Dual HP Rated Motor

[wvengineer]

I'm trying to select the heaters for this motor. I'm now second guessing myself. This motor has what appears to be dual HP ratings just based on slip??? Why wouldn't it just have the higher HP rating if it was OK to run it at that load? This is on an axial fan. It also appears to me that the LRA code changes which doesn't make any sense to me either. Anyone seen this before?

 

[ptonsparky]

Size everything for the higher horsepower. This is very common on grain drying equipment and I believe has to do with the static pressure while operating. Different grains will have different air flow. Someone here knows more.

 

[Jraef]

It's a special fan duty motor and the different slip values have to do with the type of fan connected to it. Direct drive in-line axial fan (probably yours) means there is no mechanical advantage of belts and pulleys, so the slip will be higher (slower speed), it puts out more torque and draws more current, hence the odd 19.4HP rating. But because the motor is IN the air flow, the motor can withstand this extra loading without exceeding the rated operating temperature. If the motor is used on a belt driven fan or blower (or some other machine) and is not in the air stream, then it's just the 15HP rating, normal slip.

This is very similar to having a "1.3 Service Factor", but they purposely don't show it that way (note the SF=1.0) because it can ONLY be used at the higher value IF it is mounted in the air stream on an axial fan. If they just put "SF = 1.30", someone would assume they can use it on a belt driven application without the motor being in the air stream and the motor would burn up.

 

[kwired]

It's a special fan duty motor and the different slip values have to do with the type of fan connected to it. Direct drive in-line axial fan (probably yours) means there is no mechanical advantage of belts and pulleys, so the slip will be higher (slower speed), it puts out more torque and draws more current, hence the odd 19.4HP rating. But because the motor is IN the air flow, the motor can withstand this extra loading without exceeding the rated operating temperature. If the motor is used on a belt driven fan or blower (or some other machine) and is not in the air stream, then it's just the 15HP rating, normal slip.

This is very similar to having a "1.3 Service Factor", but they purposely don't show it that way (note the SF=1.0) because it can ONLY be used at the higher value IF it is mounted in the air stream on an axial fan. If they just put "SF = 1.30", someone would assume they can use it on a belt driven application without the motor being in the air stream and the motor would burn up.

Never seen such a fan on grain equipment that was belt driven, but what you say does make sense if it were to be done that way.

OP needs to set overload according to whatever condition applies to him.

 

[Russs57]

Next to the rivet on the right.....the last column.....I can't quite make it out.

It looks like FPM, as in feet per minute. Could it be that the motor is rated for 15 HP at 900 FPM but rated for 19.4 HP at 4,000 FPM?

You could still have a motor in the air stream with a belt drive package.