Re: Power supply voltage question...more info..

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Russ Waters <mycncworld@y...>
wrote:

> This is a 12 amp supply, and it does have a low voltage winding

(secondary side), I will getting a voltage reading on it tonight.
Bucking? tell me more.....

>
> Russ
>

If the winding is separate (not a tap off of) the secondary you can
wire it basically in series with the primary. All windings have a
start and finish but it's not always obvious and with out a dual
channel scope you can't make an easy determination. When you wire
two windings in series there are two possibilites: one is that you
get them in phase and they add voltages. The other is that they are
out of phase and they "buck". If they are the same voltage output
the net result is zero and lots of current.

If you wire the voltage of the smaller secondary out of phase with
the primary it subtracts that voltage from the AC side. Lets take an
example: Say your transformer is a 32 volt secondary, 120V primary.
That's a 4:1 ratio. Now if you have a 12V auxiliary secondary you
can wire bucking you subtract the 12 from 120 and have 108. At 4:1
the secondary voltage then becomes 27VAC (38.2V DC on the filter).

Don't just start rewiring. Never forget there are lethal voltages
present. Disconnect the bridge and filter and measure the AC volts
out. The aux secondary goes in series with the existing primary and
the AC feed to the outside of the string.

You can get the same effect by wiring the aux winding in series with
the secondary but the current rating of the AUX has to be as much as
the needed current (12A). Using it on the primary only requires it
to be a 3A winding.

It's a good idea to wire up a standard 100W light bulb in series with
the AC line to deal with potential shorts. It should stay dark with
no load on the transformer secondary.

Wire it up one way and measure the secondary voltage. If it's what
you want you can insulate the leads on go about your other projects.
If not just reverse one or the other of the windings and try again.

Use clip leads to your meter and make sure you have a way to turn the
AC off and on easily. KEEP YOUR HANDS AWAY from any wires with the
AC energized.