How many turns to produce power on a spinning coil

1. Aug 2, 2017

Donglin

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. Aug 2, 2017

Staff: Mentor

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

3. Aug 2, 2017

Donglin

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.

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Last edited by a moderator: Aug 2, 2017
4. Aug 2, 2017

CWatters

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.

5. Aug 3, 2017

Donglin

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).

6. Aug 3, 2017

CWatters

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.

7. Aug 3, 2017

Donglin

Thank you. I will have to rethink the strategy.
Was the equation you used N=-1*(-V/Δ((tesla*area meters squared)/seconds))?

8. Aug 3, 2017

CWatters

Yes

9. Aug 16, 2017