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Selected as the "Favorite Place to Purchase a Vacuum"
In August, 2009 the readers of Lancaster Newspapers again voted Ristenbatt
Vacuum as the "Favorite Place to Purchase a Vacuum."
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Suction Motor Design & Operation
The suction motor is one of the most important parts of a
vacuum cleaner. It is this motor which takes the electrical power from
the power source and converts it into mechanical power in the form of
suction with
air flow. Rating the motor for its ability
to produce suction with air flow is one of the most misrepresented and
misunderstood aspects of vacuum cleaner technology. This confusion has been
accentuated by many manufacturers in their attempt to make their
products appear superior to others. Various methods of rating the
suction motor's performance are discussed in the article on the
Power of the Suction Motor. This article will
focus more on the physical aspects and attributes of the suction motor.
Some technical terms associated with the suction motor include universal, series and brush type. All suction motors, except for the very
small battery operated motors, are universal type motors since they can
operate with either AC (alternating current) or DC (direct current) power
sources. Typically they are designed for best performance with AC at the
normal household voltage.
This type of motor consists of a rotating
armature and a stationary
field. The armature is made of a laminated
iron core which is wound with copper enamel-insulated wire. The windings
are attached to a copper commutator near one end of the armature. The
commutator has individual bars of copper which are positioned in the shape
of a drum. The motor brushes are carbon rods
which are held against the commutator in order to carry the electrical
current to the windings on the armature.
The field consists of a laminated iron frame on which one or two coils
of copper wire are wound. It is shaped so that it wraps around the core
of the armature on two opposite sides. Since the same current passes
through the field coils and the armature coils, it is termed a series
motor. As current passes through the coils in the field and armature,
magnetic fields are created by each of them.
It is the attracting or repelling of these fields which cause the armature
to rotate within the field. The fan
is often considered an integral part of the suction motor since it, the
fan housings and the motor are assembled as a unit by the manufacturer. Being a series type motor it is capable of creating high levels of
torque for its size. You will find series
type motors commonly used in electric shavers, food mixers, electric drills
and other portable electric power tools. As current increases through
the motor, the magnetic fields created by both the armature and field
increase proportionally. Therefore, with lighter
loads, the torque is proportional to the
square of the amount of current flowing through the motor. If the current
is doubled, the torque is increased by four times. Under heavy loads the
field's magnetic strength reaches a point of saturation whereby it can no
longer increase. Then the torque increases only in proportion with the
change in the current flow. Suction motors are designed to operate at
very high speeds under moderate to heavy loads.
The load to the suction motor is an interesting
and unusual phonomania. One or more fans are attached to the motor shaft
and are rotated at a very high speed. The air entering the fan near the
hub is forced to spin with the fan as it passes through it. The load to
the motor is the force needed to overcome the
inertia of the air as it enters the fan and
is spun. When you reduce the air flow through the motor by increasing the
resistance to the air flow, the load on the
motor is actually reduced so the motor speed increases and
amperage through it decreases. The effect
of this is to increase the suction created by the motor which helps to
counteract the effect of the resistance to the air flow. If you restrict
the air flow completely, it will create its maximum possible suction.
This happens when a sealed suction gauge is
used. In essence, it is greater than the suction which is produced in the
normal operating range of the motor.
Suction motors on most vacuum cleaners typically draw seven
to twelve
amperes (amps) of current from the
electrical power source. (Twelve amps is the maximum permitted for
any appliance which plugs into a standard household electrical outlet.
If you see a rating larger than twelve on a vacuum cleaner, it is
probably an Cleaning Performance Rating,
not amps!) A substantial amount of energy is dissipated in the form of heat. This is primarily the result of resistance in the copper windings on the
armature and field as current flows through them. Vacuum cleaners, like
traditional uprights, which do not remove
the dirt from the air before it passes through the fan use what is known as
a bypass cooled motor. A separate fan
circulates clean air around the armature and field to cool them. This
design is also used on almost all commercial tank and wet/dry vacuum
cleaners since it is unsafe to pass damp or wet air over the electrical
components. Most household canisters
(and power teams) and
clean-air system uprights use a
flow-thru cooling design. Since the air
reaching the fans is already quite clean in these systems, it is directed
around the armature and field to cool them after it exits the fans. This
makes for a typically quieter operation. Since the motor could overheat
if the air flow is greatly or completely restricted, a means is often
provided to either stop the motor at a preset temperature or open a safety
valve to allow for extra air flow to cool the motor.
PageType: Educational
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