35amp tranformer wanted

[Karl Shoemaker]

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg
Thanks !!

 

[Larry Brasfield]

"Karl Shoemaker" <wa7ycp@yahoo.com> wrote in message news:4273B43A.18D467A9@yahoo.com...

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me.

For your 25 A DC current requirement, you should have a
transformer with 45 A RMS rating unless you have some
real smoothing inductance in your rectifier/capacitor circuit.

Here is a vendor I've used for small quantity orders:
http://www.tierneytransformer.com/quote.cfm

If you have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

Post here, read here. That's the Usenet way.

Thanks !!
Welcome.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Pooh Bear]

Karl Shoemaker wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me.

How did you search on the web ?

Your requiremnt for a 400VA approx transformer seems pretty undemanding.
I'm sure there are lots of sources. The *10V* isn't likely to be very
standard though as you've found out.

Tried looking here ?

http://www.mouser.com/?Ne=601&handler=data.listcategory&Ntt=*transformer*&terms=transformer&crc=true&N=142&Ns=SField

Btw - it's common practice to return to the newsgroup to read the replies
*not* to ask ppl to email you. That's not the way newsgroups are meant to
work - they're meant to be for the benefit of all.

Emailed in this instance only as explanation.


Graham

 

[Pooh Bear]

Karl Shoemaker wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me.

How did you search on the web ?

Your requiremnt for a 400VA approx transformer seems pretty undemanding.
I'm sure there are lots of sources. The *10V* isn't likely to be very
standard though as you've found out.

Tried looking here ?

http://www.mouser.com/?Ne=601&handler=data.listcategory&Ntt=*transformer*&terms=transformer&crc=true&N=142&Ns=SField

Btw - it's common practice to return to the newsgroup to read the replies
*not* to ask ppl to email you. That's not the way newsgroups are meant to
work - they're meant to be for the benefit of all.


Graham

 

[John Fields]

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com>
wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf

--
John Fields
Professional Circuit Designer

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:kgk77150n37ski7ksmani9cae7k3ij9u6f@4ax.com...

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com
wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf

That's a good tip, as to vendor. However, for DC supplies
that will "pull around 20-25 amps", the secondary RMS
current rating should be somewhat higher, by a factor
related to rectifier conduction angle. A typical value,
for a transformer with 16% load regulation, is a factor
of 1.8, meaning you would need a 45 A RMS rating.
(This issue is briefly covered in the back of the Signal
catalog.) For that reason, the 10-50 would be a better
selection for your application, using the secondary
windings in series. (In parallel, you would get 5 VAC,
which the catalog shows as "5VCT" for some reason.)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[John Fields]

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com>
wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

---
There's a 4-50-4010 or a 4-50-4020, which is a little closer to what
you need, at:

http://www.mcitransformer.com/i_4-50.html

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com>
wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

---
Googling for 430-7001 gets a hit at:

http://www.shopatex.com/shop/index.php?cPath=68

Which looks like exactly what you want.

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Sat, 30 Apr 2005 12:12:24 -0700, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:kgk77150n37ski7ksmani9cae7k3ij9u6f@4ax.com...
On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com
wrote:

I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf


That's a good tip, as to vendor. However, for DC supplies
that will "pull around 20-25 amps", the secondary RMS
current rating should be somewhat higher, by a factor
related to rectifier conduction angle. A typical value,
for a transformer with 16% load regulation, is a factor
of 1.8, meaning you would need a 45 A RMS rating.
(This issue is briefly covered in the back of the Signal
catalog.) For that reason, the 10-50 would be a better
selection for your application, using the secondary
windings in series. (In parallel, you would get 5 VAC,
which the catalog shows as "5VCT" for some reason.)

---
Yes, that 10-25 was a transcription error. Since the OP asked for
something which obviously works for him and currently can deliver 35
amps, it's not likely that he'd be happy with something which can only
supply 25.

The reason the catalog shows it as "5VCT" is because the secondaries
are center tapped and, if the windings are connected in parallel, the
center taps will also be in parallel. If connected in series, of
course, the "center tap" will be the junction of the windings.

Scroll down to page 2 or 3 of the PDF (page 25 or 26 of the catalog)
for the wiring diagrams.

--
John Fields
Professional Circuit Designer

 

[Fred Bloggs]

Larry Brasfield wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:kgk77150n37ski7ksmani9cae7k3ij9u6f@4ax.com...

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com
wrote:


I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg

---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf



That's a good tip, as to vendor. However, for DC supplies
that will "pull around 20-25 amps", the secondary RMS
current rating should be somewhat higher,...

