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# reverse calculate of a transformer..!!

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#### ali-libre

##### Junior Member level 1
i have an old transformer i'm know
input 220V
primary count winding =430*1mm wire
secoundary = 4*(52* 2mm) each 24 Vac
another info in this picture

i want to know how to calculate to know output in W

Core EI150a is good for 400 - 450 VA, according to primary wire gauge the transformer can handle 400 VA.

ali-libre

### ali-libre

Points: 2
i want to know how to calculate to know output in W
As stated above, the maximum power is limited by how hot it will get. And that is mostly determined by how much current the wire can carry without overheating.
It should be able to work continuously with about two amps of primary current.

Core EI150a is good for 400 - 450 VA, according to primary wire gauge the transformer can handle 400 VA.
hw did you defind it...?

so, if i make it cool i have more power continusly...?
how do i keep it cool...?

hw did you defind it...?
I'm referring to data in transformer design handbooks. In tells the said VA number and 2.3 A/mm² current density for this core.

The power rating is for regular free convection cooling. You might be able to sligthly increase the power by using forced air cooling, but I don't believe that it pays the effort.

To know the maximum transformer load power, one must combine wire and core loss. A practical method is to connect the transformer to a nominal mains like 220 V AC, and use a high-power resistor combination as a load on the secondary.
One rule says the output voltage may drop by 10 % under a maximum load but the combined core/wire loss may cause overheating after some time.
I used thermistors to monitor core AND wire temperature and let the trasformer with that 10% down load run for at least five hours. If the temperature rises not higher than 60 degrees, the transformer I deem safe. If it tends to rise higher, I can use a small fan to reduce the temperature. But try to keep it all safe, under 60 degrees.
Some modern transformers use green-enamel wire that allows to solder the ends without removing the enamel. Those wires may not be safe at 60 deg.C

ali-libre

### ali-libre

Points: 2
A good wheeze is to use the temperature coefficient of copper to find the internal temperature of a transformer. Its about .38% /deg C.
Frank

ali-libre

Points: 2