On Jul 11, 2:34 pm, ehsjr
e.h.s.j.r.removethespampunctuat... at (no spam) bellatlantic.net> wrote:

I don't want to argue - that seems your intent.
I know you want a magic formula - you have made that
clear.  There is no single formula for you.  Those who
have replied have made that clear.

We've tried to show you some of the factors that are
involved.  You insist on ignoring them.  So, we can't
help you, no matter how hard we try.  Sorry.

A formula yes, but no it's not magic. It simply requires considering
all the significant variables which I'd hoped others would assist
with, but obviously nobody else wants to do more than argue instead of
putting thought into what such an equation would look like. If you
say "it depends", then that should be in an equation. If you say some
other thing depends too, then that too can be put into the equation.

There is an equation that could be made. How accurate the answer from
it would depend on how complete it was.

I don't want to argue - that seems your intent.
I know you want a magic formula - you have made that
clear. There is no single formula for you. Those who
have replied have made that clear.

We've tried to show you some of the factors that are
involved. You insist on ignoring them. So, we can't
help you, no matter how hard we try. Sorry.

emailaddress at (no spam) insightbb.com


I am not designing a charging circuit.


** You are NOT designing ANYTHING AT ALL

YOU STINKING CRIMINAL LIAR !!!!!!!!!!


FOAD - you anonymous pile of shit.




..... Phil

On Sun, 13 Jul 2008 01:02:47 +1000, "Phil Allison"
philallison at (no spam) tpg.com.au> wrote:


emailaddress at (no spam) insightbb.com


I am not designing a charging circuit.


** You are NOT designing ANYTHING AT ALL

YOU STINKING CRIMINAL LIAR !!!!!!!!!!


FOAD - you anonymous pile of shit.




..... Phil





http://www.sfgate.com/cgi-bin/object/article?o=6&f=/c/a/2008/07/12/DDCOMICS12.DTL

John

On Jul 12, 7:40 am, emailaddr... at (no spam) insightbb.com wrote:
..snip..

However, it is fairly beside the point that I am looking for
a universal equation that ignores all of this. Many people seem to be
saying the rest matters and yes of course it does - but it is still
theoretically expressable in an equation with the factors that change
as variables.


Universal equation. Here you go.

http://en.wikipedia.org/wiki/Heat_equation
http://en.wikipedia.org/wiki/Newton%27s_law_of_cooling#Newton.27s_law_of_cooling

Also check out "Introduction to Heat Transfer" by Incropera and
DeWitt.

The game is to keep the transformer wires at only a moderate
temperature higher than ambient, or you will melt the wiring
insulation.

Knock yourself out.

Michael

On Sat, 12 Jul 2008 07:56:53 -0700 (PDT), emailaddress at (no spam) insightbb.com
wrote:


On Jul 11, 2:34 pm, ehsjr
e.h.s.j.r.removethespampunctuat... at (no spam) bellatlantic.net> wrote:


I don't want to argue - that seems your intent.
I know you want a magic formula - you have made that
clear. There is no single formula for you. Those who
have replied have made that clear.

We've tried to show you some of the factors that are
involved. You insist on ignoring them. So, we can't
help you, no matter how hard we try. Sorry.

A formula yes, but no it's not magic. It simply requires considering
all the significant variables which I'd hoped others would assist
with, but obviously nobody else wants to do more than argue instead of
putting thought into what such an equation would look like. If you
say "it depends", then that should be in an equation. If you say some
other thing depends too, then that too can be put into the equation.

There is an equation that could be made. How accurate the answer from
it would depend on how complete it was.


---
Funny, meteorologists feel the same way, and yet it seems that
detecting that last elusive flap of butterfly wings has been
perpetually beyond their grasp.

JF

On Jul 11, 4:07 pm, mrdarr... at (no spam) gmail.com wrote:

On Jul 9, 6:39 pm, emailaddr... at (no spam) insightbb.com wrote:






On Jul 9, 9:26 pm, emailaddr... at (no spam) insightbb.com wrote:

I have an application in which I need to determine if a transformer is
suitable.
Perhaps a little more info about the project is in order. Following
the transformer there'll be a bridge rectifier, smoothing cap... then
a linear regulator suppling constant current to charge batteries. The
circuit is a bit more involved than only this (protection diodes,
charge controller, etc) but this is the subsection in question and the
rectified output of the transformer will need to stay above roughly
12.3VDC so I'm trying to figure out what constant current this
transformer (or others) can supply.

Another thing I am wondering is if a basic, typical small brick AC-DC
switching supply is stable powering this kind of load. Stripping down
the circuit to the basic topology, what if it had for example:

AC-DC SMPS -> LM317 -> 1.25 Ohm resistor (LM317 in current regulating
config) -> 1A into Battery Pack + LM317 feedback

Since the SMPS is trying to regulate to it's spec'd voltage, let's say
that is 13V even if an uncommon value, will it run stable doing so and
if so, is that at the same constant output wattage from the SMPS the
whole time, with the linear regulator simply dropping more voltage,
creating more heat at the beginning of a battery recharge cycle since
it's suppling constant current to batteries that are at a lower
initial, low state-of-charge voltage?

Why so many LM317s? They will generate heat too, and waste energy.


First, the example is not something I intend to build at all, it is
just providing an example, a load.

Second, in the example there is only one LM317, when I mentioned
"LM317" the 2nd and third time I was only describing the typical
topology of using one LM317 in the context of it being in current
limiting mode. I used an example that is straight from National's
LM317 datasheet since many would presumably be familiar with it.


What are you charging? What supply voltage do you need?



