Winding a strong electromagnet

[TinselKoala]

Yes, I got that now, thanks, in fact I got it a page or two ago.
So there are the same number of turns, half with one strand and half with the other, just more current because of the lessened resistance.
So why not do it again, split that wire into 4, or even 8 short lengths, heck, just use a single turn of 16 tiny short wires in parallel!! Heck, just wind the armature with multi-stranded wire...

I wonder why they don't.
I think there's a tradeoff there somewhere...

[Xaverius]

Yes, I got that now, thanks, in fact I got it a page or two ago.
So there are the same number of turns, half with one strand and half with the other, just more current because of the lessened resistance.
So why not do it again, split that wire into 4, or even 8 short lengths, heck, just use a single turn of 16 tiny short wires in parallel!! Heck, just wind the armature with multi-stranded wire...

I wonder why they don't.
I think there's a tradeoff there somewhere...

That's right, why stop there, you can use as many wires in parallel as you desire.  Not only will you reduce resistance but you will also reduce reactance which is much greater than resistance in an AC application, that is if you are using and AC power source, or pulsating DC.  Of course if you are using ferrite or laminated steel the reactance in not an issue.

@ TinselKoala, Kator, gyasulun and CapnHook, I owe an apology.  I believe my examples are becoming confusing.

In the wiring scheme, consider this.  10 V,  1 lenghth of wire 80 feet @ 4 ohms.  Number of turns = 100.  Amperes = 10/4=2.5A.  10 x 2.5=25W

Ampere-turns=250

If another 80 feet lenght of wire is coiled on top of the first wire and connected to the first wire in parallel, the total resistance now becomes 1 divided by 1/4 + 1/4=2.  10V/2=5A and number of turns is NOW 200.  10 x 5=50W

Ampere-turns=1000

250AT/25W=10AT/W    1000AT/50W=20AT/W

You could look at it like you have one 160 feet wire to start with, divide it in two and wind two coils on top of each other, wire them in parallel but that is a harder way to understand it.

[capthook]

So in your example, you propose AT/W is 2x.

In the wiring scheme, consider this.  10 V,  1 length of wire 80 feet @ 4 ohms.  Number of turns = 100.  Amperes = 10/4=2.5A.  10 x 2.5=25W
Ampere-turns=250

If another 80 feet Lent of wire is coiled on top of the first wire and connected to the first wire in parallel, the total resistance now becomes 1 divided by 1/4 + 1/4=2.  10V/2=5A and number of turns is NOW 200.  10 x 5=50W
Ampere-turns=1000

250AT/25W=10AT/W    1000AT/50W=20AT/W

But is it really?  If total amp draw is 5A and you have to wires in parallel, that means the 5A will be split between the two wires meaning 2.5A on each?
AT = (100x2.5)x2 = 500 AT
500AT/50W= 10AT/W  - the SAME AT/W as the 1 coil
??

So again, muti-wire coils/multiple coils will increase AT for a given coil dimension.
But it will NOT increase AT/W........
(double the AT but double the watts)

??
- - - -
If not: (if my above point is shown incorrect)

How might the winding of the 2 lengths of wire differ?  Which would be preferred?

#1: Should it be wound 1 full coil, then the 2nd coil over top of that?
#2: Wound as 1 coil with 2 wires in hand at the same time.
#3: 1 full coil 1/2 the length of core then 2nd coil the 2nd half length of core.

#1. the 2nd coil is futher from the core thus the ampturns are less effective, reducing the actual ampturns of the 2nd coil by x%, meaning the total AT/w boost is not 200% but only x%?

#2. the width of separation of between turns of each individual wire turn is now 2x, so the density of amps per turn of each wire is less meaning AT is reduced by x%?  Might the field of each wire interact with each other?

#3. Coil 2 is going to be way less effective as it is so far away from the 'active' end of the EM?

Or none of the above apply, it's all relative.  But the preferred winding style would be: #1 or #2? (I vote #2)

Might some of these possible 'issues' mean there is a practical limit to the number of wires/coils used?  What might be the limiting factor of the number of wires used?  Why?

[Xaverius]

So in your example, you propose AT/W is 2x.

But is it really?  If total amp draw is 5A and you have to wires in parallel, that means the 5A will be split between the two wires meaning 2.5A on each?
AT = (100x2.5)x2 = 500 AT
500AT/50W= 10AT/W  - the SAME AT/W as the 1 coil
??

So again, muti-wire coils/multiple coils will increase AT for a given coil dimension.
But it will NOT increase AT/W........
(double the AT but double the watts)

??
- - - -
If not: (if my above point is shown incorrect)

How might the winding of the 2 lengths of wire differ?  Which would be preferred?

#1: Should it be wound 1 full coil, then the 2nd coil over top of that?
#2: Wound as 1 coil with 2 wires in hand at the same time.
#3: 1 full coil 1/2 the length of core then 2nd coil the 2nd half length of core.

#1. the 2nd coil is futher from the core thus the ampturns are less effective, reducing the actual ampturns of the 2nd coil by x%, meaning the total AT/w boost is not 200% but only x%?

#2. the width of separation of between turns of each individual wire turn is now 2x, so the density of amps per turn of each wire is less meaning AT is reduced by x%?  Might the field of each wire interact with each other?

#3. Coil 2 is going to be way less effective as it is so far away from the 'active' end of the EM?

Or none of the above apply, it's all relative.  But the preferred winding style would be: #1 or #2? (I vote #2)

Might some of these possible 'issues' mean there is a practical limit to the number of wires/coils used?  What might be the limiting factor of the number of wires used?  Why?

You have very valid points.  I guess I am getting ahead of myself.  Your reference to "AT/W" I distorted somewhat.  Actually the example of 1000AT/50W or 500AT/50W is related to the Magnetic Field Strength which grows the magnetic force geometrically according to wattage.  As the wattage increases, H (magnetic field strength) produces more magnetic force with the square of the increase.

250AT/25W has 1 unit of magnetic force.  500AT/50W has 4 units of force, yet the amount of input has doubled. (25W to 50W)  And yes, the AT/W ratio is the same @ 10.

You're right the two parallel wires reduce to 250AT each for a total of 500AT, 1000AT simply relates to the total input, NOT the effective input.

I think method #2 would probably be most effective as the two wires would have equal spacing from the core.  The distance away from the core reduces the amount of flux influence.

Method #3 would be like two small EMs back to back so would only have half the magnetic flux.

I'd say there is a practical limit as to the number of wires used, mainly the distance of the windings from the core.  Too many wires, too much distance so you would have to carefully balance the number of wires, number of windings, wire thickness and so on.

AT/W may stay the same and total power used may increase but total magnetic force would increase even more.  This would be advantageous with a solenoid or a motor pole where a large amount of force is needed to overcome the resistance of a generator in order to produce the needed wattage.

[TinselKoala]

Um-hmm, now you are getting it.
So you can see why it made sense for us kids to rewind our motors with fewer turns of thicker wire, because that was the most effective way to reduce the resistance and thus increase the current, thereby increasing the effective A/T. And it worked, too. The rewound motors would be significantly stronger (more torque, faster acceleration) than the stock ones with more turns of finer wire.