Tingles from power supply

How much capacitance would you expect from say a 25VA transformer ?

Graham

Err...read what is inside the parenthesis....

I'm

company and

online

sadly

Something like that. It'll do wonders for your income too.

Graham

and

online

Moral: if you cannot do the work, get an MBA?

In fact many, if not most new manufacturer supplied plug packs are switchers these days. The cost is now similar, with the bonus of less weight, and usually universal supply voltage.

MrT.

Inter-winding capacitance varies from one transformer to another based on the transformer construction and the winding placement, and the number of tape layers (or paper) between the two windings.

It varies with the type of transformer, and how the windings get laid onto it, and the level of separation between them.

Same rules for ANY capacitor, donkey. Two "plates", which make two area sizes, and one gap between them consisting of either polymers or paper, or impregnated paper. A layer of windings looks like a cylindrical plate. Basic cap formula, physically speaking.

This one reason why most transformers do NOT directly 'nest' the two windings together. Good magnetic coupling, but too much inter-winding capacitance.

Seperate them with transformer tape or paper, and the cap value drops with near no loss in coupling. Also, an isolation benefit is gained.

And yes, you already knew this, you just are losing brain cells at too high a rate.

All but the big name boys buy from an OEM supplier, and even some of the big guys do as well.

The small wall hung jobs only are switchers if the power need calls for it. If it a simple trickle charger or other such low draw device, you will still find the old style in use. Also true if ripple figure does not pose a problem, like in cases where the regulation circuitry is in the device. It is cheaper, and Chinese makers ship by the container full, with weight only adding to cost when it is overtly different. There are even AC 'feeders' for this purpose. Particularly since OEMers still have tens of thousands of them on hand.

As you know, end of year inventories do not have the same consequence over there as it does here, so an order for 100k of something might cause an mfg run of 140k pieces. So there is surely a huge glut of the old style devices still available. Also, transformers themselves are still very cheap, and get made in even bigger quantities on practically unattended machines.

The transformers I've seen that are intended to provide isolation have windings that are completely separate, such as this

where the top winding is the secondary, and the bottom winding is the primary. The intent clearly being that there is no way that the two windings will become electrically connected.

I would not expect there to be much inter-winding capacitance.

Sylvia.

Seperation with fish paper (transformer paper)of a couple thousandths of an inch, plus the mag wire insulation, plus impregnation, if any is quite good enough, and can be a mere few thousandths total, and provide 6kV isolation. Transformer tape is also only a couple mils or so, and most of these super small jobs are usually incorporating cheap elements like paper and there usually is not large gap.

Most are NOT made in the style you gave a link to. Most are one winding right on top of the other, and it makes no difference which one is inside, and which is outside. That has more to do with construction ease. That 'ease' changes as the turns ratio grows. It is far easier to wind a couple thousand turns of an HV transformer right on the bobbin base to achieve nice, flat winding layers, and then add the primary onto that. Placing the larger wire size primary first makes for a very 'terrain' like winding layer on the small gauge secondary.

These relatively low ratio devices though, can be found to have been wound either way. It is all a matter of maker preference as there is typically no huge efficiency difference between the choices.If there is, the most efficient method will always be utilized. With these step down jobs, you will find most to be primary first.

Leave it to a total retard like you to be so stupid as to think that such a number is possible. You're an idiot.

Don't be so full of yourself, s*****ad.

I'm

and

online

Those that can, do. Those that can't, teach. Those that can't teach get a PhD... to wit, Slowman ;-)

...Jim Thompson

I see no tranformers there.

Graham

Must be one of them new fangled websites with expiring URLS.

Put M6672 into the search box.

Sylvia.

Ah those. Yes, very common at lower powers.

Graham

It was there before, and it was a TRANSFORMER, not a tranformer.

Is the Donkey a T-girl? Bwuahahahah!

Must be a new way to SPAM folks.

switchers

Which has nothing to do with transformer Vs switching supply choice though. The OEM's make both.

Maybe, but since trickle chargers are far less comon now, that is a shrinking market. Your undefined claim of "most are not switchers" and "few are" is what I dispute. It is certainly not my experience with new products.

MrT.

That was not the point. The point was that the bigger makers actually spend more thought, time, and resources to make supplies that will last longer and provide 'cleaner' power rail(s). Those makers make their own designs.

Of course OEMs make both.

The easiest way to tell is by weight.

Can you tell if a handgun is loaded or not by the feel in your hand? If so, you should have enough brains to make a valid declaration about what is inside a plastic box that you hang on your outlet... by feel as well.

I certainly can.