Expert: cleggsan - 5/25/2007

Question
I'm wanting to build a round electromagnet that is 3" in total diameter (coil included).  I want to make the most powerful magnet possible to run off the power of a car battery.  What gauge wire should I use to get the maximum number of turns without overheating the wire?  What size
core (width and length) should I use and what material?  What will the approximate hold (LBS) be?  Any other design specs/tips you can provide would be helpful.  Thanks!!

-Brady


Answer
Here is one design approach for producing strong field strenght in an open gap of a laminated iron core:

http://www.geocities.com/CapeCanaveral/2404/design2.html

There is a wide variety of configurations.  So, it will depend on the geometry of your core and what you want to do with the magnetic field (focused or broad for picking up large objects, etc.). You can see some varieties here.

http://physics.kenyon.edu/EarlyApparatus/Electricity/Electromagnet/Electromagnet...

Here is a  real basic design course (high school level) that may be too low for your level of technical understanding, but it covers some basic ideas.

http://ditc.missouri.edu/designTasks/electroMagnet/index.html

This is a more advanced design guide for your consideration:

http://www.magnetsales.com/Design/DesignG.htm

Arnold, who makes many, many core designs, publishes a couple of manuals that may help, also.  Big downloads, but they are well worth your study.

http://www.grouparnold.com/mtc/manuals.htm

So, what am I saying?  The design of an electromagnet is very subjective and depends so much on what you want to do with it (application oriented).  The actual design is somewhat empirical and requires some experimentation and measurement in order to hone in on the final design and criteria.

So, the questions you must ask yourself are:

- What kind of surface does it need.
- What kind of gap or plate is contemplated.
- What are the current limitations.
- What are the duration cycles (to determine heat build up).
- What type of wire to use (enamel coating is best for density of the coil, but heat restrictions are important consideration.)
- What kind of flux or magnetic strenght build up time (if coil is big with lots of turns it will produce big magnetic field but may take a few seconds to build it up because of the inductance of the coil).
- Stray field.  If close to tv or other apparatus the magnet may need to be in a shielded invironment to prevent interference problems.)
- Design goal and geometric configuration requirements.

Maybe this will help you zero in on a design concept from which you can decide more precisely how to obtain core parts and wire sized to experiment with.

Hoping this is not confusing, but it is NOT an easy nor straighforward design project.

Best wishes,
C