The rotor laminations are skewed to provide smoother torque. The pole pieces with the windings have a slot in them to create a delayed flux, creating a direction for rotation.
Exploded View of an AC MOTOR.
Below is an exploded view of the AC motors similar to what we have been testing. This is a great photo as it shows all the working parts.
What Spins an Electric Motor ?
The rotor of an electric motor needs a torque to start it spinning. This torque is
normally produced by magnetic forces, exerted between magnetic poles on the
rotor and those on the motor’s stationary shell. Attractive or repulsive forces pull
or push on the outside of the rotor, producing torques that make the rotor spin
faster and faster until friction or the objects attached to it reduce its net torque to
zero. After that point, the rotor turns at a steady angular velocity.
Both the rotor and the motor’s fixed shell are magnetic. The forces between
these magnets are what produce the torques. But while permanent magnets are
often used in electric motors, at least some of a motor’s magnets must be electromagnets.
That’s because the motor can only keep turning if some of its magnetic
poles change or move as the rotor spins. That way, while the rotor turns to bring
opposite magnetic poles as close together as possible, the poles keep changing or
moving so that the rotor finds itself perpetually chasing the optimum arrangement
of poles.
Induction AC Motors
Some alternating current motors have rotors that are neither permanent magnets
nor conventional electromagnets. These rotors are made of non-magnetic metals
such as aluminum and have no electric connections. But their electric isolation
doesn’t keep these rotors from becoming magnetic. When an aluminum rotor is
exposed to changing magnetic fields, currents begin to flow through it and these
induced currents make the rotor magnetic.
Motors that use induction to create magnetism in their rotors are called induction
motors. Induction motors are probably the most common type of AC
motor, appearing in everything from household fans to industrial pumps to cable-
lift elevators. They provide lots of torque, start easily, and are inexpensive.
An induction motor works by moving a magnetic field around the rotor.
The stationary shell surrounding the rotor contains a sophisticated electromagnet
called a stator. While the stator doesn’t move, the field it produces does. Through
a clever use of various electromagnetic devices, the stator is able to create magnetic
poles that move in a circle and travel around and around the rotor.
Saturday, October 9, 2010
Electric motors and induction.
We use Electric motors for everything, almost every mechanical moveing electrical appliance is caused by an AC (alternating current) or DC (direct current) electric motor.
A simple motor has six parts:
- Armature or rotor
- Commutator
- Brushes
- Axle
- Field magnet
- DC power supply of some sort
An electric motor uses magnets and magnetism to create motion. Magnets have two poles and work in the way that, Opposites attract and likes repel. Inside an electric motor, these attracting and repelling forces create rotational motion.
Above is an image showing the main parts of a motor in a simplified Diagram. Using the green coiled wire (usually always made of copper) we pass a current. When the current passes through the coil induction happens and between the coils we get an invisible magnetic field. This field then reacts with the two magnet poles on either side and one end of the commutator will be attracted to one end of the magnet pole. And likewise as I explained before with opposites attracting and likes repelling, The opposite end of the commutator will repelled by the opposite pole of the magnet. And due to the construction of the commutator within the housing it will begin to turn dude to the attracting and repelling forces of the magnetic field.
Thursday, August 12, 2010
About me.
Hi My names Elliot brooks. I'm studying The Certificate in applied Technology Audio Visual technician here at Unitec.
I hope to one day work in Home theatre and Home/Corporate Automation. I'm using this course to enable me to gain some experience in Audio Visual so I can get employment and then start my progression to where I want to be within the industry..
I also like to Travel and have lived and worked in The U.S the U.K and Australia. I hope to use my employment within A/V to work overseas in the future.
I hope to one day work in Home theatre and Home/Corporate Automation. I'm using this course to enable me to gain some experience in Audio Visual so I can get employment and then start my progression to where I want to be within the industry..
I also like to Travel and have lived and worked in The U.S the U.K and Australia. I hope to use my employment within A/V to work overseas in the future.
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