Power transformer amperage

[slideman82]

I have a couple of PT and I know their's secondary voltage, but no idea of max current... I know its power could be obtained from some formulae from the core size. Do anyone know this calculations? Thanks!

[bob91343]

Look in a transformer catalog for a transformer of similar weight and that will bring you somewhat close to knowing the power capability. Divide that by the voltage and you have current.

A more accurate way would be to pick open the transformer and measure the wire size. Another way is to load the transformer and measure the temperature rise. Heat in a transformer comes from core losses and copper losses. When there is no load, you only have core losses. Typically, copper and core losses are about equal at full load.

[Tony]

from the radio designer's handbook: power = (A*5.5)squared.
A is the cross-section area in square inches, so that is center leg width x depth of stack.

[slideman82]

I think I made those calculations... but got wrong numbers, that's for sure! I was refering to that formulae that includes completly all core's data (height, depth, width)... but I think I'll try again!

[Tony]

no, just the area under the coil.....tounge width x stack height, that is your core area, factor in 0.9 and you're done....

[jrenkin]

Power handling before saturation would have to do with core size, but power is more than just current. It has to do with current and voltage.

The poster asked about current which should have to do with winding wire cross sectional area.

Knowing this he could find the max current the winding could handle. Then he could apply that limit and the core cross sectional area to figure the power it could handle. I think you would want both parameters to be able to spec your transformer appropriately.

[Tony]

yes, that is the idea.....

[BADFLOPPY]

Dear,
I Think there are a variaty of cores and so, calculation from core was not proper. The designer may design at a higher side or lower side flux dencity.

But surely, the current carrying Capacity depending directly on the coil conductor. If you know the voltage of primary & secondary, It is very easy for you. The capacity is limited by the bottleneck criteria.

Just check SWG of the terminal and No of parallel conductor if any. It will determine your Secondary Current Rating.
Now calculate your primary current for that secondary current. Now check the primary coil wire SWG is sufficient or not. If Yes, ur secondary Voltage x Secondary current is the VA Capacity of transformer. and if not, primary current will limit the VA Rating and then Primary voltage x current be the VA of the transformer.

To measure paralling of conductor in the secondary, you may check the coil resistance and fair idea will be achieved.

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Please Note: In Electrical Engg, Transformer Rating is in VA
or KVA but Not in Watt of KW.
For Electronics Plz consider 0.8 as PF for safety.
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Thanks