Chip with simple program for Toy

[Bob Masta]

On Wed, 13 Feb 2008 09:02:15 -0500, "jamesgangnc" <james@nospam.com>
wrote:

I want to build the killer of all dog bark stoppers. (Sorry to any dog =
lovers but we have neighbors with two dogs that they leave in a fenced =
yard and they bark at anything that happens within a 1/2 mile day or =
night.) I already have a device I bought that is tripped by barking and =
has a couple piezo tweeters in it. Not enough power though. I've got a =
power supply I salvaged out of some com gear that does 70 amps of +5 so =
I was thinking I could use some high current power transistors to run a =
whole bunch of those cheap piezo tweeters in parallel. I can adapt =
existing circuits and combine designs but designing from scratch is a =
little beyond my skills. Also I need parts suggestions for the power =
transistor. I know I need an amp design that has a lot of current gain, =
not voltage gain. And something I can run several of the amp circuits =
in parallel if I need to. I was planning to drive it from the output =
circuit of the existing bark stopper unit if I can. Otherwise if I need =
to I can interject some opamps (741s) or common low power transistors =
like the 2n2222 or 2n2907s to drive. I have a old tectronix 5mhz scope =
and digital multi-meter and a collection of basic parts. Figuring I'll =
have to get the power transistors from newark.=20

I'd previously been thinking about running a bunch of the piezoes in =
series and using the 115v mains directly into dc with some sort of high =
voltage amp circuit but then this 70 amp 5v power supply came along. =
Figured it's be a lot safer that rectified mains.

Anyone want to give me some pointers?

I suspect that you don't need anything in the way of waveform fidelity
for this application, so your amplifier doesn't need to be anything
more than a switching transistor. I imagine that is what the
commercial unit uses already, so you may be able to poke around inside
it and find a decent drive signal. It should be a rectangular wave
running between ground and the positive supply voltage.

Probably just about any TO-220 or similar NPN power transistor
will work. Connect the drive signal to the base through 1K or so,
ground the emitter, and connect the piezo unit between the collector
and the positive supply.

I am assuming here that the piezo units are not self-contained buzzers
that produce a fixed frequency when DC is applied. If so (and you buy
more just like them) then the same simple switching circuit will still
work, except that the drive signal will be a DC level that lasts as
long as the sound is supposed to last.

Note that piezo devices in general are low current, high voltage
devices, so depending on the exact model they may do better with more
than 5V. (But getting decent specs is difficult.) They also don't
put out a lot of power, but a whole lot of cheap piezos may still be
cheaper than a high-power dynamic super-tweeter.

Of course, all cheap piezo tweeters don't have the same frequency
reponse, either, so you may want to experiment with a few different
models.

Best regards.


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[jamesgangnc]

On Feb 14, 8:51 am, NoS...@daqarta.com (Bob Masta) wrote:

On Wed, 13 Feb 2008 09:02:15 -0500, "jamesgangnc" <ja...@nospam.com
wrote:





I want to build the killer of all dog bark stoppers.  (Sorry to any dog > >lovers but we have neighbors with two dogs that they leave in a fenced > >yard and they bark at anything that happens within a 1/2 mile day or > >night.)  I already have a device I bought that is tripped by barking and > >has a couple piezo tweeters in it.  Not enough power though.  I've got a > >power supply I salvaged out of some com gear that does 70 amps of +5 so > >I was thinking I could use some high current power transistors to run a > >whole bunch of those cheap piezo tweeters in parallel.  I can adapt > >existing circuits and combine designs but designing from scratch is a > >little beyond my skills.  Also I need parts suggestions for the power > >transistor.  I know I need an amp design that has a lot of current gain, > >not voltage gain.  And something I can run several of the amp circuits > >in parallel if I need to.  I was planning to drive it from the output > >circuit of the existing bark stopper unit if I can.  Otherwise if I need > >to I can interject some opamps (741s) or common low power transistors > >like the 2n2222 or 2n2907s to drive.  I have a old tectronix 5mhz scope > >and digital multi-meter and a collection of basic parts.  Figuring I'll > >have to get the power transistors from newark.=20

I'd previously been thinking about running a bunch of the piezoes in > >series and using the 115v mains directly into dc with some sort of high > >voltage amp circuit but then this 70 amp 5v power supply came along.  > >Figured it's be a lot safer that rectified mains.

Anyone want to give me some pointers?

I suspect that you don't need anything in the way of waveform fidelity
for this application, so your amplifier doesn't need to be anything
more than a switching transistor.  I imagine that is what the
commercial unit uses already, so you may be able to poke around inside
it and find a decent drive signal. It should be a rectangular wave
running between ground and the positive supply voltage.

Probably just about any TO-220 or similar NPN power transistor
will work.  Connect the drive signal to the base through 1K or so,
ground the emitter, and connect the piezo unit between the collector
and the positive supply.

I am assuming here that the piezo units are not self-contained buzzers
that produce a fixed frequency when DC is applied.  If so (and you buy
more just like them) then the same simple switching circuit will still
work, except that the drive signal will be a DC level that lasts as
long as the sound is supposed to last.

Note that piezo devices in general are low current, high voltage
devices, so depending on the exact model they may do better with more
than 5V.  (But getting decent specs is difficult.)  They also don't
put out a lot of power, but a whole lot of cheap piezos may still be
cheaper than a high-power dynamic super-tweeter.

Of course, all cheap piezo tweeters don't have the same frequency
reponse, either, so you may want to experiment with a few different
models.

Best regards.

Bob Masta

              DAQARTA  v3.50
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
        Science with your sound card!- Hide quoted text -

- Show quoted text -

Thanks for the advice. You are absolutely correct, sound quality is
not an issue. I doubt the unit I'm planning to drive it with has a
very clean sine wave. Would you put a capacitor in the circuit
between the source and the npn transistor as well? I don't need any
sort of bias? How many do you think I can hang off one TO-220? Yes
the tweeters are those cheap piezo ones, not buzzers. Something like
these;

http://www.fcsurplus.ca/shopping/shopexd.asp?id=16013

 

[JeffM]

jamesgangnc TOP-POSTED
(without any marking to show who posted what):
Your posting style SUCKS.
http://www.google.com/search?q=cache:bLfLqbwDHOQJ:www.mozilla.org/community/etiquette.html+in.logical.order+Us+after.the.text.you.are.commenting.upon+remove.extraneous.material+Top-posting

Ah.
http://groups.google.com/group/sci.electronics.basics/msg/b5a8ff210b586310?dmode=source
It might help if you would configure the PoS tool you use.

 

[Bob Masta]

On Thu, 14 Feb 2008 10:56:32 -0800 (PST), jamesgangnc
<jamesgangnc@earthlink.net> wrote:

Thanks for the advice. You are absolutely correct, sound quality is
not an issue. I doubt the unit I'm planning to drive it with has a
very clean sine wave. Would you put a capacitor in the circuit
between the source and the npn transistor as well? I don't need any
sort of bias? How many do you think I can hang off one TO-220? Yes
the tweeters are those cheap piezo ones, not buzzers. Something like
these;

http://www.fcsurplus.ca/shopping/shopexd.asp?id=3D16013

Couldn't get that link to work, so I can't comment on the specific
part.

No, you don't need (or want) any capacitor or bias on the driver
transistor... it's just acting as a simple switch. When the input
is at ground, it's off. When the input rises a few volts it goes
fully on. Note that this depends upon the signal being a clean
rectangular wave swinging between ground and positive supply...
not a regular bipolar AC signal and definitely not a sine wave.

As far as how many tweeters you can hang off one TO220, "that
depends"... but probably several. Try experimenting and seeing how
warm it gets. If the signal frequency is too high to hear, you may
want to test your circuit with a somewhat lower frequency so you can
be sure everything is working OK. Again, it must swing between ground
and the positive supply. You may be able to lower the drive frequency
by locating the capacitor in the oscillator stage and jumpering a
larger one across it. Or, if you can get the appropriate signal from
a benchtop signal generator, use that. If you have a proto-board and
a couple of CMOS gates, you can rig up a simple oscillator to do the
job. (Post back if you need a circuit, but I suspect there are plenty
on the Web. The "CMOS Cookbook " by Don Lancaster is an excellent
source for this kind of thing.)


Best regards,




Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

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[davidt]

On 25 Feb, 12:43, "amdx" <a...@knology.net> wrote:

"davidt" <da...@talktalk.net> wrote in message

news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...

I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

  You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will have
less turns if thicker wire. (it carries more current)

Yes that makes sense now when think about the current.
Thanks for your help.

 

[Jon Slaughter]

"amdx" <amdx@knology.net> wrote in message
news:5fe78$47c2b7ac$18d6b40c$13581@KNOLOGY.NET...

"davidt" <dav1d@talktalk.net> wrote in message
news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...
I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will have
less turns if thicker wire. (it carries more current)

Only smaller wire because the current requirements are smaller. There is no
restriction on the wire size for a transformer except that it be able to
handle the current. (so it definitely could have been larger)

 

[JeffM]

Dwight D. Eisenhower (Charles M. Nudo, Jr.) wrote:
http://groups.google.com/groups/search?q=author:Eisenhower+cgi.ebay&scoring=d&filter=0&num=100
http://groups.google.com/groups/search?q=Charles+OR+Charlie+Nudo+-nude&scoring=d&filter=0&num=100

....and, of course, Google Groups is in the loop.

 

[steve]

On Feb 14, 12:28 am, JeffM <jef...@email.com> wrote:

jamesgangnc wrote:
I want to build the killer of all dog bark stoppers.
[...]we have neighbors with two dogs that they leave in a fenced yard
and they bark at anything that happens within a 1/2 mile day or night.)
[...]been thinking about running a bunch of the piezoes in series and[...]

...and, you think that AGGRAVATING the animals FURTHER
will make them QUIET.

There are surely laws on the books where you are
which deal directly with irresponsible pet owners
and with noise abatement.
Make 2 telephone calls, first to the police then to Animal Control.
After the authorities are finished talking to the people,
have the cop give you a copy of the report
which includes the case number and name of the responding officer.

If the problem happens again,
make the calls again, this time using the previous case number.
Request that the same cop respond.
The people will be given a date to appear in court
where they will pay (in money and time) for their bad behavior.
Get a copy of the report on this incident as well.

If it happens a 3rd time,
reference the 2 previous reports and request that the dogs be removed.

There is a reason(s) why dogs bark.

It may be due to loneliness, exercise (lack of), etc., but usually NOT
to attract attention.

Being nice to the owner should be a tried, by advising about the dogs
getting a varying environment.

Yours sincererly

Steve

 

[John Fields]

On Mon, 25 Feb 2008 08:11:52 -0600, "Jon Slaughter"
<Jon_Slaughter@Hotmail.com> wrote:

"amdx" <amdx@knology.net> wrote in message
news:5fe78$47c2b7ac$18d6b40c$13581@KNOLOGY.NET...

"davidt" <dav1d@talktalk.net> wrote in message
news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...
I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will have
less turns if thicker wire. (it carries more current)


Only smaller wire because the current requirements are smaller. There is no
restriction on the wire size for a transformer except that it be able to
handle the current. (so it definitely could have been larger)

---
Sure, but since what a transformer does is transfer _power_ from one
winding to another, the product of current and voltage have to be
the same for both windings.

So, if the voltage in one winding is higher than in another, then
the current in the high-voltage winding _must_ be less than in the
low-voltage winding and it would be pointless to use wire with a
diameter more than that required to carry the current.

