# Calculating the number of turns and thickness of an electromagnet

1. Apr 25, 2012

### anru

I'm working on a homemade electromagnet, to use on my racecar
I want to calculate the number of turns of an electromagnet and the thickness of the wire.

But i have tried to search arround in books, and can't really find any thing.

I know my wire is 0,114mm and dimensions for electromagnet is

Hight: 7mm
width: 12mm
lenght: 57mm

The form is like a horseshoe, but with 90* edge. Picture is linked:

http://oi47.tinypic.com/15zqlv8.jpg

My material of the core is steel (ignore the fact about type of steel)

I have 0,7 ampere for use.

2. Apr 25, 2012

### Bob S

Please review the equations for the magnetic field strength B in the attachment. In particular, understand the derivation of equation (6).The important parameter of the coil is NI, the product of amps times turns.
Please review the copper wire gauge table at http://www.powerstream.com/Wire_Size.htm
Your wire diameter (0.114 mm) is roughly 38 Ga. However, you will need 22 or 24 Ga. copper to carry 0.7 amps.

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3. Apr 25, 2012

### anru

i want to calculate number of turns

4. Apr 25, 2012

### Bob S

Make an engineering sketch of your electromagnet including coil dimensions. Select the proper copper wire gauge from the copper wire table. Using the wire diameter, calculate the number of turns you can fit into the space for the coils. Using the calculated length of the wire, calculate the wire resistance and the voltage needed to get 0.7 amps. Now calculate the amp turns. Using equation (6) in my earlier post, is the magnet strong enough?

5. Apr 25, 2012

### anru

The G stands for Gauge or what?

6. Apr 25, 2012

### Bob S

The first column in the wire gauge table is the wire gauge (Ga.) number. The third column is the wire diameter in mm. The fifth column is the ohms per 1000 meters. Use column 7 for the maximum amps in a coil.

7. Apr 25, 2012

### anru

This is my data
37 0.0045 0.1143 523.1 1715 0.17 0.0289 1350 kHz

And what should i do then?

The one with AWG 37

8. Apr 25, 2012

### Bob S

So your wire selection is 37 Ga.?

1) How many turns can you fit into the allowed dimensioned space for your coil?
2) What is the estimated wire length?
3) What is the estimated wire resistance?
4) Using the recommended maximum wire current 0f 0.03 amps, calculate the the required voltage.
5) Calculate the amp-turns of the coil.
6) Using equation (6). calculate the B field.

9. Apr 25, 2012

### anru

thanks bob :-)

10. Oct 2, 2013