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How many turns to produce power on a spinning coil

  1. Aug 2, 2017 #1
    Does anyone have formulae to calculate the number of turns required on a coil to produce 10V at approx 5W.
    I wish to have a coil spinning on a 16" diameter former in a 0.25 gauss magnetic field at a minimum of 2.2Hz. I need to be able to work out the size of coil and number of turns to produce approx 5W at 10-15V which will be DC rectified (frequency is not important).
    The former is provided with a mechanical rotational force of between 2.2 - 16.6Hz. The magnetic field will vary between 0.25 - 0.65 gauss, but will be constant and parallel across the 16" former.
  2. jcsd
  3. Aug 2, 2017 #2


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    Google "motor design calculator". There are many of them.

  4. Aug 2, 2017 #3
    Thanks Anorlunda. I tried that but it gave me loads of motor calculators and I need generator calculations.
    See attached. A coil on a rotating former in a low magnetic field. How small can I make the coil but still generate 10V at 5W approx.

    Attached Files:

    Last edited: Aug 2, 2017
  5. Aug 2, 2017 #4


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    Perhaps see...

    One thing to watch out for is the resistance of the coil. You may need to correct for the voltage loss.

    I should add that that web page isn't great but should give the basic idea.
  6. Aug 3, 2017 #5
    Hi CWatters,
    That is great. I have looked at this, the issue I find with all these types of data is the way the coil moves in the magnetic field.
    The diagrams show a coil as a single loop where one side is moving from N to S while the other side is moving from S to N of the magnetic field.
    In my case, the coil is moving in it's entirety through the N to S field before then moving through the S to N field.
    Without experimenting, what is the best orientation of the coil to get the best performance? What is the smallest size I can make the coil without losing the power required (although this is small).
  7. Aug 3, 2017 #6


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    I did a ball park calculation using the equation from the above link. I assumed the voltage required was 20V, the coil diameter was 0.1m (4") and it rotates at 2Hz (120rpm). I got a huge and impractical figure of 5 million turns. Due to the way your coil moves this would be an under estimate. Sorry but I think the mag field is way too weak to do what you want.
  8. Aug 3, 2017 #7
    Thank you. I will have to rethink the strategy.
    Was the equation you used N=-1*(-V/Δ((tesla*area meters squared)/seconds))?
  9. Aug 3, 2017 #8


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  10. Aug 16, 2017 #9
    I been working on portable generator for the last couple of months and this is what I came up with
    The rotor has about 100 turns to produce 110vac so it's close to 1 turn per volt
    I'm still working on it so I hope I am right
    Hope I'm right
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