More precisely, for a lossless transformer:

Np Ep Is
---- = ---- = ----
Ns Es Ip

Where: Np is the number of turns on the primary,
Ns is the number of turns on the secondary,
Ep is the voltage impressed across the primary,
Es is the voltage induced across the secondary,
Ip is the current forced through the primary, and
Is is the current into the load

--
JF

 

[John Fields]

On Mon, 25 Feb 2008 02:18:54 -0800 (PST), harsha
<harshadxgroups@gmail.com> wrote:

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---
How about if I take the course and then pay you for it out of what
I'll be making by working for you under your job guarantee?

BTW, what does "(*Conditions apply)" mean?

--
JF

 

[Jamie]

davidt wrote:

I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?
The resistant you're measuring has nothing to do with the operation

of the transformer other than lowering its efficiency and Q. It's simply
a by product of the gauge wire used along with the length of wire used
for each winding.

The number of turns ratio between the Red windings and yellow windings
tells the whole story along with the gap spacing between them..

At this point, maybe you should reference some data from the net on
transformer theories.


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

 

[John Fields]

On Mon, 25 Feb 2008 19:40:06 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

davidt wrote:
I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?
The resistant you're measuring has nothing to do with the operation
of the transformer other than lowering its efficiency and Q. It's simply
a by product of the gauge wire used along with the length of wire used
for each winding.

The number of turns ratio between the Red windings and yellow windings
tells the whole story along with the gap spacing between them..

At this point, maybe you should reference some data from the net on
transformer theories.

---
Hmm... What theory would explain the "gap spacing" (???) between the
windings as a function of the turns ratio?

--
JF

 

[Jamie]

John Fields wrote:

On Mon, 25 Feb 2008 19:40:06 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


davidt wrote:

I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

The resistant you're measuring has nothing to do with the operation
of the transformer other than lowering its efficiency and Q. It's simply
a by product of the gauge wire used along with the length of wire used
for each winding.

The number of turns ratio between the Red windings and yellow windings
tells the whole story along with the gap spacing between them..

At this point, maybe you should reference some data from the net on
transformer theories.


---
Hmm... What theory would explain the "gap spacing" (???) between the
windings as a function of the turns ratio?

my point was short and simple. difference in current mode xformers and

potential types along with turn ratio's. also the construct of the
cores. With all this put together leads to PF (power factors), current
ratio's, form factor, wet/dry, efficiency etc..


Keeping it simple since the poster obviously needs to research some
transformer basics.


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

 

[Phil Allison]

"davidt"

I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.

** If it is from a 240 volt mains power supply, then the red wires are for
240 volts AC and the yellow ones are for 140 volts AC. The unit is rated
for about 75 VA.

If from a 120 volts supply, the yellow wires are for 70 volts AC and the
unit is rated for about 25 VA.


........ Phil

 

[Jon Slaughter]

"John Fields" <jfields@austininstruments.com> wrote in message
news:ssq5s3t2trdn67m2uosqt9ic55hn49b5hl@4ax.com...

On Mon, 25 Feb 2008 08:11:52 -0600, "Jon Slaughter"
Jon_Slaughter@Hotmail.com> wrote:


"amdx" <amdx@knology.net> wrote in message
news:5fe78$47c2b7ac$18d6b40c$13581@KNOLOGY.NET...

"davidt" <dav1d@talktalk.net> wrote in message
news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...
I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will
have
less turns if thicker wire. (it carries more current)


Only smaller wire because the current requirements are smaller. There is
no
restriction on the wire size for a transformer except that it be able to
handle the current. (so it definitely could have been larger)

---
Sure, but since what a transformer does is transfer _power_ from one
winding to another, the product of current and voltage have to be
the same for both windings.

So, if the voltage in one winding is higher than in another, then
the current in the high-voltage winding _must_ be less than in the
low-voltage winding and it would be pointless to use wire with a
diameter more than that required to carry the current.

More precisely, for a lossless transformer:

Np Ep Is
---- = ---- = ----
Ns Es Ip

Where: Np is the number of turns on the primary,
Ns is the number of turns on the secondary,
Ep is the voltage impressed across the primary,
Es is the voltage induced across the secondary,
Ip is the current forced through the primary, and
Is is the current into the load

And why not Np/Ns = D_Rs/D_Rp where D_Rx is the diameter? or even Np/Ns =
Rs/Rp?

