|Magnetizer / demagnetizer|
Surely magnetized tools have helped you many times, the best example is definitely a screwdriver. When you drop the screw in inaccessible location you can easily pick it up with magnetized tip of screwdriver. Even if not magnetized, it is very easily done just by touching the strong permanent magnet. And what to do when this feature bothers you, when you work in a small space, and small bolts and nuts keep sticking to the screwdriver tip? Continue reading and find out how to make simple device that will help you solve both problems.
We know that metal is demagnetized by exposure to alternating magnetic field and also magnetized by direct exposure to the DC magnetic field. Schematic of the device that creates such fields is on the picture below.
The working principle is very simple. When the coil is powered with AC current alternating magnetic field is created. This is the case when the selector switch is in position “1”. In another case, when the switch is in position “2” current flows through the diode D1 and gets a half-wave rectified. Such direct current creates a DC field in the coil.
The most important component that you need to get is the coil. Any one that runs on desired voltage can be used. My on the picture below was taken from the 230V motor that drives washing machine mechanical controller. Motor is 3.5 VA, the coil resistance is 1500R. You can find them at:
• ovens where they are used to drive an electric spit
• microwave oven where motor turns the glass plate
• washing machine where motor is rotating the mechanical controller (my case)
Also coils from electromagnets and power relays can be used.
Any suitable case can be used, it is important that is made of plastic for insulation and protection from electric shock because the device is connected to the mains voltage of 230V. If you want hold device by one hand it is desirable to be smaller in size and elongated shape as shown on pictures below.
It is necessary to get single pole changeover switch with a stable off position in the centre, also called the SPCO and 1-0-2 switch. Perhaps a better option is to get push button changeover switch which is automaticly returned to the center position. The important thing is that switch must be rated for voltage of 230V and switching current 2A, everything more than that is better.
The selected diode is well known 1N4007. Maybe a better option is to install rectifier circuit for full-wave rectification but I have achieved good results with a single diode and half-wave rectification so there is no need for that. If you use a little stronger coil it would be wise to put two diodes in series because the inverse peaks from coil can be very high.
Every cable that you can find laying around will be OK. Cable with plug and two wires without protective ground is used in my design because the device is enclosed in a plastic box and there is no risk of electric shock.
First you need to cut holes on the box for fitting all required parts. Box is made of ABS plastic so small saw and a scalpel will do just fine for all the cutting.
The next step is to connect all the components by the schematic given above. Use heat shrinks for isolating joints that mustn’t be connected by accident inside the box. An example of my solution see on the picture below.
Place everything in a box. The cable and switch are made to be mounted into these kind of boxes, so there should be no problems. But the coil is not, so you will probably have to glue it on box with hot glue gun or something similar.
Close the box, tighten the screws and the device is ready for use. It is recommend to check all connections with a multimeter before connecting to mains power just to make sure there is no short circuits.
See below short video of device working: