Coil Winding Efficiency 3

[BobM2]

Given a spool with a specified ID, OD and length and knowing the diameter of the magnet wire, is there a formula that will state how many turns you can get on the spool? I would think it would vary quite a bit depending on the quality of the winding process (how "tight" it is).

 

[ronnie497]

Bob,

You are right in saying that the winding process determines the amount of wire that can fit. As long as the winder conforms to the "layer" winding technique, you can come quite close as follows;

Turns per layer = length/OD wire.
No of layers = radial hight/OD wire.
Total turns = Turns per layer * No layers.
Length Mean Turn = ((ID coil + OD coil)*Pi) / 2.
Length of wire = Total turns * Length Mean Turn.

Note:
1 Use the covered diameter for the wire.
2 Round answers down to iteger.
3 This is based on the assumption that the layers are aligned as follows;

O O O O
O O O O

The winder will usually wind as below which means that you could get a bit more on;

O O O O O
O O O O O O

 

[jbartos]

Suggestion: Some allowance on the coil radial hight will be required if there are insulation layers among the winding layers. The insulation thickness has to be added accordingly. Then,
O O O O
O O O O
applies only.

 

[CarlPugh]

Turns per layer = length/OD of wire -1
(The -1 is significant when there are few turns)

If layer insulation is used, the layer insulation will overlap and there is an additional factor besides the thickness of the layer insulation.

Quality of the winding process is important like BobM2 stated. Fill factors as low as 60% are sometimes recommended.

 

[jbartos]

Comment: The insulation layers somewhat protect conductors insulation during the coil winding process since there are tensions under which the conductor is being formed into a coil.