MikeAusC
Enlightened
I'm building a mount for a car video camera and I want the 5v DC connectiosn to make when I drop it into its housing.
So I attached 2 nickel-plated super magnets to the aluminium case using JBweld and I tested for perfect insulation after I'd placed the magnets. I assumed the epoxy would ensure insulation between magnet and housing.
I sure was annoyed when I tested again after the JBweld had hardened - one magnet measured 600 ohms and the other 1200 ohms - I assumed the magnets had pushed the epoxy aside and shorted to the housing.
Removing the magnets was NOT easy - I thought if I bent the aluminium the magnets would pop off - no way - the aluminium bent beside the magnets !!
So I applied heat from a soldering which softened the epoxy so I could prise off the magnets. This revealed at least 0.5mm between magnet and aluminium ?????
So I probed the surface of the epoxy layer that was still attached to the aluminium to find very high resistance ???? - then sudddenly there was conductivity at one point - I kept on moving the probe to find most of the epoxy surface was insulated from the aluminium - with just a few spots that conducted !!!
So I assume that as the JBweld was setting, the metal particles aligned in the magnetic field to form a 600 ohm conductor between magnet and aluminium !!!
Maybe I could have burnt out the whiskers using a high voltage zap ?
So I attached 2 nickel-plated super magnets to the aluminium case using JBweld and I tested for perfect insulation after I'd placed the magnets. I assumed the epoxy would ensure insulation between magnet and housing.
I sure was annoyed when I tested again after the JBweld had hardened - one magnet measured 600 ohms and the other 1200 ohms - I assumed the magnets had pushed the epoxy aside and shorted to the housing.
Removing the magnets was NOT easy - I thought if I bent the aluminium the magnets would pop off - no way - the aluminium bent beside the magnets !!
So I applied heat from a soldering which softened the epoxy so I could prise off the magnets. This revealed at least 0.5mm between magnet and aluminium ?????
So I probed the surface of the epoxy layer that was still attached to the aluminium to find very high resistance ???? - then sudddenly there was conductivity at one point - I kept on moving the probe to find most of the epoxy surface was insulated from the aluminium - with just a few spots that conducted !!!
So I assume that as the JBweld was setting, the metal particles aligned in the magnetic field to form a 600 ohm conductor between magnet and aluminium !!!
Maybe I could have burnt out the whiskers using a high voltage zap ?
