Primary Winding for a transformer and need some help

You won't get 50 - 55 volts and 150 - 160 Amps. 50 V and 150 A represents 7.5 kW which is far more than a microwave transformer can deliver.

A transformer will change the voltage in proportion to the number of turns in the primary and the secondary. If there are 10 times as many turns in the primary than the secondary, the voltage will reduce by 10 times. The current will go up in the same proportion as the voltage goes up.

If you change the turns ratio, you change this proportion.

On a transformer each turn will give you a certain voltage. It will be about 0.5 - 1 V per turn. For a welding transformer where only a small voltage is needed it's quite practical to feed 30 turns around the core. It is much more difficult to wind the primary where many more turns are needed.

The transformer in the image was made by winding the wire around the plastic former, and then assembling the laminations that make up the core. The laminations are then held together by a couple of lines of welding that you can see under the label. There will be two more lines of weld on the bottom.

The only reason that people make welders from microwave oven transformers is that second-hand microwave oven transformers are cheap. If you have to buy the parts new, or wind your own primary windings, it won't be worth it.

If you are using two transformers to increase the power, connect the primaries of both transformers to the mains, so they are in parallel and both supplied at 220 V. Connect the two new 30-turn secondary winding in series, and you will get twice the voltage. If you get a voltage from each secondary, but near zero volts from the two in series, reverse the connections on one of the primary windings or one of the secondary windings.

The lamination does not directly affect the secondary. The lamination is the way that the iron core is made from thin layers of metal. The iron core and the primary winding should not be altered.

To add a little more - putting two transformers in parallel isn't going to double the power anyway, as even with 240V 13A mains (as in the UK) you can't get more than 13A from a mains socket - and a single microwave is probably pushing over half of that anyway.

If you can't get a transformer from an old microwave (which should be easy, there must be thousands thrown away every day), then just buy a new cheap microwave oven, and take the transformer out of that - it will be cheaper than buying a replacement transformer, and probably cheaper than buying a transformer core (if you could find one) and the wire to wind it with.

You need to make sure that your microwave oven isn't an inverter one. You need a microwave oven that is much heavier on one side than the other.

I go to the used appliance store and get a secondhand microwave. I also find then in the metal recycle bens and in the trash. Every country has different words for what I am trying to say, and different ways to handle old appliances no one wants.

Also if using a Microwave version, you will need to drive the magnetic shunt out .
Typically most have them.

Diver300 said:

You need to make sure that your microwave oven isn't an inverter one. You need a microwave oven that is much heavier on one side than the other.

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To be fair they are pretty uncommon, and (as far as I understand?) Panasonic have now discontinued them - too expensive, and too unreliable. Did anyone other than Panasonic ever make them?.

Nigel Goodwin said:

To be fair they are pretty uncommon, and (as far as I understand?) Panasonic have now discontinued them - too expensive, and too unreliable. Did anyone other than Panasonic ever make them?.

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To be honest, I don't know. I tried, and failed, to fix an inverter one a few years ago and the one in my house at the moment a fitted one so I have no idea how heavy it is or where the centre of balance is.

I've seen switch-mode power supplies take over in so many application that I assumed that the same would happen with microwave ovens. However I realise that in some places the mains-frequency transformers are still used for various reasons, such as site transformers and instant heat soldering irons.

Basically they are non-repairable, when they fail you're supposed to replace the entire PSU module - and unfortunately, if the magnetron fails, it normally takes out the PSU as well. As a Panasonic warranty service agent I replaced a number of them (both mag and PSU) under warranty, and I always kept the faulty PSU's - as I couldn't bear to throw them away, and with the hope of perhaps repairing them one day?.

However, the company I worked for closed, and pretty well everything was donated to my friend Michael - including the faulty PSU's.

Funnily enough, the other week I called to see him (we use him as a sub-contractor) and we got talking about the PSU's - as one was on his bench. Apparently, it was one of the ones I'd changed and kept - and Panasonic eventually made repair kits available for repairing them, and at 'reasonable' prices, so bought a load while they still available.

But like I said, Panasonic have now abandoned the idea, it's too expensive, and too unreliable - and all it does it make the oven a bit lighter.