audio recording on IC -help wanted

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Hi,

Sean Mathias wrote:

Thanks to all for the replies. To clarify some points as requested:

I am familiar with Ohm's law. I did, in fact, short the secondaries
through my DMM with current scale set to 10A, apparently a no-no, got
it.

It is not possible to do a google search as there are no markings
whatsoever on most of these transformers. Most of them were picked up
as surplus or parts from various places.

What I am trying to figure out is how to even approximate what the
'safe' or rated current is. Finding the secondary no-load voltages is
pretty straightforward, as is resistance, and determining the
different windings.

As for gradually adding load, I have done this, but what still eludes
me is that as resistance (load in this case) increases, current
increases and voltage drops. At what point do I know that the load is
at 'maximum' or design as I can continue to load it with a
corresponding decrease in voltage and increase in current.

Thanks for any help.

Sean

Tell us the dimensions of the iron core and the weight of your
transformer(s).

Martin.


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[Fred Bloggs]

Spehro Pefhany wrote:

On Sun, 10 Aug 2003 06:19:48 -0700, the renowned Watson A.Name - 'Watt
Sun' <alondra101@hotmail.com> wrote:


One Q. I've seen the LMC555 (or other CMOS 555) working off a 1.5V
cell. How far below 1.5V does it work?


TI has some that are (loosely) spec'd at 1.0V.

http://www.scanti.ru/docs/datasheets/slfs044b.pdf


Best regards,
Spehro Pefhany

There are also those wall-clock chips produced by the gazzillions-
overkill for a LED flasher but will do the job nicely- and low voltage too.

 

[indago]

030810 1609 - John Jardine wrote:

Sean Mathias <seanm@prosolve.com> wrote in message
news:nu0djvoksb09csgvpk5so5ulm0vimfh0sr@4ax.com...
Thanks to all for the replies. To clarify some points as requested:
[clip]

For small transformers.
1) Measure the largest open circuit voltage.
2) Add resistors across this output voltage until it drops by about 10%.
3) Measure the current flowing. This is the maximum current you should be
taking.
(less resistance means more current to the load)

Under full loading a transformer should get warm to hotish but not too hot
to touch.
regards
john

Or, you could give it the smoke test. Just keep adding load until it starts
to smoke, then reduce the load a little.

 

[C What I Mean]

BINGO! Finally someone has the easiest way. This is how we did it in the
surplus business years ago.

"John Jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:bh68el$jkr$1@newsg1.svr.pol.co.uk...

Sean Mathias <seanm@prosolve.com> wrote in message
news:nu0djvoksb09csgvpk5so5ulm0vimfh0sr@4ax.com...
Thanks to all for the replies. To clarify some points as requested:
[clip]

For small transformers.
1) Measure the largest open circuit voltage.
2) Add resistors across this output voltage until it drops by about 10%.
3) Measure the current flowing. This is the maximum current you should be
taking.
(less resistance means more current to the load)

Under full loading a transformer should get warm to hotish but not too hot
to touch.
regards
john

 

[Tweetldee]

"Sean Mathias" <seanm@prosolve.com> wrote in message
news:nu0djvoksb09csgvpk5so5ulm0vimfh0sr@4ax.com...

Thanks to all for the replies. To clarify some points as requested:

I am familiar with Ohm's law. I did, in fact, short the secondaries
through my DMM with current scale set to 10A, apparently a no-no, got
it.

It is not possible to do a google search as there are no markings
whatsoever on most of these transformers. Most of them were picked up
as surplus or parts from various places.

What I am trying to figure out is how to even approximate what the
'safe' or rated current is. Finding the secondary no-load voltages is
pretty straightforward, as is resistance, and determining the
different windings.

As for gradually adding load, I have done this, but what still eludes
me is that as resistance (load in this case) increases, current
increases and voltage drops. At what point do I know that the load is
at 'maximum' or design as I can continue to load it with a
corresponding decrease in voltage and increase in current.

Thanks for any help.

Sean

Well, your current measurement may not have been wasted after all. Take a
look at the procedure at http://home.earthlink.net/~jimlux/hv/xfmrmeas.htm
and give it a try. See what you come up with by using it on a transformer
for which you know all the specs. Ferinstance, a RadioShack unit with
ratings printed on the case. Then try it with some of your unknowns.

