# Calcualting the number of magnet wire turns and layers in a coil bobbin

I'm trying to find a formula to calculate the number of turns needed in a thermoplastic bobbin to use in a electric motor. Instead of using magnet wire in the slots of a lamination stack, the bobbin can be wound on a inexpensive single flyer winder before being inserted into the lamination stack slot. Here's what I've done so far.

1. Determined what total resistance the motor needs to have.
2. Using the AWG table pick the diameter of a representative wire (until I know how much wire I need it will be a guess).
3. Using the AWG determine the resistance of a certain length of this wire.
4. I calculated using a CAD program the surface area of the bobbin that will constrain the wire.
5. Then find the elusive formula for pulling this data together.
• What specs do you have for torque thus acceleration, and inertia energy to drive current source or sink. What is Bmax for core saturation vs I to determine n turns and thus L? DCR and eddy current losses thus temp rise of windings. There are many more variables undefined in your question, losses, max power, thermal conduction, temp rise, duty factor on motor, excitation voltage, commutation RPM thus inductance, for stored electrical energy etc What other variables do you know? Apr 4, 2017 at 14:39