A Useful Workshop Helper

ave you ever had the experience when working at your bench that every time you put your screwdriver down it picks up a screw, or a nut, or a washer, because it is magnetized. I have, so years ago I built a demagnetizer from a 1500-ohm electro-dynamic speaker field coil and used it for many years. Later I got the idea of building a Magnetizer / Demagnetizer.

This time I could not find a field coil in my junk box so I used a coil from a three-phase electric motor starter (contactor coil), a center off single pole double throw switch ( better if you have a spring return to center position switch), two red light emitting diodes, a 150 ohm 5 watt resistor and two 1000 PIV 1 amp diodes.

Construction is simple. All the components are fixed in a plastic case with a hole cut in the bottom and top cover to allow the tool to be magnetized or demagnetized placed within the coil. The 150 ohm resistor is used to limit the current in the LED’s to a safe value, while the two 1000 PIV diodes are installed because the inverse peak volts which can be very high. A hot glue gun is very handy to fix and insulate the small components even the coil can be fixed that way or you can used an epoxy resin cement.

Coil	240 volt AC supply 440 volt coil	117 volt A C supply 230 volt coil
Diodes	2 x 1N4007 diodes	1 x 1N4007 diode
Light Emitting Diodes	5 mm red LED’s	5 mm red LED’s
Switch	SPDT center off	SPDT center off
Resistor	150 ohm 5 watt	150 ohm 5 watt
Case	Zippy box to suit	Zippy box to suit
Flexible Cable	240 volt 3 core cable	117 volt 3 core cable
Power Plug	plug to suit supply	plug to suit supply

The use of this device is simple to magnetize. Switch the switch to the diode section and one LED will light and the tool will be magnetized. To demagnetize, switch to the straight through position and both LED’s will light and the tool will be demagnetized. It is simple as that, but DON’T forget to turn it off after use!

This is a very handy little device and I use it all the time when working in the workshop. It is handy to be able to magnetize a screwdriver to pick up screws or small objects and when you are finished to demagnetize the tool and store it back in a demagnetize state

Above is a view of the workshop showing a computer in a homemade chipboard tower case. Also, most of my Test Gear is home built.

If you build one of these devices you will find it extremely handy, but remember that it can be used only intermittently because inductance is not high enough to limit the current in the coil and it would soon burn out if left turned on too long.

WARNING: Do not build in a metallic box as the coil would induce eddy currents into the box and the inductance would be lowered and the load current would increase. Ground any exposed metal for safety's sake. Even the switch shaft as with all power supply voltage can be lethal.

Biography of Bruce Holland, VK2ZAD
vk2zad@ozemail.com.au
12 Greenoaks Road,
Narara NSW AUSTRALIA 2250

I showed an interest in things electrical and electronic from a very early age. As a pre-school child I still remember placing a wire hair-pin into a power outlet at my grandparent’s home to see what would happen. It was an anticlimax a little spark then no power in the house, but did I get a hiding? Yes sir I did!

There were other things that happened to me in my childhood but I will not burden you with them now, but to tell you that when I was eight years old my father built a crystal radio set for me. It somehow clicked for me and from then on I was a radio enthusiast and after six months I knew more on the subject than my father did and went on to build one valve radios with regeneration much to the annoyance of the neighbors.

During World War 2, I built radios with 3 valves (detector, output and rectifier) using valves I "borrowed" from my Uncle’s radio. He was on active service and left his stuff for safe keeping at our family home, so I kept the valves nice and warm even extremely hot when I managed to get the screen grids red hot once.

When I started work as an Apprenticed Electrical Fitter in 1943 I was able to buy components when they were available (there were shortages due to the war). When I had accumulated enough parts I built my first Superhet receiver. From then I went to bigger and better things.

In 1954 I sat and passed my Amateur Radio Examination and received my call VK2ZAD in March 1955. In April 1956 I was ordained into the Anglican (Episcopalian) Ministry and served in country parishes until 1981 when for medical reasons I resigned to live on the coast and was employed in the NSW TAFE system (Technical College) as a Electrical Trade Teacher in the School of Applied Electricity for ten years until I retired in 1991.

My wife Elaine and I have two sons: Ralph VK1BRH and Mark and three grandchildren Fiona, Steven and Catherine. I have been a home-brewer most of my life and only started to buy commercially built equipment in the late 1970’s . I have built and used home-brew gear on 6 meter, 5 meter, 2 meter, 1 meter and 70 cm bands at various times, AM, SSB, FM and now packet, who knows what next?