Re: [CAD_CAM_EDM_DRO] 28v power transformer

On Wednesday 21 April 2004 01:06 pm, Andy Wander wrote:

> Many power transformers are designed for use on either 120VAC or 240VAC,
> and they are wired differently depending on which voltage you are using.
>
> The basic concept is that there are 2 identical primary windings, and if
> you connect them in series, you then apply 240VAC across the entire series
> length of the 2 coils.
> If you connect them in parallel, you apply 120VAC across "both coils" at
> the same time. The net result is the same output voltage whether "wired
> for/connected to" 120VAC or 240VAC.

> To do this correctly, you must connect the coils in the proper phase
> relationship or polarity, otherwise they will cancel each other out and you
> will get "zero" volts out of the secondary. This can be done by
> trial-and-error, as you are not likely to damage anything by hooking it up
> wrong.

This is correct so far, but...

> So, in your case, just wire the 2 coils in parallel, apply 120VAC across
> the parallel primary coils, and measure for the proper AC voltage at the
> secondary. If you get "zero" or close to it, you should change the polarity
> of ONE of the primary coils, and then try again.

This isn't! First thing I'd suggest in this case is to check with an ohmmeter
to verify that these are indeed two separate primary windings, and not a
single primary winding with a number of taps. If the latter turns out to be
the case, then a completely different approach is going to be needed.

If they are indeed two apparently identical primary windings, the correct
approach is to connect _one_ pair of wires together. Apply line voltage to
one of the windings. Measuring the voltage between the unconnected wire and
the wire of the other winding that's not tied together with the other one
should give near zero volts, while measuring across the unconnected winding
should give line voltage. If that unconnected wire shows near double the
line voltage, then the windings are out of phase with each other.