Who says that "20-25" amps is DC?- Why not RMS? And who says the duty is
continuous? Why not intermittent? You seem to be falling on your ass for
the umpteenth time.

You seem to have latched on to some elementary factoring and now you try
to create another stench , overlooking the OP's past successful
experience with that rating, i.e. ignoring given information. One
wonders what kind of "engineer" you could be when your comprehension
limits at <1%.

 

[Larry Brasfield]

[Derf transform applied.]

"Fred Bloggs" <nospam@nospam.com> wrote in
message news:42740BE5.7040305@nospam.com...

Larry Brasfield wrote:
"John Fields" <jfields@austininstruments.com> wrote in message
news:kgk77150n37ski7ksmani9cae7k3ij9u6f@4ax.com...

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com
wrote:


I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg
---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf

That's a good tip, as to vendor. However, for DC supplies
that will "pull around 20-25 amps", the secondary RMS
current rating should be somewhat higher,...

Who says that "20-25" amps is DC?- Why not RMS?

Most equipment that would be called "transmitter"
runs off of DC. The term "power supply" is most
often used to refer to a DC supply. Because the
OP uses different terms, "transformers" and "power
supplies", it is a fair assumption that he uses them
for different referents. His use of "they" in the 2nd
sentence most likely refers to the antecedant most
immediately preceding, according to the construction
rules most normal people understand, so reading his
"20-25 amps" as being the DC transmitter load is the
most reasonable interpretation.

It may be that accidents of intermittent usage have
allowed the OP to not see lifetimes shortened so
much as to suspect an under-rated transformer.

overlooking the OP's past successful experience with that rating, i.e. ignoring given information.

There is scant evidence that his experience has actually
been successful. For all we can tell, he is now trying to
obtain a replacement for a failed device. Repeaters are
often subject to harsh environments, and recommending
less of a transformer than the OP appears to need would
be irresponsible.

The OP is, of course, free to take his intermittent usage
and possibly benign environment into consideration.
The ratio of RMS to DC current that I mentioned will
be useful whether he uses it to directly obtain a required
current rating or applies some anti-derating to determine
what he really needs.

There is little danger of the OP being misled by my post,
where my interpretation of his post was reasonably clear.
So I have to conclude that Fred is just adding noise for
his usual disgusting reasons.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Larry Brasfield]

"Fred Bloggs" <nospam@nospam.com> wrote in message
news:42745755.3050204@nospam.com...

Larry Brasfield wrote:

["Bloggs" had asked the following:]
Who says that "20-25" amps is DC?- Why not RMS?

Most equipment that ... [..snip drivel...]

Could be- but also may have been inferred from a line reading- only an idiot like you could be certain of the meaning.

Fascinating how you cut the reasoning behind my
answer to your question, then comment upon it in
a derogatory manner. You make clear that you
are unable or unwilling to deal with the substance
of your issue, preferring name-calling instead.

It may be that accidents of intermittent usage have
allowed the OP to not see lifetimes shortened so
much as to suspect an under-rated transformer.

Nah- another crock- the usual current rating is specified for a core temp rise of 40oC- maybe his environment makes the 35A
reliable- except to a few idiots like yourself. 35/20=1.75 and this is right on the worst case RMS/DC when the load draws 20A DC
which is the OP's range.

Your speculation is no more factual than mine. The
difference is that you would err toward lower margin,
whereas my recommendation, if wrong at all, errs
toward higher margin. Also lost in the draft here is
the fact that the part I recommended was the next
largest size available from Signal beyond one that is
clearly marginal.

overlooking the OP's past successful experience with that rating, i.e. ignoring given information.

There is scant evidence that his experience has actually
been successful. For all we can tell, he is now trying to
obtain a replacement for a failed device. Repeaters are
often subject to harsh environments, and recommending
less of a transformer than the OP appears to need would
be irresponsible.

But you don't know if he is using an inductor filter off the rectifier, then it would be very conservatively acceptable.

I mentioned that possibility in my post. Having cut it,
you look foolish bringing it up now as your idea.

Also, the OP said nothing about any failure, it was more that he wanted to build more of the power supplies, wherein he is
rewinding the secondaries: "I build 10-11 volt power supplies for my repeater's transmitters. Since they pull around 20-25 amps
I've been using 35 amp/12v rated transformers and
pulling a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of these and I'd like to get at least one more." Does
that say anything about failures? It sounds like he wants to build additional power supplies.

There is room for many different scenarios within the
OP's description. Is is your insistence on certainty
about your interpretation that is awry here.

....

There is little danger of the OP being misled by my post,
where my interpretation of his post was reasonably clear.
So I have to conclude that Fred is just adding noise for
his usual disgusting reasons.

