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Forum Index : Electronics : microwave oven transformers
| Author | Message | ||||
| isochronic Guru  Joined: 21/01/2012 Location: AustraliaPosts: 689 |
Any use for old microwave oven transformers ? (6 Kg !) I gather that in their installed state they are hazardous and designed for saving weight etc - one side of the high voltage is connected as a earth-return, and the mains coil is such that the core is saturated and there is a large overcurrent and subsequent cooling fan. Reuse looks like often cutting off the HV coil as a start...but that would still leave beyond-saturation current. Maybe if two are connected is series the increased inductance means they would not saturate, but would there still be realistic output with rewound secondary coils ? Is it worth it ? I guess to do it properly, both coils would have to rewound to be practical. |
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| Pete Locke Senior Member  Joined: 26/06/2013 Location: New ZealandPosts: 181 |
I have two. Great hold down weights when building model air craft weights  |
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| isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689 |
I thought taking one to pieces would mean cutting the windings, but it turned out to be OK and quite easy. There are two welds holding the E-core and I-sections together. After a small surface cut in one weld with a hacksaw there was an audible crack as the rest of the weld snapped. The I-section then rotated off with a little effort, breaking the other weld in the process. The main input winding removes OK with a little leverage. There are two magnetic shunts underneath it about half centimetre thick, then a winding for the magnetron filament I think - about three turns, lifting out easily. The input winding is about 260 - 280 windings at first glance and approx 1.5 ohm according to a cheapie meter (probably not very accurate). The main HV output winding needed a lot more pressure to remove. Eventually I stood on the exposed windings one side at a time, with some padding to avoid damage, and the winding slowly slid off. The DC resistance of the HV winding looks like about 80 ohm, hopefully it is not damaged, it looks ok so far. Here are the laminate blocks and main windings, there are also two small magnetic shunts which may be useful I guess.  I wonder what sort of inverter it would make - probably inefficient and heavy, but very cheap  |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I have rewound several, one as a test transformer for inverter PCBs and the other for dual bench power supply. By taking off the HV windings with cutting disk on a grinder I wound it with the core in tack. It was easy enough to the 20 something turns required. My bench supply has 2 isolated 3A 30VDC outputs, the MOT is well and truly able to supply that. They are definitely useful. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 513 |
The problem is the welded laminates.. it creates excess eddy currents... I think it works !! |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 202 |
http://www.makeitextreme.com/en/newsroom/entry/VIDEOS/electromagnet |
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| isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689 |
It says three in an electromagnet will lift 200kg !!! I am cautious about lifting / manipulating 6 kg, and then only briefly for a short time per day - had a disc/pinched nerve prob some years ago, I am definitely not going there again, it comes back if I so much as sleep in the wrong position for a few times..so I do stuff in small visits. anyway re the eddy currents - it is a good point. A microwave oven is a very specific design and use though, I think it is probably best described as a saturated choke with the excess field running the incorporated output transformer, instead of an ordinary transformer (?). I think it is designed to run giving some regulation effect to cope with varying power voltages, depending on the magnetron absorbing excess/designed power. The mirror-image design means the welds don't encircle much flux though, mostly field leakage. The bench twin supply looks a good idea, might have a bash at that  |
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poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1419 |
uses for a microwave oven transformer: https://www.youtube.com/watch?v=26Dj-4k1TT4 https://www.youtube.com/watch?v=WSgRS0q5lek https://www.youtube.com/watch?v=4bQuFQ5BOtA wronger than a phone book full of wrong phone numbers |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
LOL, love the last one. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You can get a lot more serious with high current using an Aerosharp toroid with 2-3 turns off welding wire as the secondary. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
There is a microformer article online using two microwave transformers to send power long distances. Sounds like it would be nice for hydro. They remove the shorting bars and add a couple extra turns to the primary. They stuff it in a can of oil and +1,000V is sent over a single small wire with ground as the return. |
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