The fact of the matter is that it doesn't matter as long as the as the wire
can carry the current(which essentially means heat dissipation).

You can use any wire size in any circumstance and its not *pointless*. It
depends on the application. True that you pretty never need a larger
diameter on the secondary than the primary in a step up... but potentially
there is still the possibility in certain applications. (such as if the
secondary happens to be in a much much hotter environment)

The idea transformer equations say nothing about the diameter's of the wire
used and for good reason. (not to mention that most wire sizes are
standardized)

So going off the restance or the diameter of the wire is by no means correct
and technically has nothing to do with a abstract ideal transformer. (I'm
not saying you can't use that relationship to find the optimal diameter for
a given number of turns but it is not necessary)

 

[John Fields]

On Tue, 26 Feb 2008 18:24:30 GMT, "Jon Slaughter"
<Jon_Slaughter@Hotmail.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:ssq5s3t2trdn67m2uosqt9ic55hn49b5hl@4ax.com...
On Mon, 25 Feb 2008 08:11:52 -0600, "Jon Slaughter"
Jon_Slaughter@Hotmail.com> wrote:


"amdx" <amdx@knology.net> wrote in message
news:5fe78$47c2b7ac$18d6b40c$13581@KNOLOGY.NET...

"davidt" <dav1d@talktalk.net> wrote in message
news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...
I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will
have
less turns if thicker wire. (it carries more current)


Only smaller wire because the current requirements are smaller. There is
no
restriction on the wire size for a transformer except that it be able to
handle the current. (so it definitely could have been larger)

---
Sure, but since what a transformer does is transfer _power_ from one
winding to another, the product of current and voltage have to be
the same for both windings.

So, if the voltage in one winding is higher than in another, then
the current in the high-voltage winding _must_ be less than in the
low-voltage winding and it would be pointless to use wire with a
diameter more than that required to carry the current.

More precisely, for a lossless transformer:

Np Ep Is
---- = ---- = ----
Ns Es Ip

Where: Np is the number of turns on the primary,
Ns is the number of turns on the secondary,
Ep is the voltage impressed across the primary,
Es is the voltage induced across the secondary,
Ip is the current forced through the primary, and
Is is the current into the load



And why not Np/Ns = D_Rs/D_Rp where D_Rx is the diameter? or even Np/Ns =
Rs/Rp?

---
Because the turns ratio has nothing to do with the resistance ratio.
---

The fact of the matter is that it doesn't matter as long as the as the wire
can carry the current(which essentially means heat dissipation).

---
Well, no. What _really_ matters is the resistance of the winding,
since that'll determine the voltage dropped across it, and that
voltage won't be able to be used by the load. While the I˛R losses
increase the winding's resistance, it's not usually enough to
matter much. For a clue, take a look at the temperature coefficient
of resistance of copper and translate that to the change in
resistance of a winding due to the change in temp. In any case, the
temp rise because of I˛R losses should be taken care of during the
design of the transformer and the proper wire size chosen to give
the desired regulation at that maximum temperature.
---

You can use any wire size in any circumstance and its not *pointless*.

---
You _cannot_ use any wire size in any application and expect the
application to work. For example, it would be pointless to wind a
secondary expected to supply 12 volts at 10 amperes with a single
strand of #40 AWG.
---

It depends on the application.

---
Precisely. And, for the transformer the OP was talking about,
(which he was using as a stepup transformer to get the results he
did) it would have been pointless to have wound the high-voltage
winding with larger diameter wire than the low-voltage winding.
---

True that you pretty never need a larger
diameter on the secondary than the primary in a step up... but potentially
there is still the possibility in certain applications. (such as if the
secondary happens to be in a much much hotter environment)

---
Like where??? You're grasping at straws.
---

The idea transformer equations say nothing about the diameter's of the wire
used and for good reason.

