Hi Steve,
Somewhere here, I think you are misunderstanding what is being said.
The OP wanted to put 120V into a secondary that was rated for 60V
and hoped for 240V out of the original 120V primary. This is running
the transformer at 2x its rated voltage... and as has been said over
and over again, this is not a good idea, and will likely result
in the destruction of the transformer.
What the article you are quoting is saying is that transformers work
in a reciprocal way, which is always true... The transformer knows
nothing of which is its primary or secondary winding.
However, the designer of smaller transformers will often add turns
to secondary windings so as to compensate for the voltage drop due
to resistance in the primary and secondary windings... Something
that I stated, and got beat up over, in a thread a month or so ago,
when I stated that you shouldn't parallel dissimilar current,
filament windings.
The only "maybe" that exists in the OP's transformer is maybe it is
really a 240V to 110V transformer that was being used as a 120V to
60V transformer... maybe. A simple experiment is the easiest
way to tell. Put a 50W light bulb in series with the intended primary
and connect it to 120V and if the light bulb is dark, you are probably
fine. If the light bulb lights, forget about this idea.
There can be no new revelations in this thread. The only "aha!"s
will have to be those of readers taking the time to read, confirm,
and finally understand what has been said by the few of us here
who have actually learned the art of transformer design.
-Chuck
Steve wrote:
Sheesh!!
There are no absolutes here, in machine design industries
reverse connecting distribution dry type transformers is commonly
done. Of course allowing for certain limitations.
Here's a quote from Acme Transformers FAQ...
http://www.acmepowerdist.com/ael10.html
7) Can Acme transformers be reverse connected?
ACME dry type Distribution transformers can be reverse connected
without a loss of KVA rating, but there are certain limitations.
Transformers rated 1 KVA and larger single phase, 15 KVA and larger
three phase can be reverse connected without any adverse affects or
loss in KVA capacity. The reason for this limitation in KVA size is,
the turns ratio is the same as the voltage ratio. Example: A
transformer with a 480 volt input, 240 volt output - can have the
output connected to a 240 volt source and thereby become the primary
or input to the transformer, then the original 480 volt primary
winding will become the output or 480 volt secondary. On transformers
rated below 1 KVA single phase there is a turns ratio compensation on
the low voltage winding. This means the low voltage winding has a
greater voltage than the nameplate voltage indicates at no load. For
example, a small single phase transformer having a nameplate voltage
of 480 volts primary and 240 volts secondary, would actually have a no
load voltage of approximately 250 volts, and a full load voltage of
240 volts. If the 240 volt winding were connected to a 240 volt
source, then the output voltage would consequently be approximately
460 volts at no load and approximately 442 volts at full load. As the
KVA becomes smaller, the compensation is greater- resulting in lower
output voltages. When one attempts to use these transformers in
reverse the transformer will not be harmed; however, the output
voltage will be lower than is indicated by the nameplate.
So the correct answer without having a part number or specs on
the transformer is "maybe".
Steve
On Thu, 10 Jul 2003 11:00:34 +1000, Patrick Turner
wrote:
Casino wrote:
Hi All,
I have a step-down power transformer with a 120-volt primary and
60-volt center tapped (30-0-30) secondary. I was wondering if I could
reverse the transformer by plugging-in the 60-volt secondary into the
AC outlet and use it as a step-up for 240-volts? Theoretically, it is
possible, but I'm not sure if it's actually safe to do so.
DO NOT DO THIS.
The transformer will probably hum loudly, and get hot, and perhaps burst
into flame
after awhile. eventually, a thermal fus, if fitted, will blow, and
when the insulation burns off the wires, a short will blow a mains fuse.
This is the result of saturation..
Also, when I travel Europe, can the 120-volt primary be plugged into
240-volts to supply the 120 (117) for North American appliances.
Thanks,
ABSOLUTELY NOT!
Patrick Turner.
C.W.