Hi, I'm Vance and welcome to Spec. Sense.
Fractional horsepower motors are a versatile workhorse used in appliances, furnaces, commercial
HVAC equipment and pumps.
When sized correctly most motors can last for decades,
but overheating, moisture and mechanical stress might cause a motor to fail earlier.
The motor nameplate is the key for finding a replacement as it lists the model number
and electrical specs of the motor.
In some cases the model number can be used to find an OEM motor or a direct cross reference.
If needed you can still use the motor specifications to find a proper replacement.
First match the physical specs.
This includes the motor diameter, shaft size, and mounting type.
Then match the electrical specs.
Which includes Horsepower, Voltage, Amps, RPM, rotation, motor type and capacitor size.
Mismatching will reduce motor life and performance so It's important to find the right replacement.
An overloaded motor draws more amps, runs hot, and will be slower.
An underloaded motor will also overheat and be highly inefficient.
In this episode, we'll take a closer look at each of these specs.
First measure diameter and length of the motor.
Next note the shaft diameter, and length.
Smaller motors will generally have a C-frame, a 3.3 inch frame, or a 4.4 inch frame .
Motors larger than 5 inches in diameter, will use the standard frame sizes 42, 48 and 56.
Now check the mounting type. This could be a ridgid base, belly band, or a stud mount.
Belt Drive Motors will use a rigid base.
On the other hand, direct drive motors will likely use a belly band.
Now that you've narrowed down a motor of the same physical size,
it's time to match the electrical specs.
The motor horsepower refers to how much work the motor can
produce at its rated voltage and speed.
For example furnace blower motors are generally 1/8 horsepower or more.
Small utility fans are around 1/15 horsepower or less.
Next note the voltage rating.
This is the optimal performing voltage of the motor, with a 10% tolerance for fluctuations.
Dual voltage motors, such as those rated for both 115 and 230 volts,
can be wired and operated at either voltage.
The current rating, or full load amps, describes the current draw
when the motor is operating at its full load.
The current will be different based on the horsepower, motor type and overall efficiency.
Keep in mind that not all motors of the same horsepower will function the same,
so it is still best to try to match both horsepower and amperage.
Next look at the motor speed and the number of speeds.
Synchronous motor speed is the speed of the rotating magnetic field and is determined
by the number of poles.
The rated motor speed will be lower then the synchronous speed.
For example a 4 pole 1800 rpm motor will likely have a rated speed of around 1700.
And a 6 pole 1200 rpm motor will be around 1100.
this is because all induction motors slip a little when under full load.
Slip is basically a magnetic field offset between the windings and rotor that causes
the motor shaft to rotate and generate torque.
Torque increases as slip increases.
To further decrease the speed, some motors will use several wire taps, each with more
resistance, which increases the amount of slip.
These are multi-speed motors and will often have multiple speeds and amp ratings listed.
If there is only one speed and one amp rating listed, then it will be for the highest speed.
The direction of rotation is usually written as a code.
The code describes whether the motor rotates clockwise or counter clockwise defined from
either the shaft end, or from the lead end.
Now these are opposites. So clockwise lead end (CWLE) is equivalent to counter clockwise shaft end (CCWSE).
Now keep in mind some motors are reversible, and will have a diagram on the nameplate
showing how to wire for each direction.
PSC and Shaded Pole Motors are the most common motor type used in HVAC applications.
A PSC motor can be used to replace a shaded pole motor, but not the other way around.
For the same horsepower, RPM and speed, shaded pole motors will draw twice the amps
since they are half as efficient as a PSC motor.
Therefore, using a shaded pole motor to replace a PSC Motor is not recommended.
These motors will draw more amps, and might cause the breaker to trip.
When replacing a defective motor It's also recommended to replace the capacitor.
Capacitors are an energy storage device that provide the proper magnetic phase angle
and torque needed for rotation.
This will either be a Start Capacitor in a Capacitor Start motor
or a Run Capacitor in a PSC motor.
The capacitance, expressed in microfarads, is a rating of how much energy that can be
stored in the capacitor.
This should be matched exactly.
The voltage rating refers to the maximum voltage that the capacitor can be exposed to.
You can use a capacitor with a equal or higher voltage rating but never with a lower rating
as this can result in capacitor failure.
Dual run Capacitors are used to support two electric motors.
Like in air conditioners that use both a compressor and blower fan.
They will have two microfarad ratings.
The higher rating is usually for the compressor, and the lower rating is for the fan.
Another important factor is to consider the enclosure type.
This is determined by the motor application.
Most HVAC motors will be air over motors,
and will use the air it moves to cool the motor as it runs.
A lot of these motors are rated for continuous duty.
Larger motors are designed to be cooled by more airflow, so putting a large motor in
low airflow system will cause heating issues.
Air over motors come in 2 variations.
Open Air Over Motors (OAO) have a vented housing and are used in clean dry areas,
like in furnace blowers.
Totally enclosed air over motors (TEAO) are used in outdoor or harsh environments,
like in air conditioner condensers.
Open drip-proof motors (ODP) have vents in the bottom of the housing for passive cooling,
and will offer some protection from dripping water.
Totally enclosed Non ventilated motors (TENV) are used in dusty areas and are cooled passively.
Hopefully this video has given you a better understanding of motors
and how to find a replacement.
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And if you need help, you can call or visit an AMRE location
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Thanks for watching.