# How many turns should I wind on a coil

#### mega128

Joined Nov 16, 2020
4
Hi all,

I am trying a make a pulse pendulum but not sure what is the most efficient way to do that. My plan includes 2AAA batteries with some microcontroller. My main question is how to determine magnet wire gauge and number of turns to get the most magnetic field to push the magnet. I can use magnet wires as fine as 42AWG and more than 10K turns on my winding machine so I am limited to finer wires and turns etc. My main goal is to determine what AWG to choose and how many turns on a air core thread bobbin will give me the best longer battery life. I understand other factors count such as neo magnet width, strength and pendulum height etc.

Thanks all,
Jay

#### crutschow

Joined Mar 14, 2008
26,811
I think you will need to experiment to determine the needed ampere-turns for the electro-magnet.
You initially use a larger gauge wire with perhaps a hundred turns and see how much of a pulse current (amperes and pulse duration) to keep the pendulum moving.
Once you know the ampere turns for that, you can calculate the turns needed for a smaller gauge wire at a lower current.
You will need to calculate the resistance of the wire so that 3V is sufficient to get the desired current.
So it's a trade-off between wire size, available area for the wire, current, and applied voltage.

#### Dodgydave

Joined Jun 22, 2012
9,920
Are you wanting to make something like this...?

Last edited:

#### mtonge

Joined Apr 19, 2016
93
That was so cool. Now I want to make one.

#### mega128

Joined Nov 16, 2020
4
Hi Dodydave - Not exactly like this video but similar concept. - Thanks

Hi Crutschow - Thanks for the valuable information. If there a link with a calculator or website that talks about this concept in detail please share with me, else I will follow with the experimentation that you have suggested.

Thanks all

#### Alec_t

Joined Sep 17, 2013
11,984
You really don't need a microcontroller for this project. A simple circuit such as in post #3 will do the trick.

#### shortbus

Joined Sep 30, 2009
8,443
to get the most magnetic field to push the magnet
how many turns on a air core
Which are you after? The most magnetic field to push a permanent magnet will come from an electromagnet using an iron core, not an air core. I'm assuming the pendulum shown in the Youtube isn't what your trying to do, since you said you want to push a magnet on the pendulum.

#### Bernard

Joined Aug 7, 2008
5,774
Re post #7: True an iron core will increase magnetic field but might attract & hold the magnet. None of the many pendulum drives that I have seen such as " Cardboard Clock" use an iron core coil.

#### atferrari

Joined Jan 6, 2004
4,250
Iron core that could end becoming a permanent magnet itself.

#### Bernard

Joined Aug 7, 2008
5,774
I found a construction of the " Cardboard Clock" in Everyday Practical Electronics, November 2003. Several drive circuits, one and 2 coil. The coil used is 22 mm ID, 100 turns of # 32 wire.

#### Dodgydave

Joined Jun 22, 2012
9,920
I found a construction of the " Cardboard Clock" in Everyday Practical Electronics, November 2003. Several drive circuits, one and 2 coil. The coil used is 22 mm ID, 100 turns of # 32 wire.
I used to get this magazine, brilliant..

This one... https://www.epemag3.com/vault/1103.htm

#### shortbus

Joined Sep 30, 2009
8,443
True an iron core will increase magnetic field but might attract & hold the magnet.
My reply was because I'm not sure what he is actually trying to do. It took a tangent when the Youtube video was posted.

Not exactly like this video but similar concept.

#### mega128

Joined Nov 16, 2020
4
Thanks to everyone for their input. Air core over iron core was picked as mentioned above.
I using a micro controller to make it more interesting than conventional circuit diagrams on the internet.
My question was mainly about the number of turns on a coil and have found a couple of calculators and playing with them. Thanks everyone again for your time.

#### MrAl

Joined Jun 17, 2014
8,066
Hi all,

I am trying a make a pulse pendulum but not sure what is the most efficient way to do that. My plan includes 2AAA batteries with some microcontroller. My main question is how to determine magnet wire gauge and number of turns to get the most magnetic field to push the magnet. I can use magnet wires as fine as 42AWG and more than 10K turns on my winding machine so I am limited to finer wires and turns etc. My main goal is to determine what AWG to choose and how many turns on a air core thread bobbin will give me the best longer battery life. I understand other factors count such as neo magnet width, strength and pendulum height etc.

Thanks all,
Jay
This is ultimately a multidimensional optimization problem.
The variables to be optimized include:
The wire size
The number of turns
The weight of the magnet vs the strength of the magnet

One dependence is:
The applied voltage and its internal resistance

The wire size and number of turns works with the applied voltage and its internal resistance as there is only one wire size and one N number of turns that produces the maximum magnetic force from the coil. I presented this calculation somewhere else i think on this forum.
The result was that the total resistance of the coil (related to wire size and number of turns) must equal the internal resistance of the power source. Since the number of turns affects the magnetic force of the coil, that plays in with the wire size to get the maximum force using the specified power source.

The weight of the magnet plays into the scheme because of gravity. The lighter the weight the less force required to move the magnet (and lever arm). Since the strength of the magnet also enters into the force equation and the strength is nominally greater for magnets that weigh more, this will mean a balance between weight and strength would be another optimization point. The face shape will also affect the force and that will factor in with the face of the coil or coil core.

The coil core should be of high magnetically active material which will focus the force of the coil into a narrow corridor so that it has most effect on the face of the magnet. The core will become partly a permanent magnet so the minimum distance between coil core and magnet will have to be observed. This distance may be as small as zero however depending on the core and magnet weight.

So there are a number of things to be optimized here. We might go through some calculations later. We might also come up with an analogous electrical simulation scheme to test the calculations.

One final point:
Dont let anyone tell you that the true pendulum motion is linear because it is not. Since it is very close to linear however, many times it is modeled as being linear anyway.

Last edited:

#### Bernard

Joined Aug 7, 2008
5,774
If using a thread bobbin, use a plastic one. If using #24 ( much too big ), a bobbin will hold about 265 turns giving around 1 ohm, & 10 mV.
I do not have an AWG list for enamel Cu wire so est. # 34 .0051, bobbin wire cross section .15" X .27",
.15 / .0051 =29, .27 / .0051 = 53, 29 X 53 = 1535 turns, ave. length of 1 turn =1.6" , length =2456" /12 = 205 ft. X .648 ohms /ft. = 132 ohms. 3V / 132 = 22 mA, seem OK. V out about .1V.
Bobbin ( steel ) 20.5 mm OD, core about 8mm, length 7 or 9 mm.

Last edited:

#### sparky 1

Joined Nov 3, 2018
490
A Gauss meter records instantaneous pulses to a spreadsheet the test intervals make good use the microprocessor.
photo sensors indicate position. The diode would be a good idea. Comsol could show a little more about the fields.

Last edited: