first eliminate overload/shorting as a possible cause of hum. Then any of the following: wedges between core and bobbin hit the edge of the core with a hammer & cold chisel to jam the lams together put glue or tar on the lam edges
I haven't used it yet. I have a few cheap rubbish ACDC adaptors most or all of which make a noise. I broke one as described, but i'll try to experiment on the others too.
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it says it's an insulator.
I will reply to my post with links to pictures of the transformer.
Regardless there's a lot easier epoxies to use. JB Weld is very thick paste, you can get liquid epoxy resins which will be much easier to pour into something.
thanks for the tip, i'll be getting some. I posted some pictures of the transformer, I can't really get to it.. The copper coils of wire seem to be covered in some yellow thing and aroudn the whole thing there's this square housing with yellow tape over it.
But, just to get an idea of where i'd pour the stuff.. if I could. Here is a picture of another device I once had. The transformer was 'naked'.
It was a power supply card.
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you can click the image to enlarge it. Alternatively here it is
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There were a couple of transformers on it as you can see.
I think if the transformer is shaped like a doughnut. With my AC-DC adaptor, the wires go round in circles that are sort of parallel with the PCB. They go round the circumference of the doughnut. (at last I think that's what they do, i'd have to pull off the housing to get a better look)
Whereas on the power supply card that I linked to, the wires are sort of perpendicular to the PCB.
In the case of the power supply card, would I pour liquid epoxy in the middle. WHat is actually causing the hum? The coils hitting the doughnut(core?)
I just googled transformer coils core into google images. And got this amazing picture
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or for the archives
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I see the one in my AC-DC adaptor in that picture. It's second row from the back. And second , maybe third, from the left !!
Unless I'm mistaken the transformer you refer to is a fairly standard E core ferroxcube switch mode type. The cores are generally stuck together with epoxy or other suitable adhesive at manufacture. If the adhesive between the faces of the two E cores comes adrift you will hear a high pitched squeal and possible even a rattle. I would not try to fix this by covering it with any sort of gunk (or JB Weld). The transformer should be unsoldered from the board and the two E cores removed, their mating faces scraped clean and then re-glued under pressure.
Sometimes only one face may have come unglued so you have to heat the transformer core to a reasonably high temperature (I use a hot air gun) in order to soften the remaining bonds so you can get the cores apart.
Re-gluing with epoxy adhesive is good and will definitely fix your squealing transformer. I have also used Cyanoacrylate (superglue) to rebond core faces.
We used aluminum filled epoxy to make nearly bulletproof modules for a military contractor. The aluminum made it transfer heat well - but some of the modules would fail the high potential test as a result of the metal content.
An unfilled epoxy would be safer. or mix some non- conductive non flammable filler in like sand or chopped glass or ceramic micro balloons,
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James Sweet wrote in news:o8EFh.6020$RN6.3214 @trndny07:
Switchmode power supplies do not hum. (Where "hum" is defined as a 50 or
60 Hz, or 100 or 120 Hz sound.) They operate at much higher frequencies. Which is the whole point of a switchmode power supply: higher frequency means less iron.
Original poster: What did you hear from this power supply that got this whole thing started? Describe the sound.
putting aside the fact that it may be a capacitor humming. I may have other devices with transformers like that and they may hum. How and where would I put anything into that transformer? The transformer is surrounded in an outer casing. I tried soldering the transformer off (was a cheap acdc adaptor and that particular one I had was already blown). It didn't come off, so, I plied it off with a screwdriver, for the sake of getting a better look at it. Either way, whether it's on the board or off it, I can't see where i'd be putting the epoxy. The whole thing is surrounded in a square shell.
put the adapter in the refrigerator for an hour or two
find the seam that closes the outer halves.
lay the thing on a concrete surface, (it must be absolutely non-movable)
gingerly whack exactly on the seam, go rouund it a few times
most ultrasonically welded units will fracture at the seam, some chemically bonded will refuse to open, they require a jewelers hacksaw to splitt the case.
whenu get inside, dip the xformer in a good brand of varnish, then bake the thing for a couple hours at 250F in an oven
most buzzing is caused by poorly wound (looselywound) wires around the core that migrate as the unit experiences warm/cool cycles. some thinly applied manufacturing varnishes fail easily and then the insulating varnish on the actual coper wire wears and then you get a nice short that often will entertain u with a bang or flash or complete destructive fire of your home/business ;-))
all good reason to buy good adapters whenever u can
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