Before I found that site, I was thinking in terms of getting a physical
measurement of the wire in each of the windings. Convert the diameter of
the wires into circular mils, and use the typical design standard of 700
circular mils/amp to get a pretty close current rating for the secondaries.
How to do that.... you'll have to get to a small piece of the wire from
each secondary; a piece that's free of any coatings such as enamel,
insulating varnish, extraneous debris, etc. You may have to tear a small
patch of the outer layer of insulation away to get to the wire, but
generally, a small piece of wire is visible where it attaches to the
terminals. Of course, you'll have to go digging if the transformer doesn't
have solder terminals.
Using a caliper or micrometer, measure the diameter of the wire. Search the
web for an AWG table (very easy to find) that lists the diameter and
cross-sectional area (in circular mils), and find the circular mils for the
wire diameter just measured. Divide that number by 700 to get the
approximate current, in amps, that the secondary was designed for.

Double check it by the procedure laid out by the web site above. See how
close they come to each other.

I would be interested in hearing back from you as to which method comes
closest to the ratings of your known transformer.

Cheers!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.

 

[Dave VanHorn]

Before I found that site, I was thinking in terms of getting a physical
measurement of the wire in each of the windings. Convert the diameter of
the wires into circular mils, and use the typical design standard of 700
circular mils/amp to get a pretty close current rating for the
secondaries.
How to do that....

Depends also heavily, on the iron in the core.
How much, what type, how thick the lams are.

 

[Chris]

Or, you could give it the smoke test. Just keep adding load until it starts
to smoke, then reduce the load a little.

Yeah but once you've turned it into an SED how to you get the smoke
back in? ;-)

 

[no spam]

Chris wrote:

Or, you could give it the smoke test. Just keep adding load until it starts
to smoke, then reduce the load a little.



Yeah but once you've turned it into an SED how to you get the smoke
back in? ;-)


BMFH????

 

[Ghost Chip]

"Sean Mathias" <seanm@prosolve.com> wrote in message
news:2vbbjvshbchtj11ahqq4fl0i92ceoe2k6s@4ax.com...

My apologies for having to ask the same question again, but despote
the several helpful responses, I am still stumped.

I have many different power transformers and am trying to determine
their current ratings so I can select an appropriate one for a
project.

As I have not been able to get consistent results using various
methods, I decided to try measuring a power transformer that I do have
the specifications for. It is a Radio Shack (part number 273-1366A)
center tapped transformer 12.6-0-12.6V 0.45A.

What I don't understand is when I apply ~120VAC to the primary, the
secondary voltage reads approximately 14.0V, 4.5A between secondary
and center and 28.15V, 3.2A between secondaries.

So, with this transformer being rated at 0.45A, how and why am I
seeing >4A on a multimeter?

Again, the whole point of my exercise is to find a method of
determining the approximate current rating of different power
transformers (generally small transformers, so approximating by weight
is not too practical).

Thanks again,

Sean Mathias

Transformer design is a tradeoff between many things. For example, the
secondary current rating determines the wire size, sort of. Larger wire
means less voltage loss (I*R) in the winding and less heating (I*I*R).
Larger wire is more expensive and requires a larger transformer for the same
ratings but has less loss and less heating.
More current requires a larger core size in order to not saturate.
Saturation is when the steel core can't be magnetized any stronger therefore
no more energy can be "transformed" to the secondary. When this happens,
the primary current jumps to large values and can overheat the transformer
or worse!

A good rule of thumb and often a design spec for transformers, is the rule
already stated by John: "The rated current causes a 10% voltage drop from
open circuit voltage." So Johns trick is a good one to use for unknown
transformers. You'll always be close.
Zoramy

 

[Watson A.Name - 'Watt Sun]

In article <3F36B926.8010100@nospam.com>, nospam@nospam.com
mentioned...

Spehro Pefhany wrote:
On Sun, 10 Aug 2003 06:19:48 -0700, the renowned Watson A.Name - 'Watt
Sun' <alondra101@hotmail.com> wrote:


One Q. I've seen the LMC555 (or other CMOS 555) working off a 1.5V
cell. How far below 1.5V does it work?


TI has some that are (loosely) spec'd at 1.0V.

http://www.scanti.ru/docs/datasheets/slfs044b.pdf

Thanks for the info. So the CMOS 555 can serve as an alternative if
you don't mind the extra parts. But then, everyone knows the 555
astable circuit.

Best regards,
Spehro Pefhany

There are also those wall-clock chips produced by the gazzillions-
overkill for a LED flasher but will do the job nicely- and low voltage too.

But don't they need a xtal? Not something that you can come by
easily.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
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Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
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[Frank Bemelman]

"Tim Shoppa" <shoppa@trailing-edge.com> schreef in bericht
news:bec993c8.0308111313.3085fbf@posting.google.com...

I'm looking to buy a small quantity of kapton (or polyimide) tape.
It's going to be in an oven at near 100 degrees C and needs to be
dimensionally stable (an OCXO).

But... I only need a few square inches, and the distributors that I've
found via Google searches won't sell in quantities that small and I cannot
afford a whole roll (wow, it's expensive stuff). Any suggestions as to
where small quantities might be available?

Ask them for a free design sample.

--
Thanks,
Frank Bemelman
(remove 'x' & .invalid when sending email)

 

[R. Steve Walz]

Sean Mathias wrote:

My apologies for having to ask the same question again, but despote
the several helpful responses, I am still stumped.

I have many different power transformers and am trying to determine
their current ratings so I can select an appropriate one for a
project.

As I have not been able to get consistent results using various
methods, I decided to try measuring a power transformer that I do have
the specifications for. It is a Radio Shack (part number 273-1366A)
center tapped transformer 12.6-0-12.6V 0.45A.

What I don't understand is when I apply ~120VAC to the primary, the
secondary voltage reads approximately 14.0V, 4.5A between secondary
and center and 28.15V, 3.2A between secondaries.

So, with this transformer being rated at 0.45A, how and why am I
seeing >4A on a multimeter?

Again, the whole point of my exercise is to find a method of
determining the approximate current rating of different power
transformers (generally small transformers, so approximating by weight
is not too practical).

Thanks again,

Sean Mathias
-------------

Oh no, another idiot who thinks he can measure current capacity by
shorting the thing through a meter!! The danger of using a meter
without an education...
-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[Mjolinor]

-------------
Oh no, another idiot who thinks he can measure current capacity by
shorting the thing through a meter!! The danger of using a meter
without an education...
-Steve

Bit unfair, uneducated maybe but there is no evidence for the guy being an
idiot. If it concerns you that he doesn't know then educate him so that he
will know.

 

[Tony Williams]

In article <XW_Za.11908$Ye.10800@fed1read02>,
Ghost Chip <zoram@cox.net> wrote:

For a transformer that is 80% efficient, use a 4% rule for the
primary, and then 5% for the sec. Surprising how close it comes
out!

The example given was a bit artificial because I normally wouldn't
bother with R-sec and only do the estimate of the transformer's
total VA off an R-pri and 4% calc. It is usually a single sec (or
centre tapped) these days, so the VA and the unloaded Vsec voltage
is enough to get a reasonable guesstimate of the full load
secondary current.

--
Tony Williams.

 

[George R. Gonzalez]

"Barry Lennox" <pbarryplennoxp@operamail.com> wrote in message
news:tgjhjvgd54gemhfrrttfblejjkceu2du7c@4ax.com...

On 11 Aug 2003 14:13:23 -0700, shoppa@trailing-edge.com (Tim Shoppa)
wrote:

I'm looking to buy a small quantity of kapton (or polyimide) tape.
It's going to be in an oven at near 100 degrees C and needs to be
dimensionally stable (an OCXO).

You could try asking in one of the aviation technology newsgroups.
Kapton is used as insulation in many many commercial planes,
maybe some technician out there has some scraps he could part with.

 

[Howard Henry Schlunder]

"Fred Abse" wrote in message
newsan.2003.08.10.12.51.41.325153.658@cerebrumconfus.it...

On Sun, 10 Aug 2003 04:31:11 +0100, Sean Mathias wrote:

What I don't understand is when I apply ~120VAC to the primary, the
secondary voltage reads approximately 14.0V, 4.5A between secondary and
center and 28.15V, 3.2A between secondaries.

You're not just connecting an ammeter across each secondary and applying
power, are you?

If you are, don't, either you'll blow a fuse or the transformer will
saturate and get very hot.

Unlike inductors, transfomer core saturation is unrelated to current.
Transformer cores saturate from applying too much voltage per turn for too
long a period for the particular core material.




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[Tim Shoppa]

Watson A.Name - 'Watt Sun' <alondra101@hotmail.com> wrote in message news:<MPG.19a12c501a3936c1989bac@news.inreach.net>...

In article <3F36B926.8010100@nospam.com>, nospam@nospam.com
mentioned...


Spehro Pefhany wrote:
On Sun, 10 Aug 2003 06:19:48 -0700, the renowned Watson A.Name - 'Watt
Sun' <alondra101@hotmail.com> wrote:


One Q. I've seen the LMC555 (or other CMOS 555) working off a 1.5V
cell. How far below 1.5V does it work?


TI has some that are (loosely) spec'd at 1.0V.

http://www.scanti.ru/docs/datasheets/slfs044b.pdf

Thanks for the info. So the CMOS 555 can serve as an alternative if
you don't mind the extra parts.

Sort-of. The neat thing about the LM3909 is that when you run it off of
1.5V it delivers two-volt pulses to the LED. And when the battery is down
to 1.0V it's delivering about 1.5V to the LED, enough to be visible.

While on a fresh 1.5 cell a LMC555 will be blinking the LED, by the time
the cell voltage is down to 1.0V you won't be able to see the LED blink.
(Using a low-voltage incadescent bulb may do the trick, though.)

Tim.

 

[Harry Conover]

"Howard Henry Schlunder" <howard_hs@yahoo.com> wrote in message news:<3f390ed8$1_5@corp.newsgroups.com>...

"Fred Abse" wrote in message
newsan.2003.08.10.12.51.41.325153.658@cerebrumconfus.it...
On Sun, 10 Aug 2003 04:31:11 +0100, Sean Mathias wrote:

What I don't understand is when I apply ~120VAC to the primary, the
secondary voltage reads approximately 14.0V, 4.5A between secondary and
center and 28.15V, 3.2A between secondaries.

You're not just connecting an ammeter across each secondary and applying
power, are you?

If you are, don't, either you'll blow a fuse or the transformer will
saturate and get very hot.

Unlike inductors, transfomer core saturation is unrelated to current.
Transformer cores saturate from applying too much voltage per turn for too
long a period for the particular core material.

While what you say is quite true for pulse transformers, where
Volt-Second capacity and core saturation are directly related, it's
for me a bit of a stretch to apply the same concept to an a.c. power
transformer where entirely different issues are at play.

In designing a power transformer, core characteristic are more often
determined by an analysis of the combined magneto-motive force of all
its windings vis-a-vis the BH curves of the core material.

Harry C.

 

[Bill Bowden]

hhc314@yahoo.com (Harry Conover) wrote in message news:<7ce4e226.0308121352.1cf8aedc@posting.google.com>...

"Howard Henry Schlunder" <howard_hs@yahoo.com> wrote in message news:<3f390ed8$1_5@corp.newsgroups.com>...
"Fred Abse" wrote in message
newsan.2003.08.10.12.51.41.325153.658@cerebrumconfus.it...
On Sun, 10 Aug 2003 04:31:11 +0100, Sean Mathias wrote:

What I don't understand is when I apply ~120VAC to the primary, the
secondary voltage reads approximately 14.0V, 4.5A between secondary and
center and 28.15V, 3.2A between secondaries.

You're not just connecting an ammeter across each secondary and applying
power, are you?

If you are, don't, either you'll blow a fuse or the transformer will
saturate and get very hot.

Unlike inductors, transfomer core saturation is unrelated to current.
Transformer cores saturate from applying too much voltage per turn for too
long a period for the particular core material.

While what you say is quite true for pulse transformers, where
Volt-Second capacity and core saturation are directly related, it's
for me a bit of a stretch to apply the same concept to an a.c. power
transformer where entirely different issues are at play.

In designing a power transformer, core characteristic are more often
determined by an analysis of the combined magneto-motive force of all
its windings vis-a-vis the BH curves of the core material.

Harry C.

So, why does a microwave oven power transformer go into
saturation with no load? I tried one awhile back and it
drew over 3 amps from the line with no load. I assume it
was running into saturation since it was getting hot.

-Bill

 

[Eric Williams]

I have a 1986 National Programmable Logic Design Guide, what do you need?

"Colin Jackson" <jacksoncolin@yahoo.com> wrote in message news:<oYecnVNeLPAO3aSiXTWJiA@comcast.com>...

Anyone have a datasheet for a National PAL20L10?
(or any in the same family?)

Thanks,
Colin Jackson