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I used a 900 watt microwave oven transformer to build this with a 48 volts secondary. I decided since I only need 36 turns of wire I would not take the welded laminations apart. I could have removed the welds in the milling machine but I think it will be more work than fishing the wire around and around through the 2 holes.

I tested the house voltage it is 122 VAC.

I tested the microwave oven transformer my Amp Clamp reads 10 Amp idle current with no load on the 2000 VAC secondary coil. This seems high?

Idle current is high 122 x 10 = 1220 watts.

I cut the secondary winding off with the milling machine then drill through the holes with a .500" drill. I pulled what was left of the secondary winding out with plyers.

There are 89 turns of wire on the microwave oven primary. It is an open winding with 9 layers and 10 turns on each layer except for the very last layer it as 9 turns. Core area on this transformer is 3.3984 sq inches.

I did the math several times just to double check to see how many turns should be on the primary but I kept making math errors. One time the math said the primary needs 2 turns. Another time in was over 8000 turns. I tried one more time got a goofy answer so I guit.

Next, with an 89 turn primary on 120 VAC the secondary winding of 48 VAC needs to be 35.6 turns with a center tap. That is 18 turns for 24 volts each side of the center tap.

I put 10 turns on the secondary then tested the transformer With 120 VAC on the primary I get 9 volts on the 10 turn secondary. A added 1 turn at a time and checked it again each time 13 turns gave me 12 volts. I figure I need 13 more turns to get 24 volts but 26 turns gives me 25 volts. Remove 1 turn it gives me 24 VAC.

I have 2 secondary windings each with 25 turns of #14 enamel coated copper wire that tests 24 VAC each. Perfect.

I varnished the windings and let it dry over night. I had to make 3 terminals to glue to the fiberglass tape then wrapped it with more fiberglass tape. I soldered both center taps to the center terminal and the other 2 wires to the other 2 terminals varnished it and let it dry.

I tested each 24 volt winding each one reads 24 VAC. I tested both windings in series and it reads 50 VAC. How can that be??? I test it again with a different volt meter and I still get 24 VAC + 24 VAC = 50 VAC. How is that possible???

Amp clamp still reads 10 amp idle current on the primary like before nothing has changed.

I removed the transformer shuts current is now up to 12 amps on the primary and the secondary voltage is up from 50 to 54 volts.

Secondary winding 10 turns = 9 volts, 13 turns = 12 volts, 25 turns = 24 volts, 50 turns = 50 volts.

I have built a lot of transformers in the past, they all worked. This one is weird. Probably because I did not change the primary winding.

Here are the pictures.

http://i43.photobucket.com/albums/e358/gary350/T1.jpg

http://i43.photobucket.com/albums/e358/gary350/T2.jpg

http://i43.photobucket.com/albums/e358/gary350/T3.jpg

http://i43.photobucket.com/albums/e358/gary350/T4.jpg

http://i43.photobucket.com/albums/e358/gary350/T5.jpg

http://i43.photobucket.com/albums/e358/gary350/T6.jpg

http://i43.photobucket.com/albums/e358/gary350/T7.jpg

I tested the house voltage it is 122 VAC.

I tested the microwave oven transformer my Amp Clamp reads 10 Amp idle current with no load on the 2000 VAC secondary coil. This seems high?

Idle current is high 122 x 10 = 1220 watts.

I cut the secondary winding off with the milling machine then drill through the holes with a .500" drill. I pulled what was left of the secondary winding out with plyers.

There are 89 turns of wire on the microwave oven primary. It is an open winding with 9 layers and 10 turns on each layer except for the very last layer it as 9 turns. Core area on this transformer is 3.3984 sq inches.

I did the math several times just to double check to see how many turns should be on the primary but I kept making math errors. One time the math said the primary needs 2 turns. Another time in was over 8000 turns. I tried one more time got a goofy answer so I guit.

Next, with an 89 turn primary on 120 VAC the secondary winding of 48 VAC needs to be 35.6 turns with a center tap. That is 18 turns for 24 volts each side of the center tap.

I put 10 turns on the secondary then tested the transformer With 120 VAC on the primary I get 9 volts on the 10 turn secondary. A added 1 turn at a time and checked it again each time 13 turns gave me 12 volts. I figure I need 13 more turns to get 24 volts but 26 turns gives me 25 volts. Remove 1 turn it gives me 24 VAC.

I have 2 secondary windings each with 25 turns of #14 enamel coated copper wire that tests 24 VAC each. Perfect.

I varnished the windings and let it dry over night. I had to make 3 terminals to glue to the fiberglass tape then wrapped it with more fiberglass tape. I soldered both center taps to the center terminal and the other 2 wires to the other 2 terminals varnished it and let it dry.

I tested each 24 volt winding each one reads 24 VAC. I tested both windings in series and it reads 50 VAC. How can that be??? I test it again with a different volt meter and I still get 24 VAC + 24 VAC = 50 VAC. How is that possible???

Amp clamp still reads 10 amp idle current on the primary like before nothing has changed.

I removed the transformer shuts current is now up to 12 amps on the primary and the secondary voltage is up from 50 to 54 volts.

Secondary winding 10 turns = 9 volts, 13 turns = 12 volts, 25 turns = 24 volts, 50 turns = 50 volts.

I have built a lot of transformers in the past, they all worked. This one is weird. Probably because I did not change the primary winding.

Here are the pictures.

http://i43.photobucket.com/albums/e358/gary350/T1.jpg

http://i43.photobucket.com/albums/e358/gary350/T2.jpg

http://i43.photobucket.com/albums/e358/gary350/T3.jpg

http://i43.photobucket.com/albums/e358/gary350/T4.jpg

http://i43.photobucket.com/albums/e358/gary350/T5.jpg

http://i43.photobucket.com/albums/e358/gary350/T6.jpg

http://i43.photobucket.com/albums/e358/gary350/T7.jpg

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