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# 3VA transformer, making sure I got things right ;)

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#### csdave

##### Member level 5
Hi all,
I just need to make sure I am not mistaken.
If I have a 6v 3VA transformer, then the maximum current it gives me is 500mA because the 6V are rms and not peak, right?

Yes.

However, don´t forget in some applications you must consider Power Factor (PF) wich may reduce a little bit effective power.

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The only thing that limits the current is the resistance of the windings. If you put a short circuit on the output of the transformer, it will supply a lot of amps and go up in smoke. The current drawn from the transformer depends on the load you put on it.

Transformers are rated by temperature rise, what power they can continuously supply without exceeding a maximum temperature. I believe the maximum temperature is 70 degrees C.

So a 6 volt secondary transformer rated at 3 VA will be able to supply 500mA continuously without overheating and melting.

The only thing that limits the current is the resistance of the windings....

There exists another source of heating, very important.
That´s magnetic flow saturation.

If total power conducted by transformer exceeds nominal specified value, nagnectic histeresis reaches beyond the abillity to disssipate and overheat. In some cases, that phenomen affects much more than those at windings.
To solve the problem, can reduce input power or increase coil size.

For main AC with frequency in range of 50/60Hz, the core size can be obtained by simple formula bellow :
Ae = SQUARE_ROOT ( P )
Ae = Effective area of cross section of transformer[cm]
P = Power [watts]

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There exists another source of heating, very important.
That´s magnetic flow saturation.

If total power conducted by transformer exceeds nominal specified value, nagnectic histeresis reaches beyond the abillity to disssipate and overheat. In some cases, that phenomen affects much more than those at windings.
To solve the problem, can reduce input power or increase coil size.

For main AC with frequency in range of 50/60Hz, the core size can be obtained by simple formula bellow :

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Interesting! Still if I stay within 500mA I'm fine, right?

Generally power specified value is compatible to coil size.
You should measure to certify but there is no need if core is not heat.

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Interesting! Still if I stay within 500mA I'm fine, right?

Seems to me there's a lot of fuss being made over such a simple thing.

Yes, you are right. Ignore all the dust which is flying around ....

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