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3phase induction motors
DaOld Man:
Those are going to cost the baby.
Jennifer, cant you just use a single phase motor for the fan? Single phase speed controllers are a lot cheaper than smart VFD single to 3 phase converters.
jennifer:
Option this, ratings that, So confused...The Rpm formulas do seem to be a part of the overall picture, Even with a simple fan.
The faster the fan turns the harder it has to work, Tourqe than becomes issue...OMG... This isnt as simple as I first thought.
The Soft start of the 3phse and the variable control is kinda what Im thinking here, even though there may be cheaper options.
After looking (and getting lost navigating the site) This Bardac VFD co. seems to have what I need.
lilshawn:
--- Quote from: jennifer on November 20, 2012, 09:48:46 pm ---Even with a simple fan. The faster the fan turns the harder it has to work, Torque than becomes issue
--- End quote ---
not necessarily true though. motors are funny things. you'd think it would be a straight line...faster speed means more torque and more power needed. But in reality its more of a logarithmic curve shape.
(orange line) a huge surge of power is required to start the motor turning but as your speed increases, the power required to maintain that speed drops significantly. this is because the motor has rotational inertia that wants to keep going. it's easier to keep something moving.
BUT it changes again once you put a static load on it (like a fan blade)
the load (PINK LINE) will start out high but stay higher throughout the rpm range. much like you'd expect... it takes more power to achieve the same RPM, but it doesn't really vary much. with it's lowest power consumption right at it's rated and designed RPM speed.
also i messed up my labels on the graph... up and down should be power and left to right should be time. oops.
jennifer:
Oddly enough I understand what your saying.... Your graph is Awsome and pleases me, Unfortunally this creates a problem,
You guys (all of you) seem quite knowledgeable on this subject and I will treasure this thread....The problem lies with me, the fact
That I am In a mans world learning guy things...Secrets if you will...Thank you all for your help.
lilshawn:
nothing secret, just foreign. I spread my interests out over a wide variety of subjects. If you work everyday doing one thing you know everything about that one thing. I know a little bit about everything.
I'm sure even ditch diggers know more about ditches than I could possibly know. ;D
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