HVAC Motor Types (RSES NATE Prep)
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- เผยแพร่เมื่อ 22 ก.พ. 2020
- In our new series, Bryan uses some resources from RSES NATE Prep to do some quick videos full of useful HVAC tips and data. In the first installment, Bryan discusses HVAC motor types.
One of the first major motor types is the shaded pole motor. This motor supplies low torque and is generally used in applications below 35 watts. You can typically see the stator extending from the motor. They tend to be low-efficiency motors for small appliances and don't require a capacitor because the shading ring assists with the startup. These motors can only rotate in one direction.
Split-phase motors are a common category of residential HVAC motors. These motors are used in applications that use split-phase power from a center-tapped transformer. They have medium starting torque and create a phase shift from high resistance on the start winding; a centrifugal switch could take the start winding out of the circuit. Otherwise, capacitors may be used to provide a phase switch.
Compressors are also motors; they are the largest motors in the system and may come in open-drive, semi-hermetic, or hermetic compressors. The latter two types have motors inside the compressor in the refrigerant circuit, and open-drive compressors have motors external to the refrigerant circuit. Compressors may be cooled by suction gas; otherwise, hermetic and semi-hermetic compressors may experience burnout if they overheat or experience arcing, which can contaminate the system. Nowadays, we have variable-speed or multi-stage compressors to match the load to the capacity more easily. Compressors should also NEVER be run into a deep vacuum.
Compressors and motors have ratings, including the RLA (rated load amps) and MCC (maximum continuous current). MCC refers to the maximum amount of current that won't trip the overload, whereas RLA represents what we would expect during normal operation; the RLA can be determined by taking the MCC and dividing it by 1.6.
A compressor may have a permanent split capacitor (PSC) motor, which is a single-phase motor that connects to a run capacitor between the start and run windings. The current that moves in and out of the start winding is dictated by the run capacitor; the capacitance restricts the current based on the capacitor's microfarad rating.
On the other hand, capacitor start capacitor run (CSCR) motors use both start and run capacitors. A relay takes the start capacitor out of the circuit when the motor gets up to speed, but the run capacitor stays in the circuit.
ECMs are electrically commutated motors, which have permanent magnet rotors and are controlled by a brushless DC motor. These motors are common on blowers and have a wide operating envelope for superior humidity control, efficiency, and operating temperatures.
Motor speed is determined by synchronous speed and slippage. The synchronous speed is the speed at which the magnet rotates (and is determined by the number of poles), and slippage is the difference between the synchronous speed and the actual speed.
Visit the RSES website here: www.rses.org/
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/
As always, great stuff guys. Thanks.
Before the internet, RSES was about our only source of quality HVAC/R information and training.
Never too old to pick up info. Thanks. Learned something I knew but not why.
Outstanding teacher and communicator !
Great video. Thank you for all your contributions to the industry.
I like those videos, I am not only studying refrigeration, but also English.
Thanks Bryan
Great content Bryan! I like the books and PowerPoint slides that RSES has produced. I used a lot of their material when teaching NATE prep courses at a local technical colleges. Everything from the content to the layout of the material makes it very easy to use.
Great stuff
Thank you sooo much for teaching us today man we really appreciate you it made so much sence THANK YOU
Ezequiel Crespo thanks brother 👍🏻
Excellent video! Info it's really helpful. Saludos desde cordoba Argentina
Thank you again
Wow 😱👏👏Great stuff right here.. Where was i all this while.. Anyway Thanks Man😉👍
Thanks!
For those that find themselves stopping the video and replaying to try and catch all that is said, you might want to adjust the playback speed down to .75 after the 8:00 minute mark.
Really appreciate the video thank you, subbed
Just after 2:35 you mentioned that residential pole transformers have windings that are wrapped in opposite directions. I scratched my head about that one. Opposite wrapping would make the leg to leg 240V option unusable. I'm guessing you're describing how these are manufactured, from the perspective of a neutral pole at one end. A long center tap wire could be vulnerable to overheating and it might mess up the magnetic field strength and cause harmonics. So they move the center tap to one end and wind the two coil ends both downward from the neutral at one end. If you do that you need to reverse direction to give the two coils opposite polarity. Just like a screw, or like inverting a glove, the 'opposite winding' is a curious mirror image viewpoint from the middle tap. Interesting, I did not know that.
shaded pole motors rotation can be reversed by disassembling the motor and turning the stator over! You are in correct, they can change direction.
When needing to replace a motor is replacing one with the same amps crucial or is hp and rpm all that matters?
Great video, but error at 5: 38, change semi hermetic to hermetic. I’ll be using this for my student!
I was expecting ECM blower motors to be VFD inverter driven three phase induction motors.
Permanent magnet motors, or at least ones with good quality magnets, require rare earth metals that cost more. Example of poor permanent magnet motor is auto electric windows that become weak over time because of cheap metals used for magnets that become weak magnets with use.
Induction motor's rotor 'slip' is necessary to have a relative magnetic field rotation between stator and rotor to 'induce' current into rotor. The amount of slip speed delta varies typically between 1-8% lower than synchronous speed based on mechanical load on motor.
Generally, optimum run capacitor value creates a 90-degree current difference between run and start windings of single-phase induction motor. It also improves motor's run AC load power factor. Same applies for start capacitor, but because motor winding inductance is so much lower during start up time, the start capacitor must be much greater capacitance than run capacitor. Start caps are typically the black plastic cased capacitor and are made with an electrolyte to achieve more capacitance for its physical size. Start caps have higher internal resistance so cannot be energized for a long period of time or they will overheat and self-destruct. Start capacitors are generally less reliable than foil run capacitors due to the electrolyte drying out over time.
AC load power factor on induction motors varies with mechanical load, getting worse as mechanical loading is less.
Often, single phase induction motors start and run windings are made with different wire gauge and/or different number of turns (as indicated by their winding resistance difference) so it is not a good idea to swap run and start connections to make a single-phase induction motor run in reverse.
how does a multi-horsepower motor wired inside of the motor? Thanks
Wish I could get into HVAC to bad it's too late.
Brian are you in the field? I would hate to see the hourly rate to have your knowledge on a call!!
He owns his own company, Kalos in florida
loves to hear himself talk .... no real data
This video needs to be taken down and have the errors fixed and re-uploaded. The errors aren't constantly popping up but there are more than enough that it needs to be addressed. Gotta thoroughly proof watch an educational video before you release it into the wild.
You have a lot of knowledge but talk way too fast, please slow down