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'[OT] what does Center Top mean'
1998\12\11@201720 by Shahid Sheikh

picon face
This is completely OT but dont know where else to ask. I need to buy a
transformer with a 12V 8A secondary and looking at the Newark catalog, I
have transformers that have "C.T." written next to the secondary voltage.
In the footnotes it says that C.T. stands for Center Top. Anyone knows what
Centor Top means? And now that I have already wasted bandwidth, anyone
knows of a cheap source for transformers?

Shahid

1998\12\11@204457 by David W. Duley

picon face
In a message dated 12/11/98 5:17:32 PM Pacific Standard Time, spam_OUTSheikhTakeThisOuTspamEROLS.COM
writes:

<<
This is completely OT but dont know where else to ask. I need to buy a
transformer with a 12V 8A secondary and looking at the Newark catalog, I
have transformers that have "C.T." written next to the secondary voltage.
In the footnotes it says that C.T. stands for Center Top. Anyone knows what
Centor Top means? And now that I have already wasted bandwidth, anyone
knows of a cheap source for transformers?

Shahid

 >>

Hi Shahid,

If your docs say Center Top then its a typo.  The correct phrase should be
"Center Tap".
This is a tap (or a wire attached to) the center of the seconday winding of
the transformer.  If a transformer is labeled 25VCT, then you will get 25
volts between the outer two leads and 12.5 volts between the center tap and
either of the outer leads.  This is conveniant to get multiple voltages or can
be used in two diode full wave rectifiers to produce DC from the AC that comes
out of the transformer.

Hope this helps
Dave Duley

1998\12\11@204504 by Sean Breheny

face picon face
Hi Shahid,

       C.T. stands for "Center Tap" not "Center Top". It means that the seconda
ry
is divided into two sections, and there are three wires attached to it: one
for each end and one for the middle. connecting between the two end wires
will give you the full voltage (12v in this case) and connecting between an
end wire and the middle will give you half the voltage(6v in this case).

       I have had luck with cheap transformers from Marlin P. Jones Associates,
at http://www.mpja.com I recently bought two 24v C.T., 4 amp transformers
for $8.49 each. Ones for less current are much cheaper.

Good luck,

Sean

At 08:01 PM 12/11/98 -0500, you wrote:
>This is completely OT but dont know where else to ask. I need to buy a
>transformer with a 12V 8A secondary and looking at the Newark catalog, I
>have transformers that have "C.T." written next to the secondary voltage.
>In the footnotes it says that C.T. stands for Center Top. Anyone knows what
>Centor Top means? And now that I have already wasted bandwidth, anyone
>knows of a cheap source for transformers?
>
>Shahid
>
+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam@spam@cornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\12\12@052623 by Mark Willis

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face
Rumor has it that one thing to be aware of when looking at some
cheaper transformers, is that some of the really really cheap ones don't
use proper iron for the transformer cores - they use aluminum instead.
This may be just baloney, of may be just audio transformers (I know it's
a rumor, at least.)  Anyone know anything more than that on this
subject?

 (The problem - if so - is that eddy losses in aluminum mean heat,
inefficiency, and so on;  Problem I have with the rumor is that, last
*I* priced 'em, iron was cheaper than aluminum, I thought?  Harder to
die cut, though.  I'm not a transformer expert, bet there's one or more
on this list!)

 Mark, mwillisspamKILLspamnwlink.com

Shahid Sheikh wrote:
>
> This is completely OT but dont know where else to ask. I need to buy a
> transformer with a 12V 8A secondary and looking at the Newark catalog, I
> have transformers that have "C.T." written next to the secondary voltage.
> In the footnotes it says that C.T. stands for Center Top. Anyone knows what
> Centor Top means? And now that I have already wasted bandwidth, anyone
> knows of a cheap source for transformers?
>
> Shahid

1998\12\13@134739 by Peter L. Peres

picon face
On Sat, 12 Dec 1998, Mark Willis wrote:

> Rumor has it that one thing to be aware of when looking at some
> cheaper transformers, is that some of the really really cheap ones don't
> use proper iron for the transformer cores - they use aluminum instead.
> This may be just baloney, of may be just audio transformers (I know it's
> a rumor, at least.)  Anyone know anything more than that on this
> subject?

imho, change the source of the rumor. Aluminium is slightly diamagnetic so
you CAN'T make cores with it, unless you make an enclosure for a coreless
transformer for it, and are trying to keep the field inside (but they are
bad even at this, unless very thick). Just in case you wonder: those Al
cores in UHF coils *lower* the inductance when screwed in deeper. They
also lower the Q for which reason they seem to have disappeared from
modern equipment.

Peter

1998\12\14@000425 by Mark Willis

flavicon
face
Could well be that he was talking aluminum wires (I was talking to
someone else, I'll ask the source next time I catch him and ask for more
info.)  He's an audio electronics fanatic I know, heavily into tubes as
well.  (I was talking hard drives to someone else just before he started
talking to the person I drove there about the aluminum whatever.  I
could have totally misheard, he's sorta hard to catch; whatever <G>)

 Mark, .....mwillisKILLspamspam.....nwlink.com

Peter L. Peres wrote:
{Quote hidden}

1998\12\14@115213 by David W. Duley

picon face
In a message dated 12/12/98 2:26:28 AM Pacific Standard Time,
EraseMEmwillisspam_OUTspamTakeThisOuTNWLINK.COM writes:

<<
Rumor has it that one thing to be aware of when looking at some
cheaper transformers, is that some of the really really cheap ones don't
use proper iron for the transformer cores - they use aluminum instead.
This may be just baloney, of may be just audio transformers (I know it's
a rumor, at least.)  Anyone know anything more than that on this
subject?

