RE: [CAD_CAM_EDM_DRO] 28v power transformer

Glad to hear it works.

I hope the way you did it was "just the way I said", BUT modified per the
corrections from Roy & theowyn.
If not, you got lucky. Either way, I apologize for giving you the wrong info
at first.

Just to make sure that the RIGHT info is out there, in one place, here's a
rewrite of my original message.

>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 fight each other and cause

a large primary current to flow, even with no load on the secondary, which
will blow a fuse or breaker(hopefully), or destroy either the transformer
or some other part of the circuit(not recommended).

This can be done as follows:

There will be 4 wires coming out of the primary side. The first task is to
identify which pairs are parts of the same windings. Take an ohmmeter and
measure for continuity between any two wires. If you get a
"less-than-infinite"
reading, you've found pair #1! If the reading is infinite ohms, swap one of
the
wires for an unused one.Keep doing this until you get a continuity reading,
and
mark these leads 1A & 1B. At this point, you should bee able to see
continuity
between the 2 remaining wires; check it, and if so, mark these 2A & 2B.
Finally,
make sure you have "infinite ohms" between:
1A and 2A
1A and 2B
2A and 1B
If you don't, then this transformer does NOT have dual primary windings, and
further
Detective work will be necessary in order to figure out how to use it.

Assuming that there ARE 2 separate primary windings, the next step is to
connect
leads 1A & 2A together and to the Neutral side of the AC line. Insulate or
otherwise
secure lead 1B, and connect lead 2B to the Hot side of the AC line.

Power up the transformer, and check for the proper(or close to it) AC
voltages on the
secondary side. If all is well, measure the AC volts between primary leads
1B and 2B.
If you get "zero" volts or very close to it, power down, connect 1B to 2B
and to the
Hot side of the AC line, and you're done. If you get 240VAC(or close to it).
Then power
down, connect 1A to 2B to Neutral, and 1B to 2A to Hot, and you're done.

If you get a voltage reading between 1B and 2B that is "not-zero" and
"not-240VAC",
then you may have a transformer that has 2 different primary windings. In
this case,
you will use only one of these windings, and insulate the leads of the other
winding.
Use whichever of the windings gives you the proper voltages on the secondary
side.


Sorry again for the confusion.

Andy Wander
Verrex Corporation


-----Original Message-----
From: Robert Adams [mailto:thinkcnc@...]
Sent: Saturday, April 24, 2004 10:09 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] 28v power transformer

Thanks Andy got it done just the way you said.