"Yellow" SMPS transformers

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If it started out yellow and then was turned brown from heat, I would expect it would not be a uniform brown color.

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If it started out yellow and then was turned brown from heat, I would expect it would not be a uniform brown color.

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Tried some yellow tape from a scrapper, presumably fairly generic for this purpose. Well its certainly not PVC as it does not melt or shrink at 205 degrees centigrade but it does go permanently faun brown from the original yellow. A mid shade colour to the example I have here. I will try again but to 220 degrees or so.

What I don't understand is that if this colour is due to heat then why exactly the same shade all around this SMPS transformer, so it looks like , an as-it-came colour. The surrounding core "frame" is also covered with this tape , not just the windings and its everywhere the same colour, top , bottom and sides and winding cover.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Hi!

The vast majority of the ones I have seen are yellow. I suppose this is the cheapest and therefore most popular color. Most people are probably never going to look or care all that much. :-)

That said, I have seen some red ones, purple ones and some orange ones. Something in the back of my mind wants me to say that I've seen dark brown ones as well, but I'm not sure if that's right.

William

N Cook wrote: :::[...]would a light brown colouring mean it was overcooked :::and shorted turns a possibility? ::: When I see orange-brown tape, I think

Yup. *Uniformity* is a big clue.

I wouldn't expect to see PVC (electrician's tape?) over transformer windings. The yellow tape I've seen is polyester: more stable than PVC but lower in thermal performance than Kapton.

If I understand the thread, you never saw the original color of the tape and think it has changed color to brown, possibly due to a failure. I'm wondering if Occam's Razor doesn't apply here (i.e. the original color WAS brown).

Rummaging around I've just found one with red tape, but dozens of yellow.

I think the small feedback coil at the very centre of this small transformer has shorted turns. The ps will work with light load if the attenuation in the feedbak path is reduced, but it all goes outside of operational window with high load.

Whether the tape was brown or yellow to start with.

Measuring inductance of few random low power such transformers with the main priomary and fb primary. One was 1.23mH and 6uH another

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

In message , N Cook writes

No. I've seen green, red and blue as well, I've also seen a Fawn brown colour and couldn't say if it was always that colour or not.

Does the shade change where the tape overlaps? I'd expect a slight variation, might also be some kind of conformal coating or insulating lacquer.

:ie the yellow PVC? wrapper often seen around the windings or frame, more so :than mains f transformers. : :Is it always yellow? :If light brown with other indications that there was an excessive load and :general overheating, would a light brown colouring mean it was overcooked :and shorted turns a possibility? An original one for this model not seen, so :no idea if it should be light brown or the ubiquitous yellow. : :I will try cooking some of the yellow tape stripped from a scrapper.

The Yellow tape is most likely 1 mil polyester film

eg. Permacel P256 or similar

If you care to search through the Permacel products gallery you will see that other there are other color adhesive tapes for the electrical and electronic industries

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I don't know what the 130 deg C refers to, but this tape and adhesive holds up well to short duration temp of 205 deg C , by 240 deg C it is puckering and losing conformity and adhesion - pretty impressive really for non ptfe tape.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on