2 Hp Or 3 Hp

[Kube]

Looking to replace a motor in my hot tub and was wondering if there really is a differenc between a 2 and 3 HP motor? I mean its the same revolutions per minute from the the same wetend? Also why does the 3 HP draw less AMP I would thing it would be larger. OR is it really just gimmick....The 3 HP motor with wetend is an identical fit were as the 2 HP is off by an inch so the 3 HP really would be easier to install since it would just be a swap.....its on a 2002 Marquis Hot Tub If that matters

[Mark]

The impeller of the pump wet end determines the load on the motor and therefore what the current rating of the motor needs to be to support the load. This is why it is critical to size the motor based upon the load of the impeller. If the rating of the motor is smaller then the impeller load, the motor will draw more current than what it was designed for and will burn out fairly quickly.

Also, label HP rating is only one of several factors which determine the rating of the motor. Service factor is also important but probably the most important rating is the maximum current or service factor current rating. This tells you how much current the motor can really draw. However, if you don't know what the motor will draw when put on a specific impeller, then the next best sizing method is with service factor HP (SFHP). SFHP = service factor * label HP. As long as the SFHP of the new motor is equal to or greater than the old motor, then you can be assured that it will be able to support the impeller load on the pump. So when comparing motors, use either the SFHP or the current ratings or even both but make sure the new motor equals or exceeds the rating of the old motor. Usually, if you have a motor part#, you can cross reference that with a manufacture's new motor number to make sure you get a match.

[Roger]

The impeller of the pump wet end determines the load on the motor and therefore what the current rating of the motor needs to be to support the load. This is why it is critical to size the motor based upon the load of the impeller. If the rating of the motor is smaller then the impeller load, the motor will draw more current than what it was designed for and will burn out fairly quickly.

Also, label HP rating is only one of several factors which determine the rating of the motor. Service factor is also important but probably the most important rating is the maximum current or service factor current rating. This tells you how much current the motor can really draw. However, if you don't know what the motor will draw when put on a specific impeller, then the next best sizing method is with service factor HP (SFHP). SFHP = service factor * label HP. As long as the SFHP of the new motor is equal to or greater than the old motor, then you can be assured that it will be able to support the impeller load on the pump. So when comparing motors, use either the SFHP or the current ratings or even both but make sure the new motor equals or exceeds the rating of the old motor. Usually, if you have a motor part#, you can cross reference that with a manufacture's new motor number to make sure you get a match.

That went over my head so fast I never even saw it!!!!

[Spa_Guru]

Amperage X voltage X 0.00134102209 = brake horsepower

The only way to get more HP with less amperage is to change from 120v to 240 v motors.

[Mark]

Don't forget the motor efficiency and power factor. The correct equation to go from input power to brake HP is:

Input Power (watts) = Volts (RMS) * Amps (RMS) * Power Factor

Brake HP = Input Power (watts) * Motor Efficiency / 745.7

OR

Brake HP = Volts (RMS) * Amps (RMS) * Power Factor * Motor Efficiency / 745.7