# Coils

Discussion in 'General Electronics Discussion' started by restio, Jun 8, 2013.

1. ### restio

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Jun 8, 2013
Can you please explain to me how wire size and number of winds is determined when winding an induction coil. My aim is to have magnets driven up and down in this coil.

2. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
The larger the wire size for 'n' turns on an iron core the more powerful the magnetic field will be. It will also demand more current from your power source.

Chris

3. ### poor mystic

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Apr 8, 2011
I hesitate to say that another member is mistaken, but the thickness of the wire has no direct effect on the magnetising force. Apologies, Chris!
If a fairly technical discussion suits you, try: http://en.wikipedia.org/wiki/Electromagnet
Otherwise, magnetic force is proportional to N*I. N is the number of turns of wire wrapped around the core, and I is the amount of current. So doubling the number of turns, or doubling the amount of current in the wire, will double the strength of the magnet.
However! There is a limit to the strength of an electromagnet wrapped around a core, and that limit is the amount of magnetic flux which the material will carry.
It might sound tempting to try a magnet with no core whatever, but free space is not a good 'conductor" of magnetic flux, so vast currents and impossible numbers of turns would be required to get much strength.
Mark

4. ### restio

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Jun 8, 2013
Perhaps I used induction the wrong way. I intend having the permanent strong magnets cycling up and down in the coil in a toroidal-ish shape.

The issues I see is the distance between the magnet track and wires surrounding it should be small. Then there needs to be turns to expose maximum current carrying runs that can take the current in the field area.
So a 1 SWG will have less turns in the field, but it would have competence to carry current.
100 SWG would have 100 times the turns and arguably more space filled, but may get hot as it can't stand the current and burn out.

So I wondered if there's a formula for it, cos it seems .4mm in bulk in wire seems a bit hard to source in Adelaide, Australia.

5. ### duke37

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Jan 9, 2011
I do not see how a magnet can cycle up and down in a torroid. Do you mean a cylinder?

There is a limitation to the size of the coil. You should fill the available space for the best efficiency. You can use lots of turns of fine wire with low current or a few turns with thick wire and a lot of current. As previously said, the voltages will be different but the power will be about the same.

There will be no such thing as 1 SWG and 100 SWG and if there were, the difference in area would be millions not hundreds.

4 mm (8 SWG) would be so thick that you would need a machine to wind it. If you must go for very few turns, then you can make a cable by twisting 7 strands of thinner wire and using that as one wire. It is easy to get into a mess !

You should keep the magnetic gap small as you say. Look at how a loudspeaker is made. Here the magnet is stationary because it is heavy and the coil moves in a very small gap.

6. ### poor mystic

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Apr 8, 2011

A drawing might help us a lot. Your design aims and criteria would help, too.
There certainly is a method for calculating the magnetic flux in a given magnetic circuit. The most important result in my opinion is that air gaps are like multi-megohm resistors, while iron cores are like good wire.

7. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Mark, I don't see how my statement conflicts with yours.

Chris

Last edited: Jun 9, 2013
8. ### restio

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Jun 8, 2013
NCDrive I think the explanation of the difference is it is the number of turns, of whatever size wire, the number of turns with big wire is less, so less power output with big wire than fine wire in many turns filling the same place.

Say a wind turbine has been converted to a circular vertical movement and a cam setup has a stack of stong permanent magnets going up and down in this cylinder.

So I think I have found what is important, and yes a cylinder is the best description.
Minimum space between moving permanent magnets and the inside of the wire cylinder.
More turns in the cylindrical space means more power, so thinner wire.
More cycles of the magnets means more power
Uplift of the magnets produce one polarity, down produces another so a diode bridge will rectify to DC

Cheers

9. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
If you're attempting to build a reciprocal motion generator it will never achieve the efficiency of a rotary generator. In fact it won't even come close.

Chris

10. ### duke37

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Jan 9, 2011
As I said before, you an fill the space with thick or thin wire. The power output will be similar.

Thick wire will give a high current but low voltage.
Thin wire will give a high voltage but low current.

If you are going to use a bridge rectifier which will drop some voltage, then thin wire and high voltage out is preferred.

11. ### restio

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Jun 8, 2013
Thanks guys, perhaps I will be gearing up the rotary motion, using a lot less wire and rotating high strength magnets, use iron filings to find the force lines to bisect with wire.

12. ### duke37

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Jan 9, 2011
If you play with iron filings and a strong magnet, then you will have trouble.

If you wish to do so, then place the magnet in a plasic bag and then when the experiment has ended, the magnet can be taken out of the bag, leaving the filings behind.

13. ### restio

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Jun 8, 2013
good clue Duke, the old glad wrap gets into a lot of industrial solutions in an isolating function.