---
Then why did you ask, earlier: "And why not Np/Ns = D_Rs/D_Rp where
D_Rx is the diameter? or even Np/Ns = Rs/Rp?
---

(not to mention that most wire sizes are standardized)

---
And that has _what_ to do with anything???
---

So going off the restance or the diameter of the wire is by no means correct
and technically has nothing to do with a abstract ideal transformer. (I'm
not saying you can't use that relationship to find the optimal diameter for
a given number of turns but it is not necessary)

---
Slaughter, yer a fucking idiot!

--
JF

 

[Jon Slaughter]

"John Fields" <jfields@austininstruments.com> wrote in message
news:9iv8s39v98piqf4qsqv3ud7n3cu6p7kjf2@4ax.com...

On Tue, 26 Feb 2008 18:24:30 GMT, "Jon Slaughter"
Jon_Slaughter@Hotmail.com> wrote:


"John Fields" <jfields@austininstruments.com> wrote in message
news:ssq5s3t2trdn67m2uosqt9ic55hn49b5hl@4ax.com...
On Mon, 25 Feb 2008 08:11:52 -0600, "Jon Slaughter"
Jon_Slaughter@Hotmail.com> wrote:


"amdx" <amdx@knology.net> wrote in message
news:5fe78$47c2b7ac$18d6b40c$13581@KNOLOGY.NET...

"davidt" <dav1d@talktalk.net> wrote in message
news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...
I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got
a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will
have
less turns if thicker wire. (it carries more current)


Only smaller wire because the current requirements are smaller. There is
no
restriction on the wire size for a transformer except that it be able to
handle the current. (so it definitely could have been larger)

---
Sure, but since what a transformer does is transfer _power_ from one
winding to another, the product of current and voltage have to be
the same for both windings.

So, if the voltage in one winding is higher than in another, then
the current in the high-voltage winding _must_ be less than in the
low-voltage winding and it would be pointless to use wire with a
diameter more than that required to carry the current.

More precisely, for a lossless transformer:

Np Ep Is
---- = ---- = ----
Ns Es Ip

Where: Np is the number of turns on the primary,
Ns is the number of turns on the secondary,
Ep is the voltage impressed across the primary,
Es is the voltage induced across the secondary,
Ip is the current forced through the primary, and
Is is the current into the load



And why not Np/Ns = D_Rs/D_Rp where D_Rx is the diameter? or even Np/Ns =
Rs/Rp?

---
Because the turns ratio has nothing to do with the resistance ratio.
---

The fact of the matter is that it doesn't matter as long as the as the
wire
can carry the current(which essentially means heat dissipation).

---
Well, no. What _really_ matters is the resistance of the winding,
since that'll determine the voltage dropped across it, and that
voltage won't be able to be used by the load. While the I˛R losses
increase the winding's resistance, it's not usually enough to
matter much. For a clue, take a look at the temperature coefficient
of resistance of copper and translate that to the change in
resistance of a winding due to the change in temp. In any case, the
temp rise because of I˛R losses should be taken care of during the
design of the transformer and the proper wire size chosen to give
the desired regulation at that maximum temperature.
---

You can use any wire size in any circumstance and its not *pointless*.

---
You _cannot_ use any wire size in any application and expect the
application to work. For example, it would be pointless to wind a
secondary expected to supply 12 volts at 10 amperes with a single
strand of #40 AWG.
---

It depends on the application.

---
Precisely. And, for the transformer the OP was talking about,
(which he was using as a stepup transformer to get the results he
did) it would have been pointless to have wound the high-voltage
winding with larger diameter wire than the low-voltage winding.

No! Why you think he is winding anything? They are already wound and it was
wound for a specific application. In general you are correct in that for a
step up the wire diameter will be smaller because there is less current. The
point I'm trying to make is that it is not a necessary or sufficient
requirement for step up transformers. maybe in 99.999% of transfomers it
will hold but even then there is no "formula" to calculate the diameter of
the secondary from the primary or vice versa.