It is important that the OP understand you are a crock of manure- all of your posts are pure noise- you have nothing but
irrelevant questions about some elementary aspect of application that you never follow through on.

I'm sure the OP will form his own judgement, with due
consideration of your ability to evaluate character. I
urge him to read your other posts to help in that regard.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Fred Bloggs]

Larry Brasfield wrote:

"Fred Bloggs" <nospam@nospam.com> wrote in message
news:42745755.3050204@nospam.com...

Larry Brasfield wrote:


["Bloggs" had asked the following:]

Who says that "20-25" amps is DC?- Why not RMS?

Most equipment that ... [..snip drivel...]

Could be- but also may have been inferred from a line reading- only an idiot like you could be certain of the meaning.


Fascinating how you cut the reasoning behind my
answer to your question, then comment upon it in
a derogatory manner. You make clear that you
are unable or unwilling to deal with the substance
of your issue, preferring name-calling instead.

Nah- the idea is that everything you say is easily challenged, the name
calling follows naturally from your aggravating and gargantuan level of
stupidity.

And who says the duty is continuous? Why not intermittent? [derf]

It may be that accidents of intermittent usage have
allowed the OP to not see lifetimes shortened so
much as to suspect an under-rated transformer.

Nah- another crock- the usual current rating is specified for a core temp rise of 40oC- maybe his environment makes the 35A
reliable- except to a few idiots like yourself. 35/20=1.75 and this is right on the worst case RMS/DC when the load draws 20A DC
which is the OP's range.


Your speculation is no more factual than mine.

Not really- the OP said 20-25 amp range....

The
difference is that you would err toward lower margin,
whereas my recommendation, if wrong at all, errs
toward higher margin. Also lost in the draft here is
the fact that the part I recommended was the next
largest size available from Signal beyond one that is
clearly marginal.

[...snip more drivel...]

I'm sure the OP will form his own judgement, with due
consideration of your ability to evaluate character. I
urge him to read your other posts to help in that regard.

Yeah- well I "urge" him to read your bullsh_t posts, then he can see
your character and competence problems.

 

[John Fields]

On Sat, 30 Apr 2005 16:20:05 -0700, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"Fred Bloggs" <nospam@nospam.com> wrote in
message news:42740BE5.7040305@nospam.com...
Larry Brasfield wrote:
"John Fields" <jfields@austininstruments.com> wrote in message
news:kgk77150n37ski7ksmani9cae7k3ij9u6f@4ax.com...

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com
wrote:


I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg
---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf

That's a good tip, as to vendor. However, for DC supplies
that will "pull around 20-25 amps", the secondary RMS
current rating should be somewhat higher,...

Who says that "20-25" amps is DC?- Why not RMS?

Most equipment that would be called "transmitter"
runs off of DC. The term "power supply" is most
often used to refer to a DC supply. Because the
OP uses different terms, "transformers" and "power
supplies", it is a fair assumption that he uses them
for different referents. His use of "they" in the 2nd
sentence most likely refers to the antecedant most
immediately preceding, according to the construction
rules most normal people understand, so reading his
"20-25 amps" as being the DC transmitter load is the
most reasonable interpretation.

And who says the duty is continuous? Why not intermittent? [derf]

It may be that accidents of intermittent usage have
allowed the OP to not see lifetimes shortened so
much as to suspect an under-rated transformer.

You [derf] overlooking the OP's past successful experience with that rating, i.e. ignoring given information.

There is scant evidence that his experience has actually
been successful. For all we can tell, he is now trying to
obtain a replacement for a failed device. Repeaters are
often subject to harsh environments, and recommending
less of a transformer than the OP appears to need would
be irresponsible.

The OP is, of course, free to take his intermittent usage
and possibly benign environment into consideration.
The ratio of RMS to DC current that I mentioned will
be useful whether he uses it to directly obtain a required
current rating or applies some anti-derating to determine
what he really needs.

There is little danger of the OP being misled by my post,
where my interpretation of his post was reasonably clear.
So I have to conclude that Fred is just adding noise for
his usual disgusting reasons.

---
I disagree. Since the OP didn't explicitly state that he's having any
problems other than locating a transformer, There is _no_ evidence
that the OP is having any trouble at all with his setup. On the
contrary, he stated that he builds power supplies for his repeaters,
(note the plural) and his removing turns from the secondary of a
normally easily obtainable (and inexpensive) transformer indicates
that he knows what he's doing and is tailoring the transformer's
output voltage to just what he needs to run his repeaters.
Furthermore, your intimation that there is scant evidence that the
OP's experience has been successful is insulting and insinuates that
the OP _doesn't_ know what he's doing. You have no idea how his
repeaters are configured and, consequently, your assumptions about
"accidents of intermittent usage" are presumptuous. In addition, you
know nothing about how well the transformer regulates, or what the
input to the filter looks like, so your 'advice' is specious and seems
to be designed for the purpose of castigating instead of helping.

