Powerful power supply from a microwave transformer
This master class buden is a bit contradictory and will cause more than one scattered opinion. I want to share how to make a powerful rectifier from a transformer with a microwave oven - a power supply unit, for the voltage I need. Very often microwaves fail and are thrown into the garbage bin. I recently broke one more and I decided to give a second life to its transformer. The transformer there is a step-up and usually converts 220 V to high voltage 2000-2500 V, necessary to excite the magnetron. I have seen many people convert these transformers or under the apparatus for resistance welding, or apparatus for arc welding. But I have never seen a powerful power supply unit made of it. After all, a transformer is very powerful, about 900 W, and this is not enough. In general, I will show you how to rewind a transformer to the voltage you need.Usually a microwave transformer contains three windings. The most numerous, wound up with the thinnest wire is an upward, secondary one, at the exit of which is 2000-2500 V. We do not need it, we will remove it. The second winding, thicker, with less wire than the secondary, is a 220-volt mains. Also, between the two massive windings, there is the smallest, which consists of several turns of wire. This is a low-voltage winding of about 6-15 V, giving out the voltage to the magnet of the magnetron.It is necessary to cut down the seams holding "Sh" -shaped plates and "I" -type. The seams of the Chinese manufacturer are not as strong as they seem. They can be cut by a Bulgarian or even chipped with a chisel with hammers. I used a grinder, this is a humane way.Remove all coils. If they are very firmly seated - knock gently with a rubber hammer. only the winding for 220 V is useful, the rest are deleted. We put back the primary winding for 220 V and place it downward of the “W” -shaped core.Certainly not the same, but coiled up on a drum. We estimate the current and volume of the coil. From these values choose the diameter of the wire.I assembled such a simple device for winding a coil. The core itself is made of wood, the plexiglass sidewalls. You can attach it to a drill or screwdriver.Wound, assembled, connected. I measure the output voltage, almost hit - 513 V, which is acceptable for me.After the winding is all taut, put the tightly pressed paper into the holes, after removing the wedges. This is my primitive way. I recommend to impregnate the winding with epoxy, otherwise it will be very humid.After all the windings are fixed, it's time to assemble the transformer core. To do this, we fix the entire structure with a clamp and weld the same places with arc welding as before. To make a thick seam is not necessary, everything should look like it was. Next, for my rectifier I will need:I'll load the rectifier by 20 A,Naturally, the diode bridge must be installed on the radiator. Just like, if you use a metal case like me, do not forget to ground it.
We disassemblemicrowave transformer
Cutting the seams of the magnetic circuit
Calculation of the secondary windingNow we need to calculate the number of turns of the secondary winding. To do this, find out the transformation ratio. Usually, in such transformers it is equal to one, hence one turn of the wire will give out one volt, but this is not always the case and need to be rechecked. We take any wire and wind 10 turns of wire onto the core. Then we collect the core and clamp it with a clamp so that it does not fall apart. Be sure to feed a 220 V fuse to the primary winding. And at this time we measure the voltage at the output of the 10-turn coil. In theory, it should be 10 V. If not, then the transformation ratio is not as usual and you need to make calculations to calculate the voltage for your winding.All this is not difficult, mathematics is the fifth grade. I have two transformers available. One I will do at 500 V, the other at 36 V. You can do at any other voltage.
Winding the transformer coil to 500 VThe transformation ratio of my copy is one to one. And in order to wind a 500 V winding, I need to respectively make 500 turns of a wire on a coil. We take the wire.
36 V transformerYou can wind the 36 W winding manually by taking the appropriate wire.To put and straighten the winding on the core such wedges can be used, see the photo.
Work on bugsI rewound the winding to make it more dense and powerful. For this, I wound it with a double wire, instead of one thick. In the end I will connect them.
About safetyBe careful when connecting a transformer never take your time and double check everything. Connect the transformer only through a fuse to avoid a possible short circuit. Do not touch live parts while the transformer is operating. Also, when processing metal, be careful and use eye protection.
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