35amp tranformer wanted

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:

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

Welcome.

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

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.

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

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

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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

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Googling for 430-7001 gets a hit at:

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

Which looks like exactly what you want.

--
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.

[Derf transform applied.]

"Fred Bloggs" wrote >>

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.

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.

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 ?

*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

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 ?

*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

["Bloggs" had asked the following:]

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.

of 40oC- maybe his environment makes the 35A

on the worst case RMS/DC when the load draws 20A DC

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.

i.e. ignoring given information.

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.

build more of the power supplies, wherein he is

repeater's transmitters. Since they pull around 20-25 amps

these and I'd like to get at least one more." Does

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.

....

posts are pure noise- you have nothing but

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.

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

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

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.

i.e. ignoring given information.

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...]

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.e. ignoring given information.

Puzzling.

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

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

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.

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".

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.

Your speculation about my motive is incorrect.

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

i.e. ignoring given information.

--
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.

microwave oven

NT

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I agree. :-)

Me Too!

;-)

like you could be certain of the meaning.

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

of 40oC- maybe his environment makes the 35A

on the worst case RMS/DC when the load draws 20A DC

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

[...snip more drivel...]

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

I read in sci.electronics.design that John Fields wrote (in ) about '35amp tranformer wanted', on Sun, 1 May 2005:

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