--
John Fields
Professional Circuit Designer

 

[John Woodgate]

I read in sci.electronics.design that John Fields
<jfields@austininstruments.com> wrote (in
<2hp9711s326d1544d5vi3iqkmjpahqnuo3@4ax.com&gt about '35amp tranformer
wanted', on Sun, 1 May 2005:

I disagree.

I think anyone who joins the private fight between Bloggs and Brasfield
has more valour than discretion.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:2hp9711s326d1544d5vi3iqkmjpahqnuo3@4ax.com...

On Sat, 30 Apr 2005 16:20:05 -0700, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

[Derf transform applied.]

"Fred Bloggs" <nospam@nospam.com> wrote in
message news:42740BE5.7040305@nospam.com...
Larry Brasfield wrote:
"John Fields" <jfields@austininstruments.com> wrote in message
news:kgk77150n37ski7ksmani9cae7k3ij9u6f@4ax.com...

On Sat, 30 Apr 2005 09:37:14 -0700, Karl Shoemaker <wa7ycp@yahoo.com
wrote:


I build 10-11 volt power supplies for my repeater's transmitters. Since
they pull
around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling
a few windings off to get 10 volts AC. The vender (Hosfelt) ran out of
these and I'd like to get at least one more. The part numbers and other
lables on the transformer are:
430-7001-4, EIA 6-9534, CLASS 180 H1 MEXICO. They are about 4 1/2" x
4", etc. Searcing on the web did not bring any current items to me. If
you
have any leads please email me wa7ycp@yahoo.com or visit my site
http://www.dalek.org/srg
---
Check out a P/N 10-25 with parallel secondaries at:

http://www.belfuse.com/Data/DBObject/pgs24_26.pdf

That's a good tip, as to vendor. However, for DC supplies
that will "pull around 20-25 amps", the secondary RMS
current rating should be somewhat higher,...

Who says that "20-25" amps is DC?- Why not RMS?

Most equipment that would be called "transmitter"
runs off of DC. The term "power supply" is most
often used to refer to a DC supply. Because the
OP uses different terms, "transformers" and "power
supplies", it is a fair assumption that he uses them
for different referents. His use of "they" in the 2nd
sentence most likely refers to the antecedant most
immediately preceding, according to the construction
rules most normal people understand, so reading his
"20-25 amps" as being the DC transmitter load is the
most reasonable interpretation.

And who says the duty is continuous? Why not intermittent? [derf]

It may be that accidents of intermittent usage have
allowed the OP to not see lifetimes shortened so
much as to suspect an under-rated transformer.

You [derf] overlooking the OP's past successful experience with that rating, i.e. ignoring given information.

There is scant evidence that his experience has actually
been successful. For all we can tell, he is now trying to
obtain a replacement for a failed device. Repeaters are
often subject to harsh environments, and recommending
less of a transformer than the OP appears to need would
be irresponsible.

The OP is, of course, free to take his intermittent usage
and possibly benign environment into consideration.
The ratio of RMS to DC current that I mentioned will
be useful whether he uses it to directly obtain a required
current rating or applies some anti-derating to determine
what he really needs.

There is little danger of the OP being misled by my post,
where my interpretation of his post was reasonably clear.
So I have to conclude that Fred is just adding noise for
his usual disgusting reasons.

---
I disagree.

Puzzling.

Since the OP didn't explicitly state that he's having any
problems other than locating a transformer, There is _no_ evidence
that the OP is having any trouble at all with his setup.

True. Did you notice that I preceded that possibility
with "For all we can tell,"?

On the
contrary, he stated that he builds power supplies for his repeaters,
(note the plural) and his removing turns from the secondary of a
normally easily obtainable (and inexpensive) transformer indicates
that he knows what he's doing and is tailoring the transformer's
output voltage to just what he needs to run his repeaters.

Hence the technical level at which I responded. I have
not assumed the OP to lack any basic technical skills.

Furthermore, your intimation that there is scant evidence that the
OP's experience has been successful is insulting and insinuates that
the OP _doesn't_ know what he's doing.

I must disagree with that conclusion. It is illogical and
false. My statement about evidence is no more than a
statement about the evidence. And as you well know,
all humans can overlook something or be mistaken.
My implication that the OP might have exceeded the
RMS current rating of his transformer does not diminish
my respect for people who build their own equipment.

