Phil, isn't this a bit of irony since I clearly asked for something
specific
** And impossible.
Apparently not, because plenty of products out there use wall warts,
are you suggesting they all have to build prototypes for even a simple
AC-DC wall wart? You gave a figure of 0.5 to 0.7 times the rating but
clearly darn near every wart here (quite a big box full) don't adhere
to this, they're all using transformers smaller than your suggestion
would imply and they aren't all bursting into flames or melting
things.
Cos you know NOTHING about the topic - fuckhead.
Phil, how do I put it so you understand?
** Do not ever try that shit on - fuckhead.
You need a pet Phil, or something. If we were in church then the
cursing might seem dramatic but on usenet does it really have any
useful purpose? I suppose you're trying to incite me to call you a
fuckhead too. Will it make you happy, can we move on then or will you
still be stewing for no good reason? I suspect the latter.
This is not a fixed plan for a one-off design Phil, this is a generic
question about transformers.
** You still have not read the whole post - have you ?
Yes
Wasn't it obvious when I replied in a way related to what you had
written throughout the whole post?
What an utter ass you are.
Thank you Phil, but that's not quite enough. You hassle so many
people on usenet that calling me an ass just isn't special or rare
enough to be satisfying.
** You are one, colossally stubborn fool.
Yes, I generally keep at it until I achieve the desired result. I'll
have an equation even if I have to invent one of my own and
experimentally test it. I was just hoping someone out there had more
related info than I did besides generalizations of jumping up in
transformer size to create some margin, which is what I'd been doing
all along and is not so desirable as knowing exactly what that margin
is instead of just a ballpark figure, or at least to get much closer
in accuracy. Even if "use a bigger hammer" is a popular phrase there
has to be a method others are using when they start out with AC
transformer specs, as they manage to produce gear that works fine but
is not rated as high as your conservative estimate suggested would be
necessary. If real world examples and my wanting to find the
discrepancy between them and what you claim, is upsetting, all i can
say is whatever you want to insist won't change the box of
transformers I'm staring at. I suppose we could call the entire wall
wart industry a massive fraud for being overrated but I doubt it's
that simple.
You used the term "derating", are you saying it is not a derating
figure but rather a conversion figure?
** The figure was fully explained.
It derates the AC current figure to give the available DC current while not
exceeding the VA rating.
Thank you for clarifying, but I'm still in disbelief. Take this
example-
I have two typical looking E-core transformers rated for 32VA.
One of which was in a cordless drill quickcharger, it charged a pack
in an hour and also has an appropriate spec on it to accomplish that
per the battery pack cell capacity, 1.8A @ 12V Output (after going
through the control circuit).
This charger was used frequently for over 10 years. No failure on it,
no discolorations or smell like you'd have from excessive heat, looks
new inside except for a little bit of sawdust from the environment it
was occasionally used in. 'Twas only scrapped because it became less
viable to rebuild the battery packs another time on a drill after many
years of wear.
Based on your suggestion, even the upper end of getting 0.7 * AC
capacity, 0.7 * 32VA = 22.4VA. Output from the entire charger after
charge control board losses was 12V * 1.8A = 21.6. I think we both
know an old charger board is not 21.6/22.4 = 96.4% efficient!
I ask because you have gone on
and on about derating for temp, when I am very specifically looking
for only a mathematical equation for maximum transformer capability, a
theoretical one in a model that ignores temperature because the answer
is not going to be directly used to build something!
** You Q is just plain absurd.
Not in the context of using it as a starting point for an equation
upon which other variables are plugged in per the transformer and
application.
Transformer current and VA ratings are ALL about temp rise !!!!!!
ALL? Phil you seem to be stuck in infinite loop mode or something.
Regardless of whether you feel that way, I am talking about like
specs, there had to be a constant involved in the inital AC spec so
that remains the constant in the DC spec with regards to temperature.
What DC voltage and current is there, resolved mathematically, if we
allow the transformer to rise to the temp it would attain operating at
the AC voltage and current but not hotter than that? Wouldn't you
concede that in this case, a fair comparison would be if they are the
same temp so it isn't about temp rise at all? Some of the example
wall warts I have would tend to run quite a bit hotter than their free
air rating once placed in a sealed (or barely, passively ventilated)
plastic shell, and yet they don't have the thermal issues you imply
they should.
The regulation curve ( whether AC or DC plus rectifier /filter ) is a
function of VA and a number of other parameters plus the type of
construction used.
Agreed. Since the transformer itself is a constant, including it's
parameters and construction, I am looking for the remaining equation
of the AC voltage & current to DC voltage and current. I am looking
for the basic equation in which things that don't have to be
different, that can be held as constants like temperature and the
transformer being the same, are held as constants.
