Re: Transformer question

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:

>
>
> JanRwl@A... wrote:
>
> > In a message dated 12-Jan-01 07:33:25 Central Standard Time,
> > jvicars@c... writes:
> >
> > > Do transformers work on a ratio of input to output, or are they

strictly for

> > > the rated voltages? In other words if I have a 240 to 120 step

down and I

> > > put 120 on the primaries will I get 60 V on the secondaries?

What are the

> > > practical limits to doing what I described? Thanks
> >

(snip)

> > Also, you can NOT try to put 240 V. into a winding rated for 120

V!!! That

>
> Actually, what will happen is the magnetic circuit will saturate,

and the primary

> Jon

Jon is correct. Transformers are designed based on a working flux
density. The core will saturate and current will become extremely
large if the flux density is too high. The material used (usually
steel laminations) will have a specified maximum flux density. The
formula for flux density is:
E X 10(8th)/4.44f X Np X Ae
where E is the applied voltage, f is the frequency of the input, Np
is the number of turns in the primary, and Ae is the core area in
square CM. What all this means is that if you change any of the
parameters you alter the flux density. You can get by with lowering
the top part of the equation or increasing the bottom part of the
equation without ill effects. Raise the top part (applied voltage)
or lower the bottom (primary turns, frequency or core area) and you
get saturation. While there is some margin built in there is not
enough to allow for more that about 10% change. The primary and
secondary currents are determined primarily by wire size.