I could easily make a transformer that would violate your "principle" and it
would work fine! Sure it might be cost or space inefficient but the
tranformer itself doesn't care.

Now you say "Well if its too small then it will over heat"!! This has
nothing to do with basic ideal transformer theory which says nothing about
wire's resistances or anything. Hell, if I wanted I could then just use
super conducting material and use infinitely thin wire on both sides!!

---

True that you pretty never need a larger
diameter on the secondary than the primary in a step up... but potentially
there is still the possibility in certain applications. (such as if the
secondary happens to be in a much much hotter environment)

---
Like where??? You're grasping at straws.

I think thats what you are doing. You are trying to make the OP think that
the diameter matters and gives a good approximation to the turns ratio and
it doesn't. Go take a transformer and measure the diameters then take the
ratio and I bet you won't get a good approximation to the turns ratio! I
DARE YOU!

Since I know you are chicken I did it for you. I have a tranformer on my
desk. Its a step down from 120:12(approximately) so its about 10:1.

The diameter of the primary is 100mil, the diameter of the secondary is 40
mil.... hmmm, is this 10:1 or 1:10? not even close!


Of course now you will claim that the person who made the transformer is
nutz and has no clue about transformer design.

---

The idea transformer equations say nothing about the diameter's of the
wire
used and for good reason.

---
Then why did you ask, earlier: "And why not Np/Ns = D_Rs/D_Rp where
D_Rx is the diameter? or even Np/Ns = Rs/Rp?
---

WTF? I asked why that isn't shown in the books... I'm ASKING you why that
isn't true because you are essentially claiming it is. Thats why I have
question marks there.

(not to mention that most wire sizes are standardized)

---
And that has _what_ to do with anything???
---

Forget it... I can see this is a lost cause.

So going off the restance or the diameter of the wire is by no means
correct
and technically has nothing to do with a abstract ideal transformer. (I'm
not saying you can't use that relationship to find the optimal diameter
for
a given number of turns but it is not necessary)

---
Slaughter, yer a fucking idiot!
--
JF

Damn, I really thought I put you on my ignore list... along with the other
morons. Well, you won't escape this time.

 

[John Fields]

On Wed, 27 Feb 2008 01:35:59 GMT, "Jon Slaughter"
<Jon_Slaughter@Hotmail.com> wrote:

Damn, I really thought I put you on my ignore list... along with the other
morons.

---
You mean those of your ilk have _all_ plonked me?
---

Well, you won't escape this time.

---
Escape, hell... I'd volunteer!

But, if you've plonked me, how do you expect to be able to read the
answers to your dumbass questions?

--
JF

 

[ShamShoon]

On Feb 27, 12:24 am, Bill Bowden <wrongaddr...@att.net> wrote:

ohm speaker and 5K emitter resistor. How can you ever get much
current, or power through a 8 ohm speaker in series with a 5K
resistor? Might work at 200 volts.

AoE stated that the output impedance of an emitter follower is almost
independent of the emitter resistor. It's hard for me to think of
another model in which the 5k plays a role. Perhaps a voltage source
in series with a diode then the source & diode combo in parallel with
5k & 8Ohm resistors.

Solution is to use a transformer in place of the 5K resistor and bias
the stage so the idle current and supply voltage represents about
twice the output power. Or, maybe that's 4 times the power, I forget.

How do I know the output power? The speaker I want to drive?

Anyway, for a 1 watt output using a 6 volt supply, the bias current
will be somewhere around 500mA.

Could you elaborate on how you came up with this value? I'm thinking
the transformer would make and impedance transformation and so the 8
Ohm across the secondary would appear higher across the primary, and
current will drop. 500mA sounds to me like a very high current.

The transistor will dissipate most all the voltage times the current, or maybe 3 watts, so you need a heat
sink. The secondary of the transformer is connected to the speaker.
It's called a 'class A' amplifier and has very good audio quality.
Play around with the bias current to see how much power you can get
out.

-Bill