Heavy Lift Electromagnet from Microwave Oven Transformers

It’s OK, you can admit it — from the time you first saw those huge electromagnetic cranes in scrap yards you’ve wanted to have one. While it may not fling around a car, parts donated from scrapped microwaves can let you build your own electromagnetic lifting device and make that dream finally come true.

We recently watched [MakeItExtreme] turn a couple of microwave oven transformers into a somewhat ill-advised wall-climbing rig. It looks like that may have been the inspiration for this build, and the finished product appears to be a tad more useful this time. The frames of three MOTs are cut open to remove the secondary coils and leave the cores exposed as poles for the future magnets. A shallow dish is fabricated out of steel and the magnets are welded in place.

With the primaries wired together, the magnets are epoxy potted, the business end is faced off cleanly, and the whole thing put to the test. [MakeItExtreme] doesn’t go into control details in the video below, but the website mentions the magnet being powered off a 24V 15A power supply with battery backup in case of mains failure.

They’ve lifted 200kg so far, and it looks like a pretty cool addition to a shop already packed with other builds, like their MOT spot welder and a propane tank sandblaster.

27 thoughts on “Heavy Lift Electromagnet from Microwave Oven Transformers

    1. I bet the copper coil weighed as much as the car.

      It’s not easy to get that many amp-turns out of such a feeble source. You can wind arbitrarily many turns in a coil and create ridiculous magnetic fields, but the series resistance grows to the point that adding more turns decreases the current and diminishes the field.

    2. If I remember right Edmund sold a one ton lift magnet that would work with one dry cell. It was about 3 to 4 inches in diameter and half as thick with a single piece of iron with a circular groove for the coil. I saw a similar magnet lift a car at the Museum of Science and Industry in Chicago decades ago. The trick is perfect flat coupling to a thick flat piece on the load.

  1. I love the concept and the build. But does potting with epoxy resin have enough strength to hold magnets in place? I did not see any mechanical fastners holding magnets in place . If epoxy cracks I see magnets pulling out of metal bracket and failure .Over to someone with engineering experience please.

    1. I’ll try and keep this short and simple.

      The MOT cores are welded to the head, so they’re not coming loose without shearing. The sole purpose of the epoxy would be to keep the coils mounted to the cores (as well as keeping them free of damaging debris that would short the coils.) The only force the epoxy sees is from the eddy currents trying to push the coils away from the core (or vice-versa.) That energy then becomes the electromagnetic force that gets “transferred” to the ferrous cores – that are welded to the head. Since the force from the eddy current is fairly weak, there’s an low extremely low risk for such a failure. Not impossible, but it would take a catastrophic failure.

    1. Dude routinely welds wearing shorts and flip flops. He’s also known to weld quite a bit of galvanized steel, as he does in this video with the lifting ring. Not saying he should do any of this, but there it is.

  2. Anyone know a good source of information for dummies on electromagnet math? I’d love to build one of those electro magnetic pan brakes, but blindly connecting 240VAC to a coil scares me.

    1. They do not connect 240VAC , they connect 24v DC with a 15A source. Remeber AC is a sine signal, you don’t want a signal that turn off 60 or 50 times per second.

        1. One possibility (on contactors) is to have a split pole with a copper ring one one half. This is similar to a shaded pole motor. The current which is induced in the copper ring (shorted winding) is out of phase with the current in the main winding and smooths out the zero crossings. Another possibility, mostly used on valves, is to rely on the inertia of the core, here the dampening effect of the fluid also helps. The device is just not fast enough to follow the 100Hz (or 120Hz in some oversea countries) ripple.

  3. ​So if I am looking to make the magnet more powerful, other than supplying more current, could I wire the primary and secondary coils of the microwave transformer together in series to get more turns (being mindful to keep the direction the current flows the same in both coils)? My thoughts are that it would increase the resistance a bit from the added wire but that the magnet would have a lot more turns. Am I missing something or am I onto something? Thanks in advance!

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