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

[Sylvia Else]

whenever the windings have significant resistance.

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.

 

[Jamie]

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.

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.

http://webpages.charter.net/jamie_5"

 

[Matt]

I meant "won't". The OP appeared to be thinking in terms of DC style
plug packs, of which some are regulated, as in they provide a more or
less constant voltage regardless of load.

Sylvia.

"Charles" mentioned regulation. Maybe he was thinking DC despite the
subject line. I supposed that maybe AC could be regulated, but on
second thought that doesn't seem to make sense given what I understand
about PWM.

 

[Phil Allison]

"Matt"

"Charles" mentioned regulation.

** Charles is a *mental* retard.

Maybe he was thinking DC despite the subject line.

** Silly to imagine he thinks at all.

I supposed that maybe AC could be regulated,

** But not inside a cheap wall wart.

You scheme to use a wall wart tranny in reverse is not likely to prove
satisfactory.

If you need to do that, then use a * toroidal * type transformer - because
of their very low primary (ie magnetising ) current they CAN be used in
reverse OK.



...... Phil

 

[JosephKK]

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?

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

 

[JosephKK]

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.

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

 

[Phil Allison]

"JosephKK"

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

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

You stinking, trolling, bloody

OXYGEN THIEF !!!




...... Phil

 

[Ben Bradley]

This makes me wonder if your experience is with substation
transformers or pole pigs or what.

The voltage on the primary is determined by the rate of change of flux,
but also has to equal the supply voltage.

Since that flux is linked to the secondary, the secondary sees the same
rate of change of flux, with the voltage on the secondary being related
to the voltage on the primary just by the number of turns.

In the absence of hysteresis losses on the core, flux leakage, and
resistance, this relationship remains true regardless of load.

In the absence of any practical real-life limitations, I am
perfect.

There are of course such losses, but the transformer is designed to
minimise them. The 25% loss suggested by Phil seems extreme.

Phil may even be understating it (which is unusual for Phil).
Wallwarts are made cheap. Using smaller gauge wire and crappy core
causes lower efficiency at rated load (thus it runs warmer and costs
the consumer more electricity to run it), higher no-load voltage and
other bad engineering crap. Actually, I also understand the core is
operated at or near saturation (because it takes fewer turns this way,
thus saving copper wire), which may actually help regulation, but the
wire resistance is so high it hardly makes a difference.

Wallwarts are designed to minimize three things: cost, cost, and
cost.

Of course all that's obsolete now that there are off-line switching
supplies made smaller and cheaper than walwart transformers.

Perhaps the Japanese, and now Chinese, learned as much from Muntz
as they ever did from Deming. It's amazing the USA has survived this
long, we keep giving away all our good ideas.

 

[Sylvia Else]

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

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.

 

[Ben Bradley]

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.

Welcome to Usenet!

 

[JosephKK]

This makes me wonder if your experience is with substation
transformers or pole pigs or what.


In the absence of any practical real-life limitations, I am
perfect.


Phil may even be understating it (which is unusual for Phil).
Wallwarts are made cheap. Using smaller gauge wire and crappy core
causes lower efficiency at rated load (thus it runs warmer and costs
the consumer more electricity to run it), higher no-load voltage and
other bad engineering crap. Actually, I also understand the core is
operated at or near saturation (because it takes fewer turns this way,
thus saving copper wire), which may actually help regulation, but the
wire resistance is so high it hardly makes a difference.

Wallwarts are designed to minimize three things: cost, cost, and
cost.

Of course all that's obsolete now that there are off-line switching
supplies made smaller and cheaper than walwart transformers.

Perhaps the Japanese, and now Chinese, learned as much from Muntz
as they ever did from Deming. It's amazing the USA has survived this
long, we keep giving away all our good ideas.

Speaking of Demming, not only did we give them the best we had, but
American industrialists persisted in refusing to implement those
techniques ourselves for decades.

 

[JosephKK]

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.

I am still taking your measure from my perspective. You are (or
could/should be) doing the same with the many personalities you have
chosen to expose yourself to. Turnabout is fair play.
I do not suffer a fool gladly. It is not nice, it is not pretty, it
is who i am. As a consequence i bark or bite when a more measured
response will be better received.

 

[Sylvia Else]

I am still taking your measure from my perspective. You are (or
could/should be) doing the same with the many personalities you have
chosen to expose yourself to. Turnabout is fair play.
I do not suffer a fool gladly. It is not nice, it is not pretty, it
is who i am. As a consequence i bark or bite when a more measured
response will be better received.

Well, I suppose it's much easier to lay claim to knowledge if you feel
no need to demonstrate the truth of the claim. There are many who think
they're an expert merely because they know the terminology.

Sylvia.

 

[David Lesher]

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

When it's loosely coupled. A good example is the wall wart Ma Bell used
to give ^H^rent you to light up your Princess phone. Open circuit was say
15 volts, but with one phone's lamps, it was 8, etc. Point was, it was
short circuit proof; it could run into same and never get hot.

 

[Eeyore]

The voltage on the primary is determined by the rate of change of flux,
but also has to equal the supply voltage.

Since that flux is linked to the secondary, the secondary sees the same
rate of change of flux, with the voltage on the secondary being related
to the voltage on the primary just by the number of turns.

In the absence of hysteresis losses on the core, flux leakage, and
resistance, this relationship remains true regardless of load.

There are of course such losses, but the transformer is designed to
minimise them. The 25% loss suggested by Phil seems extreme.

I really hope you don't actually practice electronics in the real world.

Graham

 

[Eeyore]

And not just that alone.

I would have expected them not to

Do you think copper is a super-conductor ?

What the hell are you doing here anyway ?

Graham

 

[Eeyore]

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

I suspect the first 7 words suffice.

Graham

 

[Eeyore]

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.

Have you heard of this thing called the Internet and 'search engines' ?

Is your age > 12 btw ?

Graham

 

[Eeyore]

I do not suffer a fool gladly. It is not nice, it is not pretty, it
is who i am.

Personally I think it's 100 % A1.

Those who can't be bothered to learn never will. Sylvia is a classic example of the
crud being turned out by Universtities today. I have this awful feeling she muct have a
Batchelor's degree. It would explain a lot, along with MBAs, 'bankers', politicians
etc.

Graham

 

[Eeyore]

Well, I suppose it's much easier to lay claim to knowledge if you feel
no need to demonstrate the truth of the claim. There are many who think
they're an expert merely because they know the terminology.

As you know NONE of the above, I suggest you go to sci.electronics.basics, althought it
may be a bit over your head.

Graham