Re: Center tapped transformer

--- In CAD_CAM_EDM_DRO@y..., "Raymond Heckert" <jnr@a...> wrote:

> Tim, You should expect double the amperage at half the
> voltage, if you can split the center tap secondary into two
> isolated windings and use a FWB. Just connect the start to
> start & finish to finish on the secondary. Even if this is
> bi-filar wound (not real likely), the voltage is low
> enough, not to worry about breaking down the wire
> insulation.
>
> RayHex
>

How would that be different than grounding the center tap and using
two diodes? Using the centertap approach, each side of the winding
supplies half of the power. "Watts is watts". Transformers are
designed to transmit power. The total amount of power is determined
by the amount of power (I*E) coupled from the primary to the
secondary through the magnetic field less any losses in the core and
windings. With a given size and type of magnetic core and a given
number of turns in the primary of a fixed wire size, you can only get
a defined number of watts from the secondary. The ratios of voltage
to current change, but to maintain the same load on the transformer,
the total wattage has to remain the same.

In a common center tap configuration the positive section of the sine
wave is transformed by one half of the winding and rectified by one
of the diodes. During the negative transition of the wave the other
half of the winding does positive in relation to the center tap and
performs the other half of the rectification process. You end up
with each side supplying 50% of the average current at half of the
full winding voltage. This maintains the basic total wattage
concept. Since heating and losses in a conductor are a factor of
resistance AND duty cycle, each conductor carrying 2X the current for
1/2 the time is equal to two parallel windings carrying 1X the
current for 100% of the time. There are some other minor factors
that do not make the two methods EXACTLY equal but they are on the
order of 1% or less. Power transformers are not precision devices
anyway. To get the lower voltage,technically you could use just the
center tap and one leg into a full wave bridge and keep PRIMARY
wattage the same, but your secondary winding losses would go up and
depending on the wire size of the secondary might start to overheat.
(Remember that the losses are I^2 * R) Average losses (heat)are
factored over time.