General coil winding question

[captainpecan]

I am trying to wrap my mind around a physics problem. I am deciding the best way to wrap coils for a new motor build. I am not finding the answer I am searching for anywhere and I have had a couple different responses when I've asked this so I am a little unsure on the math. There are some great minds with tons of experience in here. Can someone please try and explain to me the correct way to do the math here?

The coils I am winding are just going into a new axial flux motor design I am trying. The coils will be serpentine wound so there could actually be 5ft wire per turn. But exact numbers here aren't as important because I may change some things after I know the correct way to figure the math. I will be using 30 awg magnet wire that carries a high resistance of 102.3 ohms per 1000 ft. I want to use thin wire to get more turns in a smaller space for more magnetic flux. But the trade off is that the current is severely affected due to the high resistance as i add more turns.

I think I can compensate for this problem by simply winding with parallel strands of wire. The problem I have is that I am getting two different answers for how much it effects it and I am unsure of which is correct.

Let's say I have a coil of 400 turns and is 120 ohms. If I split the coil into 2 strands, the overall resistance is cut in half. So now I have 2 coils of 200 turns each for a TOTAL of 60 ohms. Here is where I am confused. I have a source that says that because the 2 coils are in parallel, I then cut the resistance in half again for a total of only 30 ohms because of how the flux works together. Is this correct? Or do I only cut it in half once? It makes a difference for deciding the turns and the current I want it to draw. I would like to learn this lesson BEFORE I wind all my coils and learn the hard way like I usually do.

The point of this experiment is simply trying to get as much magnetic field from the coils as possible without adding any extra current. If I can cut the resistance in half for the same amount of wire using 2 strands, I also double the current. If I then double the amount of turns, I get back to the same amount of current used, but now I have doubled my ampere turns and doubled my flux output. Thats the theory. Increased efficiency that only costs me copper and space, not current.

Any help with the math here is appreciated. I would like to make a decision this weekend and begin winding. Thank you for any help in this.

[skywatcher]

It depends on the details... for many applications only the 'amount of copper' counts, which means it doesn't matter if you use more turns of thin wire, or if you use less turns of thick wire. So you will need more voltage, or more current in one case or the other.


The only difference in both models is inductance. Of course a coil with more turns has higher inductance. So it depends in the frequency you want to use, what inductance is necessary or acceptable for your application.

[captainpecan]

Well, in this case it doesn't really matter to me. Amount of copper OR number of turns. Because both cases would be valid here. It's the resistance I'm questioning. I know the resistance is halved with 2 strands. But is it halved a second time because it's parallel wound? I'm sure it has to do with inductance amd how the fields interact. I'm just not sure how to predict the resistance. I feel like it would only be halved once, but it seems when in other projects I hook two coils in parallel, more than double the current flows. I think anyway. I just want to understand that concept better.

But, the goal is to get more copper and more turns with more flux for the same voltage and current by modifying the resistance. It's what I'm working on anyway.

[bistander]

...
Let's say I have a coil of 400 turns and is 120 ohms. If I split the coil into 2 strands, the overall resistance is cut in half. So now I have 2 coils of 200 turns each for a TOTAL of 60 ohms. Here is where I am confused. I have a source that says that because the 2 coils are in parallel, I then cut the resistance in half again for a total of only 30 ohms because of how the flux works together. Is this correct? Or do I only cut it in half once? It makes a difference for deciding the turns and the current I want it to draw. I would like to learn this lesson BEFORE I wind all my coils and learn the hard way like I usually do.
...

Hi CP,
For example purposes, say each turn is equal length of wire. Then:

400 turns, 1 wire, 120 ohms.
200 turns, 1 wire, 60 ohms.
200 turns, 2 wires, 30 ohms.
400 turns, 2 wires, 60 ohms.

For a fixed excitation (mmf or AT or Ampere Turns) the amount of copper determines the power dissipated in the coil. Varying # of turns and wire size only changes the voltage and current, not power.
bi

[captainpecan]

Thank you for the response. Exactly what I thought, except maybe your citation at the end. I was under the impression that if a coil had 200 turns at 12v 100ma it would have half the flux as one with 400 turns at 12v 100ma, even though it is exactly same power draw. Am I incorrect? I thought with the equation, if all variables stay the same except for N, the number of turns, wouldn't just increasing the turns increase the flux? Not arguing by any means, just trying to understand. Like if you ran the same current into 1 turn there should be a way less strong field than 500 turns for the same power. But maybe I am wrong? It sounds like you are saying as long as the voltage amd current is the same, the turns can increase or decrease but the flux will not change?