Yesterday I disassembled a microwave transformer. Previous posts have discussed a need for an electromagnet capable of pulling 50 pounds or more. I think the microwave tranformer will pull in excess of 600 pounds at less than rated current (about 15 amps) and would take the current for several hours. Awesome!!!!.
The transformers came from two 1500 watt microwave ovens. One was dissassmebled and tested, the other, from a different brand and different manufactuer appeared physically identical, elecricaly different. one had an external filamant transformer, the other had filment transformerwound on.
The Transfromer was easily disassembled by using a die grinder to remove welds that held the transformer to a mounting plate. The other tranformer was bolted to its plate. I selectedthe more difficult to disassemble for the testing. The transformer is NOT like some older transformers where the E and I shapped pieces were interwoven. The interwoven types are MUCH harder to re assemble and not have a lot ofnoise. the newer style is a testiment to mass production making it easy to assemble. The I pieces are and remain in one block. same with the E pieces.
I ground the welds holding the I pieces to the E pieces completely out. The laminations were visible accross the place wherethe weld had been. The whole thing appears to have used varnish or epoxy to hold the I and E parts togehter before welding. When the weld was ground away, pried the I piece lose with pocket knife, drove the shunts (two more blocks of laminations) out and passed the knife around the insulation of the primary winding (the one with the large iwres) and it knocks off with ease.
then knock out the secondary winding (it has between 1/2 and one mile of small diameter wire, well insulated. Save it if you wish a source of small wire. The wire will handle only about 1/2 amp to one amp).
I havea varible voltage power supply and a 12 volt battery. Using the battery to pass currentthough the winding (installed on the E piece) and the I piece for a "keeper" (test bar), I was amazed at the strength ofthe pull. Way too much to break loose!.
I used the variable voltage supply to pass 10 amps through the magnet winding. With the E pice clampedin a vise and a spring scale i pulled on the e piece till scale read 60 pounds. The scale was tied with cord to the I peice. I figured i did not want that I piece coming loose, being accelerated by the spring and knocking my head off. so i reducedthe currnet to 1/2 amp (one half is right), as small a current as could supply. Pulledthe spring sale to 30 pounds and stopped (pucker factor came into play).
Since the pull should be proportional to the current, i would guess 20 times the currnet(10 amps) would give a pull of 600 pounds. I would not worry about passing 20 amps for a short period (say ten minutes) which would lift a engine block (if the mating surfaces were intimate).
If I wanted a 1 to 1 isolation ttransformer, i would disassemble the other tranformer and mount both windings on the same leg and re-install the "I " Piece (and maybe the shunts). The result would be a 1 to 2 kw isolation transformer, which on a home made EDM (one of those using lamps for current limiting), would prevent shocks. The use of direct line currnet to the homemade EDM is unsafe and has been rightly critized.
As a side note, I have a battery charger (for motorhome) that makes 60 amps for a long time (long enough to over heat the batteries) in a package maybe 5 inches by five inches by eight inches. The "12 volt winding" (acutualy more like 18 volts RMS) consists of about 15 turns of number 8 wire, wound on a insulation core of fish paper and expoy dipped (painted really) to keep the wires from moving and shorting. Surplus 200 amp rectifiers (4 each, hooked in bridge formation) and a computer power supply fan for cooling the heat sinked rectifiers). The rig probably weighs less than 10 pounds and will jump start my engine with only a few seconds charge to the battery. For trickle chrages i use a variac to control the voltage, but thats another story.
Hope this encourages thosewho wanted a strong electro magnet at low cost.