VA rating for an Iron Core transformer

[still4given]

Hi Guys

Is that a semi easy way to estimate the VA rating of an iron core transformer. I have a few that were salvaged from discarded amps.

Thanks, Terry

 

[audiostrat]

There is a general rule of thumb for EI cores, based on their dimensions. For toroidal cores, I don't know.

I have seen a graph inside a book. I may search it when I find time. 🙂

 

[AndrewT]

Core area in square inches.
VA ~ 31 * [core area]² when flux is 1T.

 

[ingenieus]

I would measure the dimensions and output voltages and look for something similar in a catalog of currently available transformers. Not very scientific, I know.

 

[Mark Johnson]

In a different thread, (this post) presented some data showing an excellent correlation between weight and VA rating - at least, among different transformers in a single product line from a single manufacturer. I copied its plot below. You could add more datapoints from other mfrs and other bobbin arrangements, if you wanted to get a feel for the variability of the relationship.

 

[Elvee]

There are methods, based on size, weight, primary resistance, etc.
Have a look here: http://www.diyaudio.com/forums/parts/175677-guessing-power-transformer.html
Obviously, they are always approximate, because you have no way of guessing the insulation class, or the quality of the materials and other factors.
In those conditions, it is better to stay on the safe side.

 

[TonyTecson]

from RDH4,

VA =(5.58 x A)^2
where A = core area in square inches, center leg x stacking height x stacking factor, (0.9 to 0.95)

note that results are at best estimates, power capacity really depends on how hot you are willing to work your traffos on...