Spinning 3 phase motor backwards

[Mmfh]

Hey there,

Stupid question time again. I have a Rotary phase converter that has a 25hp idler motor, 3 phase of coarse. With the pony motor I have (starter motor) and the direction the pony motor turns, it spins the big brutus 25 hp idler the wrong direction according to the red arrow on the top of the motor.

What I'm wondering is, this motor has the fan inside the tail end, wondering if this motor is spinning the wrong direction would that mean the air from the fan is going the wrong direction? Instead of blowing through the motor its just blowing out the back. I can feel a lot of air coming out the tail end of it, not sure if this could get hot if run for a long time this way.

Did that make sense? The way I worded that? In order to spin the motor the other way I would need to replace the pony motor and funds are not available to do that right now.

Thanks very much!

Mm

 

[rlitman]

Is this a TEFC motor? A lot of those fans don't care about the direction of rotation.
Maybe a picture would help, but if the idler motor actually has a red arrow showing direction of rotation, that's a bit of a concern.

 

[Mmfh]

Yes it is a TEFC motor. I've seen a lot of motors with the arrow for direction sticker on them, this one points the opposite direction as what its turning now. I've also seen many places it says to change direction on any 3 phase motor just change two of the wires. Never heard anything about cooling not being effective turning the wrong way.

Its run awhile this way and has not caused any problems, just noticed this last night and thought I would bring it up.

Thanks

 

[Wastedwagesracing]

I have never seen a motor built that the fan did not work in either direction. I run lots of motors way down on the RPM range. On those applications I add an auxiliary 120 volt fan for added cooling.

 

[rlitman]

Yeah, swap 2 leads to reverse a 3 phase motor. That's the simple part.
I've never seen a 3 phase motor that couldn't be reversed either, but the arrow must have been put there for some purpose. Maybe it was re-purposed from some pump?

 

[Mmfh]

I bought this motor used many years ago, I'm sure it was used for something large, but I have no idea what.

That sticker with the arrow could just be for another application I guess?

 

[superdel]

Put your hand over the motor while it is running. The air should be blowing toward the shaft of the motor through the channels in the motor housing. Put your hand over the end bell. If there is a bit of suction, the fan is going the right way. If the air is blowing out of the end bell, away from the motor, it is going the wrong way. It should draw air in through the end bell and blow it over the motor. If it is going the wrong way, remove the end bell and take the fan off the shaft and turn it around facing the other way.

 

[Mmfh]

Put your hand over the motor while it is running. The air should be blowing toward the shaft of the motor through the channels in the motor housing. Put your hand over the end bell. If there is a bit of suction, the fan is going the right way. If the air is blowing out of the end bell, away from the motor, it is going the wrong way. It should draw air in through the end bell and blow it over the motor. If it is going the wrong way, remove the end bell and take the fan off the shaft and turn it around facing the other way.

I hadn't thought about turning the fan around, can it really be that easy? The way I envision the fan you won't be able to flip it, but I haven't been into a large motor in a lot of years.

I'll talk a look. Thank You!

 

[Tscott]

I'd be willing to bet the fan works fine in either direction. 3Ø motors are typically designed to run in either direction. This adds to the applications of the motor and reduces the number of parts manufacturers have to stock. I'd check it to be sure, but I'm thinking your good to go.

Tom

 

[pop pop]

All I've ever seen had a "radial" fan in that the fins ran from the shaft to the outer diameter. Won't matter which direction it's turning, just that it is turning.

 

[rlitman]

All I've ever seen had a "radial" fan in that the fins ran from the shaft to the outer diameter. Won't matter which direction it's turning, just that it is turning.

That's all I've seen under the hat in a TEFC motor too.

 

[Mmfh]

I'm probably good to go then. I felt a lot of air coming out of the fan end of the motor and not going through and out the front. Its probably fine and I'm concerned about nothing.

Thanks very much!

Mm

 

[Super Mech]

If it ain't broke don't fix it.

 

[Mmfh]

If it ain't broke don't fix it.

 

[PT Doc]

I'm probably good to go then. I felt a lot of air coming out of the fan end of the motor and not going through and out the front. Its probably fine and I'm concerned about nothing.

Thanks very much!

Mm

This seems like the exact opposite direction though. I would guess the fan could be reversed on the shaft. Likely a key/keyway setup. Use an ir temp gun on the motor when it's running to compare to some accepted standards for that type of motor.

 

[NWOhioChevyGuy]

Think of it this way, the fan is to cool the motor, as long as its drawing (or blowing) air across the motor it's doing what it needs to. Especially if your not pushing it to the extreme on power usage you are going to be fine either way.