I am not building that example. The first example or something fairly
similar I did build a few years ago but now I have no need to consider
the charging or other aspects of the circuit beyond the supply to it,
because it used to be a stationary charger with capability of charging
several different sized packs but it has been reused now for a single
set of packs all with 6 cells. Therefore the most desirable supply
has changed from what it used formerly to something more closely
matched. However, it is fairly beside the point that I am looking for
a universal equation that ignores all of this. Many people seem to be
saying the rest matters and yes of course it does - but it is still
theoretically expressable in an equation with the factors that change
as variables.

if it has any meaning at all for the subject..

John Fields wrote:
On Sat, 12 Jul 2008 07:56:53 -0700 (PDT), emailaddress at (no spam) insightbb.com
wrote:


On Jul 11, 2:34 pm, ehsjr
e.h.s.j.r.removethespampunctuat... at (no spam) bellatlantic.net> wrote:


I don't want to argue - that seems your intent.
I know you want a magic formula - you have made that
clear. There is no single formula for you. Those who
have replied have made that clear.

We've tried to show you some of the factors that are
involved. You insist on ignoring them. So, we can't
help you, no matter how hard we try. Sorry.

A formula yes, but no it's not magic. It simply requires considering
all the significant variables which I'd hoped others would assist
with, but obviously nobody else wants to do more than argue instead of
putting thought into what such an equation would look like. If you
say "it depends", then that should be in an equation. If you say some
other thing depends too, then that too can be put into the equation.

There is an equation that could be made. How accurate the answer from
it would depend on how complete it was.


---
Funny, meteorologists feel the same way, and yet it seems that
detecting that last elusive flap of butterfly wings has been
perpetually beyond their grasp.

JF

:-) Nice analogy, wonder if he'll get it.

What is interesting to me is the apparent contradiction in
the op's thinking. He chooses to lecture respondents with
his thinking, rather than attempt to understand what they
are saying. Or, if not lecture, argue with points that are
made. I've seen this a few times here - someone comes here,
states that they don't know about X, and asks a question.
But then they argue with the answer! What kind of thinking
is that? Is it the "new way of thinking" or ???

For example, lets assume you have 120 volt service into a wallwart, the
unit outputs 12 volts, this would be a 10:1 ratio. So if we were to
measure lets say 200 ohms on the primary side, we would thus scale that
down by 10 = 20 ohms. The DC resistance on the secondary side is simply
added to this to give you a sum R..

I've seen it a few times also, and I think it's a way of trying to
save face by not admitting that the gift that was given incurred
emotional indebtedness.

That is, if you give me a gift of knowledge and I dis it, I'll still
have the gift but in my mind I won't owe you anything for it.

Make sense?

"Jamie" = Maynard A. Philbrook = radio ham KA1LPA

WARNING: Ignore everything this total moron posts.



For example, lets assume you have 120 volt service into a wallwart,
the unit outputs 12 volts, this would be a 10:1 ratio. So if we were to
measure lets say 200 ohms on the primary side, we would thus scale that
down by 10 = 20 ohms. The DC resistance on the secondary side is simply
added to this to give you a sum R..


** WRONG !!!!!!!!

Primary resistance appears at the secondary divided by the SQUARE of the
transformer's actual turns ratio.

The turns ratio is always less than the nominal voltage ratio, to allow
for voltage drop under load, so - for the above case, ( very small
transformer) the turns ratio is about 8 and reflected resistance is
therefore 200 /64 = 3.13 ohms.

"John Fields"

I've seen it a few times also, and I think it's a way of trying to
save face by not admitting that the gift that was given incurred
emotional indebtedness.

That is, if you give me a gift of knowledge and I dis it, I'll still
have the gift but in my mind I won't owe you anything for it.

Make sense?


** If you imagine some little a brat throwing a toy that is not the one he
wanted back at Santa.

---

emailaddress at (no spam) insightbb.com


I am not designing a charging circuit.


** You are NOT designing ANYTHING AT ALL

YOU STINKING CRIMINAL LIAR !!!!!!!!!!


FOAD - you anonymous pile of shit.

Can't you just feel the love?

On Sun, 13 Jul 2008 01:02:47 +1000, "Phil Allison"
philallison at (no spam) tpg.com.au> wrote:


emailaddress at (no spam) insightbb.com


I am not designing a charging circuit.


** You are NOT designing ANYTHING AT ALL

YOU STINKING CRIMINAL LIAR !!!!!!!!!!


FOAD - you anonymous pile of shit.

Can't you just feel the love?

On Jul 11, 4:37 pm, John Fields <jfie... at (no spam) austininstruments.com> wrote:
On Wed, 9 Jul 2008 18:26:12 -0700 (PDT), emailaddr... at (no spam) insightbb.com
wrote:





I have an application in which I need to determine if a transformer is
suitable.

Transformer is rated for 12VAC, 1.67A but I need DC.  I could put a
bridge rectifier and capacitor after it easily enough but how does one
go about calculating the DC output this is capable of?

I've previously used a x 1.41 factor to convert which would give
16.92V, minus the forward drop of a couple silicon diodes in the
bridge rectifier estimated at roughly ( 2 * 0.7V, ignoring changes in
diode forward drop at different current) which would leave (16.92 -
1.4) = 15.5V, but am I correct in thinking this is peak DC output and
there is a different calculation needed to arrive at the output
voltage if the load were drawing 1.67A?

Perhaps a little more info about the project is in order.  Following
the transformer there'll be a bridge rectifier, smoothing cap... then
a linear regulator suppling constant current to charge batteries.  

Why can't you just used the raw unfiltered DC and current limit the
input to the battery?


I am not designing a charging circuit. The charging circuit is fixed,
done years ago, works fine. It's just being mated with a different
supply because the need for it has changed. I am looking for an
equation to qualify transformers per their AC spec for DC supply when
used with a basic bridge rectifier following them.