build a magnetizer/demagnetizer

Jan 06, 2004 3 Replies
R

I'm following Birk Peterson's published plans (Machinist's Workshop April/May 2003) to build a magnetizer/demagnetizer using the coil from a surplus solenoid. On first pass it worked real well but after two or three 2 second cycles it burned up the coil. The coil came from a big Dormeyer intermittent duty relay. If I use a coil from a continuous duty relay will it survive longer?



Any advice?



It's a 115 Vdc circuit with a bridge rectifier to energize dc to mag and A/C to demag.



Thanks in advance.



Rick


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J

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A

Magnetising ?

Doh ! No wonder it failed. Try to find a design from someone who has something resembling a clue.

You don't need a constant field to make a magnetiser, you need a unidirectional field. So long as it retains the same polarity, a pulsed field is OK.

A solenoid winding (relay, transformer or motor) is a reactive load, which means that it has a higher impedance at AC than at DC. For AC, even at 50Hz, this impedance limits the current. Run it on DC though and it's the same as sticking a fairly short length of copper wire straight across the supply - no wonder it burned out !

Most decent magnetisers are pulsed, using a capacitor bank. Real ones also monitor the winding temperature, or else limit the duty cycle.

-- Smert' spamionam

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B

I built a demagnetizer by making a coil of some (16ga?) magnet wire that I had laying around. Its resistance is way too low to connect to 110 directly, so I connect it in series with a high-wattage device. E.g., a blow dryer. Works fine. Bob

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