Calculating Primary and Secondary Transformer Windings

Vs/Vp=Ns/Np

you have 240v in your house, some of the lights are only 12v downlighters, so you need a transformer! If there are 1000 primery turns, how meny secondary turns would the transformer have?

the volages in the windings ie. voltage ratio...N1/N2=V1/V2

when splitting voltage, the amps are affected how?

what is the formula for amps in a transformer system, what should one expect the output amps to be?

The output amps will be determined by the load. The transformer has to be sized so as to accomodate the load current at the outpur voltage. Transformers are typically quoted as ??VA; this shows the maximum amount of power that the transformer can transform in the long term without deterioration or failure. Protection against overcurrent could be by fuses or overcurrent circuit breakers, for example.

Ok, thanks PW.

Let me rephrase that, how much extra VAs can one expect from submersion of tranformer in oil?

I'm not sure what you're looking for, so here's a sort of long answer.

Assume a sinusoid voltage. For other shapes, you have to use a Fourier series or a "tried and true" formula.

The number of turns N = Vrms X 10⁸/4.44BfA_eff where B is the operating point of the core material in Gauss, f is the frequency in Hz, and Aeff is the effective cross-sectional area of the core.

B can be obtained from a magnetization curve for the core material. You need to stay below saturation and many people will develop a rule of thumb like 0.9 of saturation, or 0.85, depending on how they want to limit core losses and/or allow for over-voltage. The core manufacturer will supply those curves as well as loss curves.

The effective cross-sectional area is a function of how the core is made. In a powder core, you will need to consult the manufacturer's data sheet. For stamped laminations, you generally use a stacking factor that accounts for coating on the lamination and the slight burr produced by stamping which keeps laminations from lying perfectly coincident. The stacking factor will typically be in the 0.85 to 0.95 range, but that also depends on size.

Frequency is obvious.

Now, there will be a primary current which is proportional to the secondary current plus some current to cover losses (heat) in the core. There will be an IR drop from those currents and that will decrease the primary voltage slightly. I am greatly simplifying this explanation since you are starting out. Later, you can look at equivalent circuits.

Likewise on the secondary side, there will be some voltage loss. The result of this is that the ideal ratio N_s/N_p will only be about 98% realized. If you are only, say, a freshman college student, you can probably just ignore all that loss stuff. If you are a working engineer, you need more detail.

A good link to understand more is

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/tracir.html

Tom

Different transformer has different calculation method. but allof them have positive ration relationship betwennt voltage and turns.

the key is you hve to calculate the primary turns then you can get the second easily.

The primary depends on work way, but you seem to get general use transformer. you can use one who give you above to get it.'

you can also search the forum, there were many answers in the past threads post here.