Re: [CAD_CAM_EDM_DRO] Power supply question.....

He said 28 & 32 volts, not ohms. Anyways, the transformer as described is
definitely not center-tapped. Not very likely you'd see a 2:1 difference
in dcR. (Maybe 1.2:1). However, if the circuit requirements are really
critical, then Bi-Filar is the way to go (unless you're talking about real
high voltages or frequencies). That way dcR's are virtually identical.

RayHex

----------

> From: Jon Elson <elson@...>
>
> Raymond Heckert wrote:
>
> > If you have only 3 wires on the secondary, and get 28v from start

wire to

> > the tap, and 32v from start to finish, then it's not a ct

(center-tapped)

> > transformer, just a tapped transformer. If there are 5 wires, then

it's

> > probably a tapped bi-filar, with a common center-tap. That's all I

can

> > surmise from your description.
>
> Not always true. If a true CT winding (ie equal number of turns from CT

to

> each end) is wound with one half out to CT, then other half wound on top,

the

> second half will have MUCH higher DC resistance than the first half,

because

> the circumference of the outer winding layers is larger. This is VERY

common

> practice in power transformers, and has minimal effect on the power

supply.

> But, it can be VERY confusing when you see a 2:1 difference in the DC
> resistance, but the AC voltage output from each half of the winding is

the

> same.
>
> Jon