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

• posted

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 amounts to asking whether there are any 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.
• posted

Sorry, folks. Obviously I made an error.

I meant to ask what voltage I would get at the prongs if I hook low AC voltage to what is normally the output.

BTW 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?

• posted

"Matt"

** Yep - the " other end " will be at a lower voltage.

Think it through.

** No.

** A "wall wart" will reduce 120 volts AC to about 28 volts AC when there is no load - so the winding ratio is 4.3: 1.

The same ratio will apply in reverse, so 24 volts becomes 103 volts with NO load.

..... Phil

• posted

Yes, I goofed when I stated the direction of hookup. I should have asked what happens at the input when I hook low voltage to what is normally the output.

No, there are no other components, or no, the questions are not equivalent?

• posted

Or is just mislabelled. If you assume it's really a 110V transformer, then the output is exactly what you'd expect.

If it's just a transformer you want expect any sort of regulation.

Sylvia.

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Since when is the output voltage of a simple transformer a significant function of load?

Sylvia.

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Sillier than Anyone Else

** Totally absurd CRAP.

...... Phil

• posted

** An AC output wall wart contains ONLY a transformer.

The transformer may have a thermal fuse incorporated in it's primary winding - which makes it part of the transformer.

..... Phil

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" Stupider than ANYONE Else TROLL "

** ROTFLMAO !!!

Wot a hoot !!!!!

Old Mick Faraday is rolling in his grave .....

..... Phil

• posted

Connect a rated load to the output and the voltage will be lower (perhaps even lower than the nameplate 24V).

Perhaps. Throw a 700 mA 24V load (34 ohms, 20 Watt resistor) on its output and measure its output voltage.

```--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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• posted

Both him and Georg Ohm (don't forget the real part of the impedance).

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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• posted

often there's a fuse built into the secondary winding of the transformer. other than that no.

• posted

whenever the windings have significant resistance.

• posted

I would have expected them not to, though some research has indicated that small ones do, presumably on the grounds that the resultant heating is manageable. The core hysteresis losses seem to be of the same order, though it's not immediately clear to me whether they contribute to output voltage droop.

Syliva.

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No one ever heard of split bobbin transformers? can be constructed to deliver a limited current load on the secondary while not exerting the primary. Found a lot in cheap charging systems to reduce cost of other components.

Hence the reason why using a radio shack xformer would not behave in the same manner.

"

• posted

With that label and measurement it does sound like a transformer. What does the output waveform look like?

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NO

It seems no one has taught you about flux losses of small transformers.

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"JosephKK"

** And nobody has told you a damn thing either.

You stinking, trolling, bloody

OXYGEN THIEF !!!

..... Phil

• posted

NO

If you believe that's true, a more helpful response would be some sort of explanation, or a link to one. Comments such as yours make it appear that your primary motivation for posting is to make yourself feel superior.

Sylvia.

• posted

NO

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