This still has to do with your bicycle post, correct? You are missing something with trying to just run the motor slower without using gearing. Motor heat. A motor is made to run at a certain speed, and many are fan cooled, when you slow down a motor as much as you want to do, it will overheat. A motor that isn't fan cooled is also designed to run at a certain speed at a certain temperature and they will run excessively hot if not used at the correct speed too.

Even a 3phase motor on a VFD is limited on the amount under frequency it can be operated at.

An electric motor has it's highest power at 'locked rotor', but that has nothing to do with its real power, because it's not turning the shaft. The HP and output torque of an electric motor is measured at it's rated RPM. Running one slower than that will reduce both it's HP and output TQ. But it will use more electrical power, but just turn that power into heat. You need gearing to do what you want. Or a internal combustion motor, because they use a different way of making power and torque.

Hello, I had different results, I'm running a 5hp 240v motor on 120v just fine for my air compressor, was a 3400 rpm, i needed a 1500 speed to run my quincy pump, also I was thinking,,?, is any way to jump frequency down to match rotor speed , like 3,6,9,12 poles,? Cause doubled is same if fration iv down?

Mod: Created new thread, link to Old.
https://forum.allaboutcircuits.com/...e-keeping-torque-the-same.147976/post-1262458

 

Hello, I had different results, I'm running a 5hp 240v motor on 120v just fine for my air compressor, was a 3400 rpm, i needed a 1500 speed to run my quincy pump, also I was thinking,,?, is any way to jump frequency down to match rotor speed , like 3,6,9,12 poles,? Cause doubled is same if fration iv down?

Look at the date of that message you are responding to.

 

Hello, I had different results, I'm running a 5hp 240v motor on 120v just fine for my air compressor, was a 3400 rpm, i needed a 1500 speed to run my quincy pump, also I was thinking,,?, is any way to jump frequency down to match rotor speed , like 3,6,9,12 poles,? Cause doubled is same if fration iv down?

Hello,

Wow 5hp for an air compressor.

Sometimes motors can run better with a different frequency and then a VFD (Variable Frequency Drive) is used to run them. The VFD can be expensive though.

[Note: This reply was to a reply to a much older thread and a new thread was created.]

 

Much better off with a pulley size change,.