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WTB: UK/AUS microwave transformer 240V 50Hz

Marco Polo

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Hi all,

I'm looking to buy one or two microwave transformers designed for the 240v/50Hz mains supply in the UK and Australia. I live in the US and will be running the MOT's on 120v/60Hz, with the idea that core saturation will be less of a problem due to UK/Euro/Aus units having to handle twice as many volt-seconds as their USA counterparts.

I understand that the secondary voltage will be less due to powering with lower supply voltage, but I wasn't planning on messing with high voltage anyway and will probably just remove the HV winding and replace it with a lower voltage/high current one.

I've found a few on the UK eBay and honestly, the price isn't that bad... about £26 ~= 40 dollars shipped international priority. The sellers on the Australian eBay won't ship to the US at all. Given the choice, I'd prefer to buy from another LPF member anyway, before going to eBay. If anyone has a 240v/50Hz MOT or two that they'd like to sell, please let me know.

Thanks,
MP
 



Alaskan

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I used to build high power transmitters with high voltage transformers, would one of those work? If so, what would be the ideal constant current and voltage rating? Constant current meaning 100 percent duty cycle with transformers.
 

vk2fro

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Damn if I had have seen this a bit earlier I could have scruffed the microwave I saw on the street earlier and salvaged the transformer. Most of the time over here its usually the fuse that pops and people just trash the microwave and buy a new one (they are cheap enough). 9 times out of ten the MOT is perfectly fine.

I'll keep an eye out. Postage is going to be painful though, MOTs are quite heavy (you probably already know this).

Provided you exercise proper safety procedures, they are also a tonne of fun to play with :)

I've killed a few in my time overloading them before I wised up and stuck a column heater in series as a ballast :)
 
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Marco Polo

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Damn if I had have seen this a bit earlier I could have scruffed the microwave I saw on the street earlier and salvaged the transformer. Most of the time over here its usually the fuse that pops and people just trash the microwave and buy a new one (they are cheap enough). 9 times out of ten the MOT is perfectly fine.

I'll keep an eye out. Postage is going to be painful though, MOTs are quite heavy (you probably already know this).

Provided you exercise proper safety procedures, they are also a tonne of fun to play with :)

I've killed a few in my time overloading them before I wised up and stuck a column heater in series as a ballast :)
I finally got a MOT from the UK. 45 dollars shipped, doesn't seem too bad. Feasible to get another one if I kill this one or want to do the anti-phase inputs and split-phase secondary thing for twice the volts. The seller didn't pack it worth a damn though, no padding whatsoever. a bit disappointing. The windings appear to be fine but one corner of the core got bent/deformed from hitting something hard. I used a vise to flatten it out a bit so it looks ok.

It's 230V 50Hz, with a variac I have 144V 60Hz, so low idle current. It can arc a bit but not a whole lot. The primary wire is noticeably thinner than 120V primaries, is aluminum, and gets hot quickly when you arc it. I guess that makes sense, a microwave that draws 1200W only needs 5A. Maybe twice that while being misused. It looks too small to have come out of anything much bigger than 1000W though.

I can sometimes trip the 20A breaker if I arc the old Basler Electric MOT long enough, with enough volts and some fan cooling. The UK MOT would be in flames long before anything trips (even at 144V) so I guess that qualifies as a fire hazard.

I would need another one to wire antiphase if I wanted ok arcs but for now I don't have the time. This one could probably make an OK ballast but for now it's mostly just a doorstop, or sometimes a paperweight. I note the shunts are a lot smaller than on a 120V MOT, so maybe the UK cores are smaller because they have enough turns per volt despite 240V 50Hz.

Well, whatever. :) At least it's pretty clear that 120V MOTS (the older ones at least, those made in the USA) can arc as well as a 240V unit, without needing a ballast necessarily. They are "120V" but start to saturate by 90V and handle ~105V if duty cycle is short. It's pointless to over that, although tbh I guess it's a bit pointless to do this kind of thing in the first place. ;) But still something to do if you're bored or want to electrocute something.
 
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kaunak

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I bought a couple 120V MOTS on eBay in the last few years, and the 120V versions were only about $25USD with shipping. I guess the 240V UK versions are slightly more than that on average. I've done a good amount of experimenting with them over the years(120V MOTS) and figured out the best way to get nice arcs from them without burning the windings out too quickly, is to short out the secondary on one 120V MOT and use the secondary-shorted MOT as the ballast for the other 120V MOT which will have a stable 1000W ~500mA output on the secondary. That's about the max you can get from any MOT secondary unless you remove the shunts. Even with the arcing transformer shorted, the primary current is 'only' about 20-21A on the primary and usually won't trip a 15 or 20A breaker in any short amount of time. I've found this to work very well and I can pull a stable arc from the second MOT for about 5 minutes straight without any issues. Of course the MOT will get pretty hot, but it will not start smoking the windings at all and there will be no damage to either transformer. MOTs are tough transformers no doubt. I can't say this would work as well with any two MOTs because of manufacturing differences, but the ones I used were pretty standard and weighed about 10lb each.
 
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