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3phase induction motors

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lilshawn:

--- Quote from: jennifer on November 23, 2012, 07:50:16 pm ---     Im so going to cry myself to sleep, Omg.... That is quite a rash of information, And again I understand most of it,

--- End quote ---

don't worry, you needn't worry much about it.


--- Quote from: jennifer on November 23, 2012, 07:50:16 pm --- So Basically a smaller
motor would use less energy and consequently doing less work, In the design of a booth, or pump station, all these factors would have to be
taken into account to make it efficient... If say a 1/8 hp motor was used, in the same set-up, besides being underpowered, would have to
work harder to spin the same load to its rated point then stabilize to a less torque situation....

--- End quote ---

yes, exactly. your going to hit a wall where you can't move any more air with the fan/or the room will not accept any more. ideally you want them to be the same.


--- Quote from: jennifer on November 23, 2012, 07:50:16 pm --- I can see from an engineering standpoint where
in the design the ratings of the motor were taken into account, not just upgraded until it worked... This is a whole different concept than
say, building a cab, Where the power needed is determined by its load, not the amount of work... Whoever thought to rate BHP, was
pretty much on the cutting edge for the day, Jennifer may look into that a little, just to satisfy my curiosity (Not to build a steam powered spray booth).

--- End quote ---

good thing we aren't engineers, otherwise you'd really be lost XD

MonMotha:

--- Quote from: lilshawn on November 24, 2012, 03:56:13 pm ---good thing we aren't engineers, otherwise you'd really be lost XD

--- End quote ---
Speak for yourself...

I guess that may explain why I confuse people so frequently :)


--- Quote from: jennifer on November 23, 2012, 07:50:16 pm ---Where the power needed is determined by its load, not the amount of work.

--- End quote ---
A key thing to realize is that power is just work over time.  You may be doing work to create heat, light, move air, turn a conveyor belt, etc., but it's just work over time.  The concepts are interchangeable, but it's sometimes convenient to think of things in one or the other.  e.g. when you want to know how much power you need to move a certain volume of air, you can work out the rotational speed an torque required on the fan blade to get the mechanical power.  Then if you want to also plug your arcade cabinet in to that circuit, you can just add the powers up, not caring about how the "work" gets done inside the cabinet.

You also cannot rely on an induction motor to power limit itself by slowing down in a fan application.  An induction motor will want to run close to (but shy of) the synchronous line frequency regardless of how much torque it has to develop to do that.  If it has to develop more torque than rated, thus exceeding its rated power, to attain that speed, it will draw more current than it's designed for and burn out.  In this case, your only options are:
1) Use a different fan blade that requires less power to turn at that speed (and therefore probably moves less air)
2) Slow down the motor e.g. using a VFD (moving less air)
3) Use a bigger motor that's rated for more power (and therefore it draws more power)

Note that this is somewhat different than the high speed "universal" motors commonly found in e.g. vacuum cleaners.  These will, to some degree, power limit themselves by adjusting their speed based on torque requirements.

DaOld Man:
I think Jennifer should forget this silly induction motor idea and hire Geisha girls with paddle fans.
Why back in my day you could hire them for peanuts, and most of them aint too hard on the eyes either.

(Ok DaOld Man will go back to sleep now.)

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