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« on: May 27, 2012, 06:32:48 AM »
Another little project for a rainy day.
After trying one of Art’s ideas of wooden clock gearing using small magnets instead of teeth I encountered a problem. First, one of my small screwdrivers became magnetic then it spread, like a virus, to most of my other small bench tools and having used some steel wool (on a previous occasion) almost all my tools were picking up minute, unwanted steel whiskers.
Having seen a de-magnetizer project on eHow I set about making one and this is how I did it.
Taking an old, unwanted, mains power unit (from a long gone printer) I removed the transformer. The Mu laminations were carefully removed, the ‘I’ sections discarded (well some have been kept as lathe tool packing pieces) and the ‘E’ sections replaced, all in the same direction. The first ‘E’ is the hardest to remove but don’t worry if it is damaged or bent because on replacement they all fit back, except one, so the damaged one can be discarded.
It is only the mains, primary, winding that is used so the secondary windings are just left open circuit.
I fitted a small piece of iron onto the centre pole using epoxy then cut an appropriate sized hole in a project box and glued in the transformer again using epoxy.
When the transformer laminations layout is altered in this way, the whole flux pattern is changed and as a result it is necessary to limit the current flowing through the winding. This is best achieved by using a mains rated capacitor, connected in series (the larger the capacitance value the larger the current and visa versa). The original mains lead was re-used and the de-magnetizer was tested - it works just beautifully and removed all the residual magnetism from my small bench tools in just seconds.
The capacitor I used was a 2uF 400Volts starter capacitor and this is connected in series with the coil. Incidentally if the capacitor used does not already contain a shunt resistor then a 1 Megohm 5W resistor should be fitted across the capacitor to discharge it once power is disconnected.
Tweakie.
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