Re: Using an AC-to-AC wall wart transformer/adapter in reverse


"Matt" <matt@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
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Ralph Mowery wrote:
"Matt" <matt@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
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Suppose I have a plug-in transformer that reduces 120VAC power to some
lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the
reverse---increase a low-voltage source back up to 120VAC.

Would there be a problem in connecting the low-voltage power to the
plug-in prongs of the wall wart (instead of the normal use: plugging the
prongs into the wall outlet) and expecting to get high-voltage power
back out the other end?

I guess my question is answered if I know that there are no components
other than the transformer inside the wall wart.

My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or
24VAC) to convert 24VAC back up to 120VAC.

If it is an AC output and not a DC output wall wart then you can connect
12 volts to it and get out about 120 volts if it is normally a 12 volt
output. Just put the 12 volts to the normal 12 volt output and the prongs
will have 120 volts on them . You have to check to see how much current
or how many watts the transformer is rated for as not to overload it. If
your wall wart is good for 12 volts at one amp, then about all you can
draw at 120 volts is 1/10 of an amp.

Usuallly transformers do not care if they are connected up either way.
Sometimes the output voltage will exceed the insulation of the wiring.


Thanks.

I am measuring about 25.7 VAC at the output when the input is 117.5 VAC.

The thing is labeled "Plug-in class 2 transformer, Input: AC 120V 60Hz
35W, Output: AC 24VCT 700 mA".

So it is producing well over its nominal voltage. Can I conclude that it
is unregulated---that it is just a plain old transformer?

Can I expect the same _power_ capabilities in normal and reverse
direction? Your remark about current seems to indicate that.

It has a 3-prong (grounded) plug. What could that tell somebody about its
innards?
It is not likely anything except a transformer and transformers basically
work either way. There are some ratio and loss effects as AZ Nomad noted so
your actual voltage output will be a little less than what you might expect.
If you supply the low voltage winding with 24 VAC you should be able to get
about 0.14A from the high voltage winding at a high enough voltage to
operate a nominal 110-120V device. Monitor the temperature to be sure it is
not overloaded.

The three prong grounded plug does not tell anything relevant about it.

Don Young



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Relevant Pages

  • Re: Using an AC-to-AC wall wart transformer/adapter in reverse
    ... other than the transformer inside the wall wart. ... 12 volts to it and get out about 120 volts if it is normally a 12 volt ... watts the transformer is rated for as not to overload it. ... Sometimes the output voltage will exceed the insulation of the wiring. ...
    (alt.home.repair)
  • Re: Using an AC-to-AC wall wart transformer/adapter in reverse
    ... Would there be a problem in connecting the low-voltage power to the ... plug-in prongs of the wall wart (instead of the normal use: ... other than the transformer inside the wall wart. ... I meant to ask what voltage I would get at the prongs if I hook low AC ...
    (sci.electronics.design)
  • Re: Using an AC-to-AC wall wart transformer/adapter in reverse
    ... Would there be a problem in connecting the low-voltage power to the ... plug-in prongs of the wall wart (instead of the normal use: ... other than the transformer inside the wall wart. ... I meant to ask what voltage I would get at the prongs if I hook low AC ...
    (sci.electronics.design)
  • Re: Using an AC-to-AC wall wart transformer/adapter in reverse
    ... Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart and expecting to get high-voltage power back out the other end? ... I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. ... I meant to ask what voltage I would get at the prongs if I hook low AC voltage to what is normally the output. ...
    (alt.home.repair)
  • Re: Using an AC-to-AC wall wart transformer/adapter in reverse
    ... Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart and expecting to get high-voltage power back out the other end? ... I guess my question amounts to asking whether there are any components other than the transformer inside the wall wart. ... I meant to ask what voltage I would get at the prongs if I hook low AC voltage to what is normally the output. ...
    (sci.electronics.design)
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