So are you claiming that if I short circuited the rectified output of
a transformer
** Never do that and I have never mentioned any such idiocy.
You are hee hawing like some barnyard ass now - pal.
Phil, I have a box of transformers and it's not a big deal to short
one of the smaller ones. Yes it'll smoke, maybe blow an internal fuse
or something but until it gets up to the high temps you fear it might
just last long enough to get a current reading. I was hoping to avoid
doing such things when I came here asking for an equation, but it
looks like testing is the only way to resolve this. Dead shorts
aren't necessary of course, but plotting data on several transformers
would seem useful if you were the only source of info on this topic.
If the shorted output power is not 20VA
** The power delivered into a short is always zero - fuckhead.
Are you saying it won't create heat, at least until something blows?
It sure seems like all that energy is going somewhere, and that it's
measurable.
But massive heat build up in the transformer will destroy it - pronto.
I'm sure it won't run long like that, but nevertheless you got the
jist of what I meant so who is being stubborn now?
because I am not asking about
implementation details for any transformer, only how to convert
mathematically to actual peak, not prudent design values.
** Utterly stupid question, only asked by fools.
If you had emailed me ahead of time before I ever started the thread
then I would have known what you wanted me to ask.
Unfortunately you failed to do so.
If it's complex math so be it.
** You do not need any complex math to size a tranny to do a given job.
Ah, but I do if I don't want to be half ignorant about it, if I have a
need to use one only large enough for the job, or if I need to know
whether one I had available is suitable, at least long enough to get a
prototype running or whatever the purpose.
There are lots of devices out there in the world that don't appear to
just size a transformer by throwing in one that's definitely larger
than it needs to be to supply the current and (your biggest concern)
stay cool enough not to fail or cause thermal stress to anything in
the vicinity), to have an acceptibly long service life without any
issues, unless the load itself causes excessive current and it blows
the thermal fuse.
Problem here is, you cannot even specify what the job is.
I especially do not want an equation that is only applicable to one
job. That would defeat the whole purpose.
Then the equation(s) used in that would be much closer to what I was
after.
** I don't give a shit what garbage you are after - fuckhead.
What you NEED is a damn good kick up the arse.
Pot and Kettle, Phil?
With all due respect Phil, you have no idea of the project
requirements beyond what I had told you.
** So you are now making then up as you go along - right ?
I am declaring them irrelevant constants because I am looking for an
equation that is independent of any one project. That's why I have
mentioned VARIABLES quite a few times, that it is not a problem to
have them to plug in later per any specific project.
A 40VA transformer is not going to work, unless it's one rated slightly
below 12V which is an odd figure.
** Totally insane crap.
Not work as-in, not meet the other criteria, I'm sure it'll supply the
minimal current in the example and then some but you still aren't
seeing that I am not looking for a recommendation for one project, it
was only an example posed towards coming up with a generic equation.
Again I will state that I should not have mentioned any specifics
about any project because it has distracted you too much.
Ultimately for that particular project I will most likely use a SMPS
instead, but that project was only an example not the question asked
which is what the equation is to determine AC to DC spec conversion.
I do not need an answer based on the limited specs of the transformer
info I had given, I only need the equation as complete as it can be
for future uses.
** The detailed specs you need are NOT published by makers.
You HAVE to measure individually them after you BUY a transformer !!!
I think you are right, to resolve some variables that will be
necessary. Even then, these seem to be less relevant variables as
there is a typical ratio of size to current rating that is above what
your 0.5 to 0.7 derating suggesting would dictate.
Just as quick to run a couple of bench tests if you have the damn tranny
right there in front of you.
Yes, I could run a test on every transformer but at some point one has
to pick the transformer to test, make a primary selection of
candidates and based on what I've seen there has to be a more accurate
way. Consider the example I posed above about a drill battery
recharger (which is not the same example as the other battery charger
project I initially posed), where the 32VA transformer is producing
enough power that if you were right, it should be too hot but it
isn't.
But I do not answer ridiculous Qs as specified by arrogant, bullshitting
novices
I'm starting to wonder if you've built nearly as many power supplies
as I have Phil. I have done similar to what you suggest in the past,
using vague ranges to derate as rules of thumb but I know there has to
be a better way and I observe far too many real world products that
contradict your claims, even if they are not so different than my
prior beliefs, and that they contradict my prior beliefs as well as
yours is part of what brought me here in the newsgroup to ask in the
first place.
No-one on usenet EVER has to do that.
I hope I've made things clearer.
** What you have made very clear is that you are an utterly autistic, rabid
nut case.
Are you sure it's transformers that are overheating?
Have a nice day Phil. It's not worth getting upset over.