You have no idea how his
repeaters are configured and, consequently, your assumptions about
"accidents of intermittent usage" are presumptuous.

My statement about that was in answer to Fred's
suggestion that RMS current beyond the rating
could be fine. Anytime one relies on a less than
100% duty cycle and limited durations to avoid
problems with power handling capability that is
not good for continuous use, one is exposed to
accidents of usage. For a repeater, for example,
the average power may be fine during a normal
conversation, but not during a long download or
upload when the channel is used with a modem.

Furthermore, I have made no assumptions at all
about "accidents of intermittent usage".

In addition, you
know nothing about how well the transformer regulates, or what the
input to the filter looks like, so your 'advice' is specious

I know something of the input filter from the output
voltage spec and the input voltage spec. Enough to
know that the conduction angle is not very far off
the limiting case of large filter capacitance. As for
the regulation, I stated my assumption about that,
so the OP is perfectly able to see if it applies and
ask how it changes the result if not.

and seems
to be designed for the purpose of castigating instead of helping.

Your speculation about my motive is incorrect.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[John Fields]

On Sun, 1 May 2005 16:38:43 +0100, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that John Fields
jfields@austininstruments.com> wrote (in
2hp9711s326d1544d5vi3iqkmjpahqnuo3@4ax.com&gt about '35amp tranformer
wanted', on Sun, 1 May 2005:

I disagree.

I think anyone who joins the private fight between Bloggs and Brasfield
has more valour than discretion.

---
I agree.


--
John Fields
Professional Circuit Designer

 

[Rich Grise]

On Sun, 01 May 2005 16:38:43 +0100, John Woodgate wrote:

I read in sci.electronics.design that John Fields
jfields@austininstruments.com> wrote (in
2hp9711s326d1544d5vi3iqkmjpahqnuo3@4ax.com&gt about '35amp tranformer
wanted', on Sun, 1 May 2005:

I disagree.

I think anyone who joins the private fight between Bloggs and Brasfield
has more valour than discretion.

<AOL>
Me Too!
</AOL>

;-)

 

[keith]

On Sun, 01 May 2005 16:38:43 +0100, John Woodgate wrote:

I read in sci.electronics.design that John Fields
jfields@austininstruments.com> wrote (in
2hp9711s326d1544d5vi3iqkmjpahqnuo3@4ax.com&gt about '35amp tranformer
wanted', on Sun, 1 May 2005:

I disagree.

I think anyone who joins the private fight between Bloggs and Brasfield
has more valour than discretion.

Valor? (UKUS spelling accepted) I usually consider valor a positive
attribute. Of course discresion is too, but that too doesn't compute with
Bloggs and Brasfield.

--
Keith

 

[Fred Bloggs]

Larry Brasfield wrote:

Who says that "20-25" amps is DC?- Why not RMS?


Most equipment that ... [..snip drivel...]

Could be- but also may have been inferred from a line reading- only an
idiot like you could be certain of the meaning.

And who says the duty is continuous? Why not intermittent? [derf]


It may be that accidents of intermittent usage have
allowed the OP to not see lifetimes shortened so
much as to suspect an under-rated transformer.

Nah- another crock- the usual current rating is specified for a core
temp rise of 40oC- maybe his environment makes the 35A reliable- except
to a few idiots like yourself. 35/20=1.75 and this is right on the worst
case RMS/DC when the load draws 20A DC which is the OP's range.

You [derf] overlooking the OP's past successful experience with that rating, i.e. ignoring given information.


There is scant evidence that his experience has actually
been successful. For all we can tell, he is now trying to
obtain a replacement for a failed device. Repeaters are
often subject to harsh environments, and recommending
less of a transformer than the OP appears to need would
be irresponsible.

But you don't know if he is using an inductor filter off the rectifier,
then it would be very conservatively acceptable. Also, the OP said
nothing about any failure, it was more that he wanted to build more of
the power supplies, wherein he is rewinding the secondaries: "I build
10-11 volt power supplies for my repeater's transmitters. Since they
pull around 20-25 amps I've been using 35 amp/12v rated transformers and
pulling a few windings off to get 10 volts AC. The vender (Hosfelt) ran
out of these and I'd like to get at least one more." Does that say
anything about failures? It sounds like he wants to build additional
power supplies.

[...snip drivel...]

There is little danger of the OP being misled by my post,
where my interpretation of his post was reasonably clear.
So I have to conclude that Fred is just adding noise for
his usual disgusting reasons.

It is important that the OP understand you are a crock of manure- all of
your posts are pure noise- you have nothing but irrelevant questions
about some elementary aspect of application that you never follow
through on.