A fractional horsepower motor is a motor built in a frame and has power rating smaller than one horsepower. Also known as FHP motors, being categorized as a fractional hp motor can be relative to the frame size as well as the amount of fractional horsepower. For instance, if the frame size is a 42, 48 or 56, the motor can still be classified as a fractional horsepower motor even if the horsepower exceeds one horsepower, although motors such as ½ HP motors and ¼ HP motors are more easily identifiable.
The frame size of fractional horsepower motors is based on the standards put in place by the National Electrical Manufacturers Association (NEMA), and at times, fractional horsepower motors can be referred to as NEMA motors. Despite being relatively small motors, at times even called miniature motors depending on the frame size, fractional horsepower motors are widely used for controlled motion in industries including: medical, for surgical devices in hospitals; automotive, for many applications such as electric windows, powered seats, central locking systems and more; residential, for household appliances such as washing machines and refrigerators; industrial manufacturing, in pumps, compressors and many other necessary components and processing and assembly applications; and HVAC, for the operation of equipment such as fans and blowers.
Fractional horsepower motors can come in a wide variety of types and can be fuel powered, although they are most often electric. Thus, most often seen as small electric motors, fractional horsepower motors can fulfill many functions as universal motors, variable speed motors and even reversible motors. As a universal electric motor, fractional horsepower motors are capable of functioning on either direct current (DC), in which the current flows in one direction or alternating current (AC), in which the current that flows in either direction. As variable speed motors, fractional horsepower motors are able to direct the rotational speed of an AC or DC motor, causing it to slow down or speed up as desired. Fractional horsepower motors are a popular type of variable speed motor because the smaller horsepower allows for easier control of motion and speed. As a reversible motor, fractional horsepower motors function to reverse the direction of rotation by way of a switch that controls the motor connections when the motor is inactive. Much like a variable speed FHP motor, reversible FHP motors work well because of the increased precision in control. Besides fuel and electrical power, fractional horse power motors can also be powered by means of permanent magnets, which are referred to as permanent magnet motors.
The basic design of an electric powered fractional horsepower motor consists of an enclosure, rotor, axle, coil and field magnet. Some contain brushes, which are used to help conduct the electrical currents. If the motor is brushless, then an external power supply must be used to transfer the current. Because of their lack of brushes, brushless electric motors are actually more expensive. Although they can be AC or DC, both types of electric fractional horsepower motors use magnets to provide the motion necessary for power generation. The magnets provide motion by reacting with the electrical current, which causes rotation by flowing through specific points of the motor. The rotational movement provides power that can then be transferred into the desired equipment. In order for an electric motor to be classified as a fractional horsepower motor, it must have a rated output power of 746 watts or less. A watt is a unit of measurement equal to one joule per second. The design of a fuel-powered fractional horsepower motor is similar, except instead of the coil and field magnet, a fuel-powered motor will feature exhaust valves and a fuel chamber. Commonly referred to as internal combustion engines, fuel-powered FHP motors may use either gasoline (called petrol in Britain) or diesel, although each type calls for a slightly different design.
Fractional horsepower motors are becoming increasingly popular in many industrial, residential and commercial applications. The technology for electric motors was first developed by Nicola Tesla in 1888, the year he patented his induction motor. However, it was when cities began to have electricity in 1915 that the fractional horsepower motor industry began to rapidly develop. In fact, fractional horsepower motors experienced their first big push in popularity in the 1920s due to the invention and eventual wide-spread use of appliance such as power washers. However, fractional horsepower motors began to truly become highly popular after World War II with the rise in consumerism experienced during the 1950s and 60s. Ever since, and particularly in the early 2000s, the market for fractional horsepower motors has steadily grown, showing no signs of slowing down due to their environmentally-friendly levels of power generation efficiency. Most notably, fractional horsepower motors have become widely used for applications such as automotive systems, household appliances and power tools. Often needing to be customized for more unique applications, the essential elements of a fractional horsepower motor that need to be kept in mind are the voltage, frequency and number of phases of power supply needed.
