1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    Staff: Mentor

    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 by a moderator: Aug 2, 2017
  5. Aug 2, 2017 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted