audio recording on IC -help wanted

[Jim Adney]

On Mon, 04 Aug 2003 03:51:29 GMT "R. Steve Walz" <rstevew@armory.com>
wrote:

Jim Adney wrote:

Try a silicone PN diode

Silicon is the element used in solid state devices, silicone is the
plastic made with silicon as an atom in its matrix

You're right, of course. I was tired and my fingers were going faster
than my brain. This typo was the result.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

 

[Dave]

Dave Platt <dplatt@radagast.org> wrote in message
news:vj0hf3bug92ida@corp.supernews.com...

In article <bgpckd$m0e@library1.airnews.net>,
Dave <dbeane@genie.idt.net> wrote:

Not too slow for what I have in mind. I want to put it into a shortwave
radio, so that it holds its programming without power.

Unngh.

I think you'll find that the size of the necessary support electronics
(the pulse shapers/generators, line drivers, sense amps, etc.) is
likely to be prohibitive for that application.

If you actually want a solution which works (rather than a fun,
instructive, and maddeningly frustrating project to fiddle around
with) I'd suggest using a modern solution... a serial EEPROM, or a $2
PIC micro with onboard flash memory for code and EEPROM for data
storage, or an SRAM with a battery or supercap backup. Any of these
is going to be far less likely to visit upon you a severe case of
cerebral spasms.

Yeah, I'm slowly building this thing in my mind, and trying to decide just
how to approach this. It doesn't look simple in the least.

Dave
db5151@hotmail.com

 

[Thomas C. Sefranek]

"Marco_VE" <mdedin@email.it> wrote in message
news:vzRXa.2874$Y5.683@nntpserver.swip.net...

I need some info & pinout, or even better a datasheet, about IC 10131DC,
probably a Philips ECL family.
TNX a lot!!!

MC10131 Dual "D" Master Slave Flip-flop

--
*
| __O Thomas C. Sefranek WA1RHP@ARRL.net
|_-\<,_ Amateur Radio Operator: WA1RHP
(*)/ (*) Bicycle mobile on 145.41, 448.625 MHz

http://hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

 

[Louie]

Goran Larsson wrote:

Does it look like this < http://www.elfa.se/images/highres/h5312.jpg
but with the yellow stripe on it?

It could be a ferrite bead used for high frequency filtering or to stop
self oscillations. The color band could indicate the type of ferrite
material, i.e. what kind of frequency characteristics the bead has.

Bingo! looks like you got it. it looks almost exactly like that except
for the yellow stripe. and four of them are connected right off of the
secondary outputs of the transformer. two of the secondary outputs are
both connected to what looks like the ground trace, and the other four
have the mystery components comming off them.

and there is a 20kHz wave going through the transformer, your
description matches to a tee.

i'm gonna check the net for them just to make sure.

muchas gracias dude!
louie

 

[crooksie]

"Ivar Eriksen" <slegge@wildchat.REMOVE.org> wrote in message
news:bgsjb2$2did$1@news.dataguard.no...

Is it possible to place two LM317 in parallel in order to increase
wattage?
I got a bunch of LM 317T's wich is rated at 1.5 amps, and i need about 5
amps for an fan control circuit.

(I know an PWM circuit would be more efficent but i need to read the
strobe
pulse)


--
Slegge
WildChat.org

take a look at the application note
http://www.national.com/ds.cgi/LM/LM117.pdf
regards bob

 

[Costas Vlachos]

"Ivar Eriksen" <slegge@wildchat.REMOVE.org> wrote in message
news:bgsjb2$2did$1@news.dataguard.no...

Is it possible to place two LM317 in parallel in order to increase
wattage?
I got a bunch of LM 317T's wich is rated at 1.5 amps, and i need about 5
amps for an fan control circuit.

(I know an PWM circuit would be more efficent but i need to read the
strobe
pulse)

It is possible to parallel LM317s, but you can't simply connect their pins
together. A few more componenets are needed. Have a look at:

http://www.national.com/ds/LM/LM117.pdf

There is a typical app that shows how to do it. You could also use a pass
element to increase the output current. Check the typical apps in the above
data sheet.

Regards,
Costas
_________________________________________________
Costas Vlachos Email: c-X-vlachos@hot-X-mail.com
SPAM-TRAPPED: Please remove "-X-" before replying

 

[Dave]

Okay, okay. After due consideration and much thought, I am probably not
going to attempt this modification of my radio. Instead, I think I'll tape
an envelope to its back and place a list of stations/frequencies/times in
that. Same effect, much less effort overall. And more reliable. None of
this business of buying old core memory boards and taking them apart in
order to put something else together. I still might check it out just to
see what it would take, but for the FUN of it, that's all.

Thanks all.

Dave
db5151@hotmail.com

Dave Platt <dplatt@radagast.org> wrote in message
news:vj0hf3bug92ida@corp.supernews.com...

In article <bgpckd$m0e@library1.airnews.net>,
Dave <dbeane@genie.idt.net> wrote:

Not too slow for what I have in mind. I want to put it into a shortwave
radio, so that it holds its programming without power.

Unngh.

I think you'll find that the size of the necessary support electronics
(the pulse shapers/generators, line drivers, sense amps, etc.) is
likely to be prohibitive for that application.

If you actually want a solution which works (rather than a fun,
instructive, and maddeningly frustrating project to fiddle around
with) I'd suggest using a modern solution... a serial EEPROM, or a $2
PIC micro with onboard flash memory for code and EEPROM for data
storage, or an SRAM with a battery or supercap backup. Any of these
is going to be far less likely to visit upon you a severe case of
cerebral spasms.


--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Danny Stone]

Check Ebay - Old Core Modules show up all the time - a big expensive
though, since they're collectable.

There are better, more modern alternatives for what you want to do -
eeprom, flash, etc. come to mind...

Dave wrote:

Recently found out what "core" memory was and how it worked. Now I am
wanting to try an experiment to see if I can make use of some. Any idea as
to where one would look for old or "surplus" core memory, and maybe its
specs?

Thanks for any replies.

Dave
db5151@hotmail.com

 

[A E]

Christopher Bogart wrote:

I hope somebody here can help me in the right direction.

I bought a casino slot machine sign from ebay and it has 2 parts to it. A
top light sign and an LED display.

The led display is a dot matrix 8x8. They are stacked to form a row of 8.
You can see a pic of it here:

http://f2.pg.briefcase.yahoo.com/bc/cmjb13/vwp?.dir=/Electronics&.dnm=(8)+8x8+LED+front.jpg&.src=bc&.view=l&.done=http%3a//f2.pg.briefcase.yahoo.com/bc/cmjb13/lst%3f%26.dir=/Electronics%26.src=bc%26.view=l

This was tested with a 3 amp power supply and the display scrolls "No Data"
(obviously gets the data from the PCB inside the slot machine). I do not
have access to any schematics as you have to have connections or work in the
casino industry to get them. Even if that was available, parts for this
would only be sold to authorized casino individuals. So basically, I'm in
the dark.

Question 1: How to I get this LED to display text that I choose? (parts
needed, how to connect to PC, program to use, etc...)

The second part of the sign can be seen here:

http://f2.pg.photos.yahoo.com/bc/cmjb13/vwp?.dir=/Electronics&.dnm=Back+of+sign.jpg&.src=ph&.done=http%3a//f2.pg.photos.yahoo.com/bc/cmjb13/vwp%3f.dir=/Electronics%26.dnm=8x8%2b%2bLED%2bback.jpg%26.src=ph

There are LED's behind this sign as well, and my goal is to get it to
solidly light up (as opposed to flashing which the PCB controls).

I've had someone look at it and he doesn't know where the power comes from.
He believes it gets it's power from another source that is connected to this
piece. We tested it with the power supply and, while it made a very slight
noise, it did not light up at all.

Question 2: How can I get this to light up?

Any help is VERY appreciated.

Many thanks in advance

Chris

This looks like a CDS display. There is a jumper J2 labelled DATA IN. From what I remember, you need to constantly clock in new rows of display information. These displays are daisy chainable as well, you'll
see a connector labelled data out which plugs to the next display's data in. You also need to select which row to light up (it is multiplexed). You'll see 8 TO-220 transistors on the PCB, these supply the rows
with power. It's possible you have the three color version which means you have 128 LEDs per row to control.
You'd need a program that takes what you want to display, breaks it down into the correct bit patterns needed and sends out this information. Get a scope and look at how the NO DATA is sent to the display.

 

[A E]

Christopher Bogart wrote:

This is the 3 color version.

Looked like it, yeah.

There are black and red wires that go from the PCB to the LED board. The
other end of the wires were tested with the amp with the resulting "No Data"
color scheme.

Any ideas on what program I could use or how I would connect this?

Really, I don't, I believe CDS went belly up and because this is casino stuff, there's no info available. (it's more secret than nuclear weapons it seems)
I'm not aware of any program to drive this directly.
I'd take a scope, look at the signals on the data in connector, and work from that.
For sure, you have to clock in 128 bits at least for each row. I believe the chips driving the LEDs are the UCN5832s. You should have four of those on the board.
The hardest part will be breaking down your desired display into the bit patterns needed.
But, you seem to have the main board of the system that can display the 'NO DATA' string, so there must be a system in there already... I don't know anything about that, sorry.

 

[Joshua K Drumeller]

Just measure the voltage not the amperage. you are only supposed to measure
amperage (current) when you have a load attached. Just attaching the
multimeter across the transformer to measure current is the wrong way and
you will get useless results.You put the ammeter in series between the
transformer and the load. The load you attach will draw only the current
required for it to run. it will not draw the 4 or the 3.2 amps you measured.
The current ratings on a transformer are only there to say "be sure the load
you attach don't use more current than this".

Ideally the center tap should be exactly half the voltage as the two ends.
But, in the real world the voltage between one side and the centertap will
be slightly different than the other side to the centertap. But it is not
much to make any real difference.

If the transformer has any markings or numbers on it you can do a search on
yahoo or google with those to get its specifications on a data sheet. If it
doesn't have these, see if it has any power ratings written on it . It
might be something like 300W for 300 watts or maybe 100VA for 100
VoltAmps (different than watts). These specifications are saying that the
transformer can only supply up to this much to the load. From this
specification and a little math you can get the maximum current you can run
through there. Which you might not even have to do if the load you attach
uses only a little current.

If this is all new to you I recommend studying a little more before you
proceed with your transformer project.

Josh

"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

 

[Don Kelly]

"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?

----------

Are you looking at both a current and voltage scale on the meter? read one
or the other.
14V appears to be an open circuit voltage (0 current). If you are separately
measuring a short cicuit current of 4A (voltage=0) then the current reading
makes sense- otherwise not.
More details of what you actually measured would help.

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).
----------

Open and short circuit measurements will give you useful information about
the transformer but will not give you the current rating.

--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer

Thanks again,

Sean Mathias

 

[Tom Grqyson]

"Sean Mathias" <seanm@prosolve.com> wrote in message | So, with this


| 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).


Sean.
Further to the comments already posted by Josh and Don.

The power rating of most electrical devices is the maximum power
you can get from it on a continuous basis, without the thing failing. There
are margins on the figures quoted so that variations in ambient temperature
and perhaps altitude, can be accomodated. Usually the Safety codes of
individual countries also demand some margin as well.

Generally speaking, exactly what the limiting factor is, of any particular
device, depends on the device and how it is constructed.

It could be the quality of the insulating material, It could be the size of
the cable supplying it, or perhaps the rating of the input fuse ( if it has
one) or the size of the actual conductors inside it.

The point is that no simple test will give you the answer because the
limiting
factor could be anything.

You might try looking for a change in voltage with an increasing load and
find out how much current draw will drop the output voltage below your
tolerence band, however you do not know if this amount of power could
produce a hot spot somewhere, possibly leading to insulation catching fire.

Your best bet is to follow the advice given in the other posts such as
looking for printed watt or VA or VoltAmps ratings on the casing.

Perhaps there is a fuse on the input side, it will have a curent rating
printed on it. This may give you a pointer.
From What I have seen, These fuses must be included, and are genreally non
replaceable. You would probably have to pull apart the casing to find this
so it might be self defeating proceedure.

Put simply, You need to find data on the device. Look it up on the web, Look
in the radio shack catalog, or Look for printing on the outside.

Most sorts of simple tests will not give you the answer.

Tom Grayson

 

[Fred Abse]

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.

If you want to determine a transformer's current rating, the only way to
do it safely is apply a series of decreasing loads (resistors) to all the
secondaries simultaneously until the voltage falls to the nominal (in
this case 12.6V. V/R will then give you the current.

Open circuit, any transformer will show more voltage than loaded, due to
iron and copper losses. The trick is to design so that the voltage is
correct *on load*.

--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx

 

[Watson A.Name - 'Watt Sun]

In article <t46bjv8ta05scsoev2r6ajjfhignmekb7t@4ax.com>, Jim-
T@analog_innovations.com mentioned...

On 9 Aug 2003 17:52:19 -0700, rpaisley4@cogeco.ca (Rob Paisley) wrote:

Brooke Clarke <brooke@pacific.net> wrote in message news:<vj7ifcavm6m3f8@corp.supernews.com>...
Hi:

Since the LM3909 flasher chip is long out of production is there a
replacement chip or circuit that has the same or lower power consumption
(assuming the same LED was used on both)?
I did find a web page that implemented the schematic from the LM3909
using discrete components. Is this the lowest power consumption approach?

Thanks,

Brooke Clarke, N6GCE

You can reduce the curent draw of this circuit -
http://home.cogeco.ca/~rpaisley4/LM3909.html - by increasing the
values of the resistors in the circuit.

The circuit worked fine when R3 and R4 were doubled.

Rob.

Q2 should be diode driven (which is what that lateral PNP
representation is equivalent to). The website implementation may be
prone to leakage problems at high temperatures.

My attempt at ASCII:

---------------(5)
| |
\ | | /
|---+----|
| | |
/| | | \
|_____| |
| |
(B) (C)



...Jim Thompson

I think he ought to rename it Dis-integrated Circuit.

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?


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Watson A.Name - 'Watt Sun]

In article <2vbbjvshbchtj11ahqq4fl0i92ceoe2k6s@4ax.com>,
seanm@prosolve.com mentioned...

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?

Just exactly how are you measuring the current? Short circuit? Have
you considered that your methods are incorrect or your meter is
misleading you?

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

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Joshua K Drumeller]

Also don't forget the voltage and current your measuring with your
multimeter is RMS not peak.

Josh

"Joshua K Drumeller" <lkfightr@swbell.net> wrote in message
news:t7kZa.335$iS5.209@newssvr24.news.prodigy.com...

Just measure the voltage not the amperage. you are only supposed to
measure
amperage (current) when you have a load attached. Just attaching the
multimeter across the transformer to measure current is the wrong way and
you will get useless results.You put the ammeter in series between the
transformer and the load. The load you attach will draw only the current
required for it to run. it will not draw the 4 or the 3.2 amps you
measured.
The current ratings on a transformer are only there to say "be sure the
load
you attach don't use more current than this".

Ideally the center tap should be exactly half the voltage as the two ends.
But, in the real world the voltage between one side and the centertap will
be slightly different than the other side to the centertap. But it is not
much to make any real difference.

If the transformer has any markings or numbers on it you can do a search
on
yahoo or google with those to get its specifications on a data sheet. If
it
doesn't have these, see if it has any power ratings written on it . It
might be something like 300W for 300 watts or maybe 100VA for 100
VoltAmps (different than watts). These specifications are saying that the
transformer can only supply up to this much to the load. From this
specification and a little math you can get the maximum current you can
run
through there. Which you might not even have to do if the load you attach
uses only a little current.

If this is all new to you I recommend studying a little more before you
proceed with your transformer project.

Josh

"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

 

[Terry]

In article <2vbbjvshbchtj11ahqq4fl0i92ceoe2k6s@4ax.com>,
seanm@prosolve.com mentioned...

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?

If you actually had about 4 amps flowing through out of a
secondary that is only rated for 0.45 amps it's a wonder that you
didn't overheat the transformer and burn it, or something else,
out? Maybe you were just lucky! Overheating a transformer can
lead to burnt up windings, burn insulation which in turn can
cause contact between different windings! See Note 1.

To understand what you are doing maybe you should do some ohms
law calculations.
For example;
14.0 volts across a 140 ohm lamp is; 14/140 = 0.1 amps.
14.0 volts across a 70 ohm lamp or resistor is; 14/70 = 0.2 amps
14.0 volts across a 10 ohm resistor is; 14/10 = 1.4 amps
14.0 volts across an almost dead short circuit (or maybe the
internal resistance of an ammeter if that didn't burn up the
internal shunt resistor inside the meter!) could be 14.0 volts
across 3 ohms = 4.7 amps. Don't do that; transformers (or
ammeters either) don't like short circuits that's why good
circuits should have small fuses in the transformer primary.

Note 1: I had a transformer that worked OK and delivered the
rated voltage from its secondary; unfortunately it had been
overheated at some time and the heat had caused the secondary to
be in electrical contact with the primary. So the radio of which
the transformer was a part was electrically 'hot' and when one
touched the radio you got a shock from the AC mains input!

Note 2. I respectfully suggest, but this is only a supposition,
that the total ohmic resistance in the secondary winding of such
a transformer, the meter leads and the shunt resistor inside the
meter may have been 'just sufficient' to limit the current to 4.5
amps and if not connected for too long may have prevented severe
damage? 4.5 amps at 14 volts is approximately 63 watts! Imagine
the heat of a 60 watt bulb that turns most of it's electrical
input into heat going into the insides of a transformer; it is
not mentioned if anything got warm/hot?

I don't understand what the original poster means by 28.15 at 3.2
amps 'between' secondaries? If it was voltage due to capacitance
there wouldn't be any current flowing. But there is possibility
of seeing voltage between any two parts of the transformer due to
capacitance effect and depending on the AC impedance of his
meter.

Unless the poster does not know how to connect and read the
ammeter setting of the meter?

It's all very confusing about what he is doing and trying do?
From what I've understood it's very lucky that secondary windings
didn't burn out with ten times their design current and/or the
transformer/s didn't catch fire! Keep a fire extinguisher handy.

 

[Rusty]

On Sat, 09 Aug 2003 20:31:11 -0700, Sean Mathias
<seanm@prosolve.com> 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

If, as others have surmised, you short circuited your transformer
with your multimeter set to a high current setting - like 10 amps -
then you have taken an awful risk of burning out your meter. On the
other hand, if you read the current scale on an analog meter when
set to volts, then the reading is meaningless.

The rating of the Radio Shack transformer is the maximum current it
should be allowed to deliver for an extended period of time without
overheating and risking burning out. All ratings are ultimately
decided in this way. If you connect a load across the transformer
that just draws the rated current, the voltage should drop from the
open circuit voltage to 12.6 volts, due to internal resistance of
the windings.

There are many simple books available that describe exactly how a
transformer works. It might be worthwhile borrowing one from your
local library to understand the principles. Also read up on the use
of your multimeter. Depending on the setting of the range selector,
you can read either volts or amps or possibly resistance in ohms,
but only one at a time.

 

[Sean Mathias]

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

On Sun, 10 Aug 2003 16:41:55 GMT, rtotman@oanet.com (Rusty) wrote:

On Sat, 09 Aug 2003 20:31:11 -0700, Sean Mathias
seanm@prosolve.com> 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

If, as others have surmised, you short circuited your transformer
with your multimeter set to a high current setting - like 10 amps -
then you have taken an awful risk of burning out your meter. On the
other hand, if you read the current scale on an analog meter when
set to volts, then the reading is meaningless.

The rating of the Radio Shack transformer is the maximum current it
should be allowed to deliver for an extended period of time without
overheating and risking burning out. All ratings are ultimately
decided in this way. If you connect a load across the transformer
that just draws the rated current, the voltage should drop from the
open circuit voltage to 12.6 volts, due to internal resistance of
the windings.

There are many simple books available that describe exactly how a
transformer works. It might be worthwhile borrowing one from your
local library to understand the principles. Also read up on the use
of your multimeter. Depending on the setting of the range selector,
you can read either volts or amps or possibly resistance in ohms,
but only one at a time.