Soft Circuit Workshop

Adhering Wires to Magnets for Use as Electrical Contacts

Using magnets as switches can provide many advantages.  Though Magnets can firmly hold contacts together, they are easily pulled apart and possibly stowed on alternate, non-electrical magnetic surfaces.  Magnets are relatively inexpensive fasteners for their strength, and Properly polarized magnets can automatically force proper connections (postive to positive, ground to ground).  Magnets are used in a multitude of devices, and can be easily scavenged for re-use…particularly “rare earth”, or neodymium iron boron (NIB) magnets.  (For more info on the widespread use of NIB magnets, see http://www.dansdata.com/magnets.htm.)

Neodymium magnets are coated in nickel, which is highly conductive, but most standard “Refrigerator magnets” are generally not because they are made out of ceramics…although some cheap magnets are made out of black ferrite and are conductive as well.  Unfortunately, high temperatures can cause neodymium magnets to demagnetize.  This is likely only a problem because of the high temperatures required to solder to the nickel itself.  It may be possible to solder directly to a nickel-plated magnet without raising the temperature to damage-inducing levels, but it would require a strongly acidic solder flux.  To avoid this toxic and potentially material-damaging situation, there are two other solutions available:  conductive epoxy, and magnet encasement.  Magnet encasement entails creating small metal “cups” that can be crimped around the magnet and soldered to separately.  However, unless this is done properly, the magnet may have the ability to move around inside the cup and lose contact intermittently.  For this reason, I will focus on the use of silver-laden conductive epoxy in this report.  The epoxy I used is made by MG Chemicals, and is sold by LessEMF.com (http://www.lessemf.com/paint.html).

Conductive epoxy is more expensive than standard epoxy, and does not harden to the same consistency.  The method of application is similar, however.  Two syringes full of epoxy ingredients are to be vigorously mixed in equal amounts, and quickly applied to the joining surfaces.  However, the “pot life” of the epoxy (the time until the epoxy has solidified enough to not stick to other surfaces) is only five minutes.  Thus you should prepare your wire first.  In my case, I was attempting to adhere a magnet to the small ends of modified earphones.  This required burning off the outer insulation of the wire and bending it into a loop.  I cut and sanded some wood to act as a mixing stick and an applicator stick to aid in creating the contacts.  I then used the applicator to spread the epoxy evenly over the magnet’s surface while holding the wire down:

Even when just mixed, conductive epoxy has the consistency of very sticky wet mud…much stickier than regular epoxy.  What makes this job even more difficult is the face that you can not use steel metal tools to hold the magnet down, as it will simply stick to the tool.  It took me several attempts to realize that placing the magnets on a steel surface to hold them still is a good strategy.

Once the Epoxy is sufficiently applied, you must wait at least four hours until the epoxy has “cured” (completely hardened).

I waited nearly 24 hours, yet I still found that the silver in the epoxy easily rubbed off on my hands.  (This may be due to not mixing the two ingredients in EXACTLY the same amount, but I am not sure.)  To avoid the slow erosion of the material, as well as provide some insulation, I coated the hardened epoxy in hot glue (this time using the steel surface to hold the magnets):



The result is not pretty, but could eventually be covered in an additional protective layer of heat-shrink tubing.

In my first attempts, one of the magnet’s cured epoxy completely separated from the magnet’s surface within a few minutes of testing.  Before re-applying epoxy, I used a metal file to roughen the magnet’s surface.  This would presumably facilitate the epoxy’s ability to “grab hold” of the surface, and is how I should have prepared the magnets’ surfaces initially.