want to make 50-0-50 5 ampere mains transformer

[ravslanka]

could any one tell me how to make 50-0-50 5 ampere 230 volt mains transformer on ei core i want to use it an amplifier which needs 70-0-70 rectified dc voltage. it is very expensive in local market please someone help

[AndrewT]

Why 5A?

70-0-70 will allow 200W into 8ohm or 400W into 4ohm.
500VA is too large for the 8ohm and too small for the 4ohm.

[wakibaki]

If you don't know how to design this transformer then it would be better to buy one, as mains voltage is dangerous, and efficient transformer design is not simple.

w

[wg_ski]

Originally posted by wakibaki
If you don't know how to design this transformer then it would be better to buy one, as mains voltage is dangerous, and efficient transformer design is not simple.

w

True, but rewinding a secondary isn't terribly hard. If there is a toroid available cheap with an appropriate VA rating and an intact primary, pull the old secondary off and slap on a new one. It's possible with EI cores, too, but only on ones with plastic bobbins.

Put on 10 turns or so, calculate the volts per turn, then wind the secondary appropriately. 5 amps takes about an 18 gage wire in trafo applications. Multiple identical secondaries should be wound together if possible - keeping in mind that the voltage between turns shouldn't be allowed to get terribly high.

[Tony]

Originally posted by ravslanka
could any one tell me how to make 50-0-50 5 ampere 230 volt mains transformer on ei core i want to use it an amplifier which needs 70-0-70 rectified dc voltage. it is very expensive in local market please someone help

hmmmm...100v ct at 5 amps...i would use an EI 175, 1 3/4 inch core stacked 3inches....apportion 50% for primary and secondary coils...

core is about 7kgs, copper is around 2kgs, and other stuff like fish paper etc...so now if you can compare the price you have to pay for these as against buying a ready made one....you may end up spending more..


if you have no experience in making transformers, better not do this...

[dangus]

Transformer design isn't rocket science. The ARRL Handbook (known as the Radio Amateur's Handbook) had a good explanation with rules of thumb, as did my "Electricity 11" text. I rewound a transformer salvaged from an old tube TV set to use for a power amp I was building (way back in the days of disco). I measured the secondary voltage with the original winding, counted the turns as I removed it, then calculated how many turns to get the voltage I wanted. Wire gauge was based on some rule of thumb like so many "circular mils" of wire area per ampere.

You should be able to find some book(s) in a library that cover the basics of transformers. Or probably on the web someplace by now.

[AndrewT]

how do you ensure the laminations do not short together where the oxide layer has been scraped off during dismantling and reassembly?

Once the EI laminations are off, the wire side is simple. Any school kid can work it out.
But a transformer is a lot more than just copper wire.

[Tony]

in the RDH 3 you will find this: for a primary voltage of 250vac and at 50Hz, primary turns is 1400/A ; where A is the core crossection area times 90%....

i have been usign these to make my transfrmers....

[ravslanka]

thanks for all you guys for suggestions

Originally posted by AndrewT
Why 5A?

70-0-70 will allow 200W into 8ohm or 400W into 4ohm.
500VA is too large for the 8ohm and too small for the 4ohm.

AndrewT
i ill be using it to drive a load of 8 ohm for a stereo version

Originally posted by Tony



hmmmm...100v ct at 5 amps...i would use an EI 175, 1 3/4 inch core stacked 3inches....apportion 50% for primary and secondary coils...

core is about 7kgs, copper is around 2kgs, and other stuff like fish paper etc...so now if you can compare the price you have to pay for these as against buying a ready made one....you may end up spending more..


if you have no experience in making transformers, better not do this...

yes for shure true but the quality of transformers are very cheap
and are very expensive to buy.and no other source except diy.

so tony please tell me what core size,wire gauge ,turns of p/s

[wakibaki]

If you can find a txfrmr with a 5A rating, and a higher voltage output than you need, then just unwind coils from the secondary measuring the voltage until it drops to the required level.

Otherwise pick one with a VA rating slightly higher than you require (for safety). Unwind the secondary counting the turns. Divide the turns by the rated voltage. This gives you the turns per volt. Calculate the new turns number required. Rewind with 5A wire or better, taking care to follow the original wiring scheme and replacing any paper or other insulating layers. Take care when winding not to damage the wire insulation against any sharp corners. You can find the wire gage thru google.

Warning! Danger of death. Transformers can be dangerous. You have been warned.

w