  (The problem - if so - is that eddy losses in aluminum mean heat,
inefficiency, and so on;  Problem I have with the rumor is that, last
*I* priced 'em, iron was cheaper than aluminum, I thought?  Harder to
die cut, though.  I'm not a transformer expert, bet there's one or more
on this list!)

  Mark, mwillisspamspam_OUTnwlink.com

Shahid Sheikh wrote:
> >>
Hi Mark,
I find this a little hard to belive.  I don't think I have ever seen an
aluminum core in a transformer.  I can't see how this would be cheaper.
Aluminum costs about 40 cents a pound, Iron is about $12.00 a ton.  I think
that if transformer makers could get away with it they would use aluminum for
the weight savings.  Thats why Aircraft transformers operate at higher
frequencies (400hz) so they can do the same work with smaller and lighter
cores.

Best Regards
Dave Duley

1998\12\14@120046 by Jochen Feldhaar

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face
Hello David,

there is an area where aluminum conductors were (not anymore) commonplace,
and this is the former German "Democratic" Republic. Because Copper was
extremely expensive and they had to pay in hard (...western...) currency
for this, so they used the aluminum they had themselves. It resulted in
bigger thickness of the conductors, although somewhat less weight.
Especially awkward were the aluminum cables for common house installations,
they were b**ches to bend or put around corners.
So in some other "east European" states there may still be the one or other
company around that makes these aluminum wires and cables.
As some wholesale warehouses bought in the former GDR for use in Western
Germany (also former), all over Germany these things can be found...

Greetings,

Jochen DH6FAZ
@spam@jfKILLspamspamdetektor.de

1998\12\14@121306 by dave vanhorn

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At 11:50 AM 12/14/98 -0500, David W. Duley wrote:
{Quote hidden}

Never seen aluminum in a transformer, except as a tuning slug.
Aluminum as a core material is not going to happen, and the fad for
aluminum wire was limited to the 110V wiring crowd. (How would you
terminate to it?)

>   (The problem - if so - is that eddy losses in aluminum mean heat,
> inefficiency, and so on;  Problem I have with the rumor is that, last
> *I* priced 'em, iron was cheaper than aluminum, I thought?  Harder to
> die cut, though.  I'm not a transformer expert, bet there's one or more
> on this list!)

We ran into that too, we converted a baseplate design from steel to aluminum.
The vendor came back to us in a panic, "aluminum is THREE TIMES as
expensive as steel!!"
It sure is, they price it by the pound.  In linear feet of a given
thickness, it's about the same.



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1998\12\14@121924 by dave vanhorn

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At 06:00 PM 12/14/98 +0100, Jochen Feldhaar wrote:
>Hello David,
>
>there is an area where aluminum conductors were (not anymore) commonplace,
>and this is the former German "Democratic" Republic.

This happened in the US as well, during the late '70s IIRC. We discovered
that aluminum was a BAD idea in house or industrial wiring, as it oxidizes,
and has higher resistance than copper, which electricians seemed prone to
forget.

Still, I don't think there's ever been a transformer wound with aluminum
wire. I can't imagine that it would take the bending and forming wire in
that small a gage would be quite interesting.

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1998\12\14@123822 by Peter L. Peres

picon face
Nobody said small transformers were wound with Al. Al is not very ductile
and it cracks when bent around small radiuses. However, physics people
seem to like the idea of a non-magnetic free-standing Al pipe coil (air or
vacuum core, large dia.) especially since one can run cooling water
through it.

Also certain antenna matching transformers and coils (coreless, large) are
also made of Al, free-standing, afaik.

Peter

1998\12\14@124228 by David W. Duley

picon face
In a message dated 12/14/98 9:19:30 AM Pacific Standard Time,
RemoveMEdvanhornTakeThisOuTspamCEDAR.NET writes:

<<
This happened in the US as well, during the late '70s IIRC. We discovered
that aluminum was a BAD idea in house or industrial wiring, as it oxidizes,
and has higher resistance than copper, which electricians seemed prone to
forget.
 >>

Hi All,

This isn't quite right.  The reason Aluminum wiring was a bad idea is because
the fittings that are used are typically copper.  Coper and Aluminum have
different thermal expansion coeficients.  The fittings eventually loosen up
and then you have arcing and fire hazard.  Special fittings were required.
The problem came from mixing up the fittings or using fitting that were
intended for copper.

Best regards
Dave Duley

1998\12\18@085121 by paulb

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face
Peter L. Peres wrote:

> Also certain antenna matching transformers and coils (coreless, large)
> are also made of Al, free-standing, afaik.

 And in case this isn't stunningly evident, the vast majority of TV
antennae!
--
 Cheers,
       Paul B.

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