Fractional Horsepower Motors Types
- 1/2 HP motor are fractional horsepower motors with a power output of ½ HP, which is roughly equivalent to 373 Watts.
- 1/4 HP motor are fractional horsepower motors because they output power that is less
than one HP, or 746 watts when referring to electric motors.
are either induction or synchronous. They have a
current that flows in either direction, usually with electric power.
- have variable speed operation capabilities with current,
which flows in one direction. Often use electric power.
are motors that convert electric energy into motion using magnetism.
- FHP motors is the abbreviation for fractional horsepower motors, which are motors
that are built in a frame, traditionally with a power output of smaller
than one horsepower.
a combination of a motor and gearhead that reduce motor speed to desired
- are used when minimum speed variation requirements
are necessary at constant potential with full to no load and/or constant
- Miniature motors also referred to as micro motors or small motors,
are fractional horsepower motors that must not only fit the frame size
and/or less than one horsepower requirements, but also size dimensions
of a couple inches or less.
come in two, three or four speeds. They have varying connections
that can alter the speed at the starter, because of the way they are
- NEMA motors are electric motors that fit the standards set by NEMA, which stands for the National Electrical Manufacturers Association.
have magnets in their rotor assemblies. These
allow the rotor assembly to arrange itself in a line with the rotating
field of the stator, which results in no slip and higher torque efficiency.
- Reversible motors can be AC or DC. A typical DC motor is almost always reversible
by changing the polarity of the field; an AC motor is reversed in a
three-phase power motor by reversing connections of one leg and in a
single phase by reversing the leads.
- have less than one horsepower of power.
- Small motors use a fraction of a horsepower, or 745.7 watts, of power to run.
operate up to full load at a constant speed and are often used to maintain
an exact speed. The rotor speed and the rotating magnetic field speed
- can run on either AC or DC power.
- are capable of operating on both direct current and alternating current.
- direct the rotational speed of an AC motor and can be found in many heating and cooling systems.
are essentially multi-speed motors whose loads
have varying torque requirements along with varying speed requirements.
Found in pumps and blowers.
Fractional Horsepower Motors Terms
A device that creates mechanical motion by converting various forms of
energy to rotating or linear mechanical energy.
Electrical conductors in the core slot, insulated from the iron core.
They produce and transmit the magnetic field as current passes through.
- A mounted cylindrical
device, to which the motor brushes are attached, on the armature shaft
made of copper segments set around the shaft.
- Name used for
motors with variables speeds whose loads need the same amount of horsepower
despite their speed.
- The segment of the stator
and rotor, usually iron; made up of cylindrical laminated electric steel.
A complete reverse flow of alternating current during a rate of time.
- The comparison
of operating and rest times due to normal operating temperature.
The ratio of electrical input to mechanical output. It measures the motor's
effectiveness when converting electrical energy into mechanical energy.
- Either open or
closed, the frame or housing of the motor.
- The part of the
motor housing that supports the bearing and acts as a protective guard
to the electrical and rotating parts inside the motor. An endshield is
often referred to as an "end bracket" or "end bell."
- Work done
per unit of time: 1 horsepower equals 33,000 foot-pounds of work per minute
or approximately 746 watts. Motors for pumps are an example of a motor
that is rated in horsepower.
- A device used for
the positioning of a motor. These are adjustable screws fitted on the
base or motor frame.
- The burden of the motor
by its application. The required power to overcome the resistance of the
machine it powers.
- A device that turns
a shaft by taking electrical energy and converting it into mechanical
- Made of stacked laminations,
the rotating component of an induction motor.
- The rotating part of
the motor that protrudes past the bearings for attachment to the driven
- The laminations arranged
on a rotor or armature. These help abolish low-speed cogging effects in
an armature and reduce induced vibration in a rotor.
- In an AC induction
motor, it is made of laminations with a large hole in the center for the
rotor to turn and slots in the stator for the windings to be inserted.
- A device to detect
temperature that contains two dissimilar metals which generate voltage
as a function of temperature.