Can A 50 Hz Motor Be Run On 60 Hz?

[David S]

I think 746..just a typo

David

 

[John Hasler]

I think that motors are rated at some fairly high load, perhaps full rated load.

As far as I know NEMA motors are rated at full load, which is the load at which they can run continuously.

Well, quality industrial rated domestically built motors anyway. Cheap motors are rated using some Hocus Pocus method that makes them more than 100% efficient. I have two 115v shop vacs with 15 amp plugs that both claim 5.5hp. Sorry, that is impossible, unless smoke and mirrors are involved...

I think that is the peak power that the motor can put out for a few seconds. A totally useless number, of course.

 

[JimDawson]

As far as I know NEMA motors are rated at full load, which is the load at which they can run continuously. I think that is the peak power that the motor can put out for a few seconds. A totally useless number, of course.

I think that number is something just dreamed up by the marketing department. But most marketing types live in an alternate universe where our laws of physics don't apply.

 

[John Hasler]

I think that number is something just dreamed up by the marketing department. But most marketing types live in an alternate universe where our laws of physics don't apply.

Oh, I suspect that you can get 5.5hp out of that motor for a few seconds. It is a series motor, after all. Run it up to max rpm no load, pop the clutch to the dynamometer, and watch the needle briefly touch 5.5hp. Then the motor catches fire and the breaker trips.

[Edit] Also, to the people who sell these sorts of products rating of a motor is the power *input*. On those machines all the air goes through the motor so it can be quite the hair dryer without melting.

 

[Bob Korves]

Oh, I suspect that you can get 5.5hp out of that motor for a few seconds. It is a series motor, after all. Run it up to max rpm no load, pop the clutch to the dynamometer, and watch the needle briefly touch 5.5hp. Then the motor catches fire and the breaker trips.

[Edit] Also, to the people who sell these sorts of products rating of a motor is the power *input*. On those machines all the air goes through the motor so it can be quite the hair dryer without melting.

Well, it can't really be input, either. 5.5 hp times 746 watts per hp divided by 115 v equals 35.7 amps. The 115v supply will trip long before that. Marketing hype and not being held accountable are no doubt the main reasons.

 

[John Hasler]

Well, it can't really be input, either. 5.5 hp times 746 watts per hp divided by 115 v equals 35.7 amps. The 115v supply will trip long before that. Marketing hype and not being held accountable are no doubt the main reasons.

The rated current of a circuit breaker is the current that it will carry without ever tripping. It won't trip instantly above that: you'd never start a motor. There is a time delay that decreases as the overcurrent increases. The instant trip current can be many times the rated current.

http://static.schneider-electric.us...100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf

 

[Bob Korves]

The rated current of a circuit breaker is the current that it will carry without ever tripping. It won't trip instantly above that: you'd never start a motor. There is a time delay that decreases as the overcurrent increases. The instant trip current can be many times the rated current.

http://static.schneider-electric.us/docs/Circuit Protection/Molded Case Circuit Breakers/0100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf

I see, John. Thanks. The break times listed in your link are much longer than I anticipated at overload. Of course, even giving a rating that a motor might sustain for a minute or so until the breaker opens or the motor or wiring melts is not at all being honest with the customer. There was a time when ratings were conservative, and a motor would be rated at a value that it could sustain indefinitely, and with a generous reserve for less than perfect conditions. Some are still rated with that mindset, and have good reputations.

 

[John Hasler]

I see, John. Thanks. The break times listed in your link are much longer than I anticipated at overload. Of course, even giving a rating that a motor might sustain for a minute or so until the breaker opens or the motor or wiring melts is not at all being honest with the customer. There was a time when ratings were conservative, and a motor would be rated at a value that it could sustain indefinitely, and with a generous reserve for less than perfect conditions. Some are still rated with that mindset, and have good reputations.

I agree that the 5.5hp rating is ridiculous but on the other hand continuous-duty ratings for many applications would not be very useful. You don't really want to know how much power your electric drill could reliably deliver running 24 hours a day. You want to know what peak power it can deliver for long enough to drill a hole.

 

[mzayd3]

It will be fine so long as the volt : hertz ratio is consistent. Otherwise, motor life might shortened a little bit. It should be fine.


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[4GSR]

Remember all of the old Craftsman power tools that were rated at peak horse power? Some more smoke & mirrors tricks Sears marketing used.