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.

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.)

"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.

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 ?

Btw - it's common practice to return to the newsgroup to read the replies

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 ?

Btw - it's common practice to return to the newsgroup to read the replies

Graham

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.

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

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

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.

i.e. ignoring given information.

microwave oven

NT

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....

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.