Member
Mike, when I mentioned coil impedance being a function of frequency, I was referring to the frequency of the rotor, not the incoming power. I can't remember the details, but it is the reason why locked rotor amperage is so high. I unfortunately did not retain my motors book from college (which I have deeply regretted over the years), so if you can find what I am talking about, you can re-educate me about it.Originally Posted by Mike Henderson
Member
Ricks on it.
The motor should do just fine at 50 Hz, just run a bit slower (about 16% slower)
The Hz is a function of frequency i.e. a function of time and if the alternating current changes 60 or 50 times per second it will only dictate the speed of rotation. As long as there is adequate potential or "voltage" to induce the field windings the motor will spin.
Contributor
50 Hz power is usually 380Y/220V, 400Y/230V, or 415Y/240V depending where you are in the world so one line to neutral is 220/230/240V and any 2 lines are 380-415V (The European Union has standardized it at 400/230V) BTW the color code for 230V is Blue = neutral, Brown = live/hot, Yellow w/ green stripe = Earth/ grounding conductor.
Contributor
That assumes there IS a second "line". I'm not sure how they set it up there, but it is possible to just tap the distribution transformer with a single secondary winding, and the voltage across that should be 240V. It doesn't necessarily have to be a single secondary winding with a center tap like we do in the US.
It sounds like the OP has access to two conductors which exhibit a potential of 240V between them, and the particulars of where those wires come from or where they are relative to ground is irrelevant.
The voltage difference of 220/230/240 is not significant, and shouldn't affect the motor in a noticable way. I actually discovered that I have 250Vrms in my shop...
+1 that the frequency difference won't matter, either. The motor will run fine, just slower.
Your only worry would be that the motor is now undersized (lower speed = lower HP), and/or that the motor will now get too hot. If you can't find a better solution (ie - an actual 50hz motor), I'd say give it a try, and just check the motor often to make sure it's not overheating.
Last edited by Dan Friedrichs; 05-13-2009 at 11:02 PM.
Contributor
Talk to Grizzly. Because they are a reseller, their supplier most likely has 50 HZ motors available. They don't just sell / build for Grizzly, but to other vendors in other countries. The 50 HZ motors could be direct shipped to you. As for your old 13" Rockwell, go over to OWWM's web site and test the waters for some one with a "parts machine" from whom you can get the needed parts. Exactly what parts are you looking for? Tell us the model and serial number. I know I have a 13" Rockwell, and a Delta 15", and there is no comparison between the machines. Delta may still have the parts you need to fix up the 13 incher. If not a machine shop could make the parts. Perhaps a technical school could do these as a live project. Global Tooling stocks knives to fit the 13" planer. Just some thoughts.
Contributor
VERY good point. I forgot about that. HP is a function of torque and RPM. If torque is the same but RPM decreases, the HP rating of the motor is decreased.
Thanks for pointing that out.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Member
Not true, If the potential is the same the HP remains. The Hz only effects frequency and thus the speed. It will have the same HP at 50 Hz as 60Hz just slower (~16% slower) ..and overheating should not be an issue unless it is way underpowered.
Contributor
Unless you can show that the torque increases by some percentage that offsets the lower speed, the HP will definitely decrease.
Look at 4 pole motors (1725 RPM) compared to 2 pole motors (3450 RPM) - the 4 pole motors are larger for the same HP.
Look at universal motors. They're quite small for the HP output because they run at very high RPMs (maybe 20,000 RPM).
RPM matters for HP (given the same torque).
A factory made 50Hz induction motor will be physically larger than a factory made 60Hz induction motor of the same HP because the 50Hz motor has to generate more torque compared to the 60Hz motor (for the same number of poles in each).
Around WWII, aircraft used 400Hz because it allowed lighter motors and generators.
Mike
[Go to Wikipedia and look up "Horsepower". Look down to "Electrical Horsepower/Relationship with torque".]
Last edited by Mike Henderson; 05-14-2009 at 1:51 AM.
Go into the world and do well. But more importantly, go into the world and do good.
Contributor
From my understanding a 50 HZ motor will fare better if operated on 60 HZ then a 60 HZ motor on 50HZ.
Contributor
Yep, the 50 Hz motor when operated at 60Hz will draw less current and will not overheat. And it will produce more than nameplate HP because it will have a higher RPM.
Mike
Last edited by Mike Henderson; 05-14-2009 at 1:18 AM.
Go into the world and do well. But more importantly, go into the world and do good.
Member
I stand corrected. A motor with 16% less rpm will have 16% less HP but will retain the torque as relative to the potential.
Member
Many people run 60 cycle synchronous motors on 50 cycle especially in third world countries. If you have near-correct voltage to allow the motor to run, it will run 5/6 as fast, not develop as much power, and over heat a bit. I would guess Nigeria's power is subject to all kinds of voltage sags, spikes and outages. So any motor - 50 cycle or 60 cycle - will not last as long in this environment.
Contributor
The issue with reduced frequency is that the CEMF is proportional to rotor speed.
If line voltage is maintained at design value, and the frequency reduced, stator current will rise dramatically.
Reduced speed also results in reduced power output, since torque is a fixed maximum, and speed is reduced, fan cooling of the motor is affected as well.
You can run a 3 phase motor at the correct volts/hertz value, which would be 5/6 of nameplate rating in this case. The only issue with reduced speed is that the Grizzly equipment is probably single phase? The motor speed would be reduced to 83% which may be getting close to the centrifugal starting switch rating.
Regards, Rod.
Last edited by Rod Sheridan; 05-14-2009 at 8:43 AM. Reason: Added single phase criteria
Contributor
Rod, I think the CEMF is proportional to the slip, rather than the rotor speed. The greater the slip, the greater the current induced in the rotor which increases the rotor magnetic field, which increases the CEMF in the stator.
The actual rotational speed of the rotor doesn't matter. Four (or more) pole motors rotate slower than a two pole motor but the mechanism of the CEMF works the same.
And to give credit where it's due, Rick C. mentioned this earlier.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Contributor
Hi Mike, my poor memory relates rotor current to slip, and CEMF to rotational speed.
I may well be wrong, it's been too many years since college, however if CEMF was related to slip, a VFD wouldn't have to reduce it's output voltage linearly with frequency, unless I'm missing something.....Regards, Rod.
Posting Permissions
Reply With Quote