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Wall Wart Scrounging

WallWartI killed a wall wart power transformer and decided to open it up. The plan was to find the failure and either fix it or gut it for parts. Read on if you have every wondered about the insides of a typical wall wart transformer.

WallWartGutsGuts:

The victim is a cheap Radio Shack 12VDC output Wall Wart. I used a pair of dikes to cut at the seam on each corner. The plastic cover popped of very easily reveling the guts pictured. The red and white wires at the top of the picture were cut from the metal contacts of the AC plug. The black wire pair leaving the picture on the lower left was the output lead.

The basic components are listed below

  • Transformer
    • Takes 120VAC and transforms it to around 12VAC
  • Bridge rectifier
    • The PCB with components attached to the transformer, light tan board with parts.
    • Converts the 12VAC into 12VDC
  • AC plug
    • Integrated into the plastic housing which was discarded
  • Output cord, 5 feet, with 2.5mm power jack

WallWartXFormerFailure:

The unit failed when I overloaded the output diving a bunch of high intensity LEDs. The AC input connection was an open when checked with an Ohm meter so I figured there was some kind of fuse inside the unit which could be easily replaced.

The primary winding was covered with several layers of tape but I could see a small plastic component was under the tape. I cut the tape and found a device labeled A2 AUPO which was open, problem found! I did a quick Google search to find a datasheet. The part is a thermal cutoff rated at 115 degrees C.

The A2 AUPO obviously failed as it should only be open if the temperature is above 115. The transformer never got that hot on the outside but I do remember the LEDs flashing on and off just before the wall wart failed but I thought it was a problem elsewhere in my project. Now I know that this part was getting hot, opening, then cooling off and closing to repeat the cycle.

I figured I could remove the part and build the guts into another project. Of course I would have to fuse the AC power input now that the protection was removed. Using the Ohm meter I checked the primary winding and found it open. Looking closely at the winding I could see that I cut some of the wires when I removed the tape. The transformer wire is very (VERY) small and easily broken. I estimate that this wire is about half the diameter of a human hair.

I might have been able to unwind some of the primary turns to remove the breaks but who knows how many turns that would be and the wire is so fragile that I would probably end up breaking it even more. I gave up on repair and went to scrounging mode.

WallWartBridgeScrounging

The most usable parts are the rectifier board and the output cable. The board is shown in the picture. The wire is about 5 feet long and has two 24 gauge conductors with a very common 2.5mm jack.

Even if I never need an AC to DC bridge the diodes and large capacitor could be useful.

I am sure the wire and the 2.5mm jack will be handy in the future.

For the sake of being through and because you might be interested I decided to recover the transformer wire as well.

WallWartXFormerTeardownGutting a Transformer

This transformer has a metal core made up of several E shaped plates. They are packed very tight and the center piece passes through the center of the transformer windings. This core would make it difficult to reuse the wire so we need to remove it.

Step one is to pull at least one of the core plates out. This will free up some space making it easier to get at the rest. Do not try to save the first plate.

The first place is that bent up piece of metal shown on the lower right. I bent and pulled it out with a pair of long nose pliers.

WallWartXFormerCoreThis picture shows what the plates look like. In this case they were easy to remove in tact. I had a large pile of these that were thrown away.

WallWartResultsThe Loot

Spool of transformer wire, full wave rectifier board, and a 5 foot wire pair.

Posted in Discovering, Scrounging.


9 Responses

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  1. NGinuity says

    Just a quick tip….

    You can use an O-Scope (provided you can find a friend with one), to diagnose the problem with your power supply quickly.

    Since a wall wart is mostly pretty much a sine wave to DC converter, looking at the wave form will quickly tell you the problem.

    Perhaps I will have to do a write up. Of course, those who own an O-Scope will probably already know how to troubleshoot something like that :-/

  2. drew says

    dfowler,

    Thanks for the tips. I’ll keep this in mind next time i need some coil wire

  3. Apnoe says

    That helps – good job,
    as many people do I have some broken transformers laying around here, too. Well, honestly I didn’t hear about a thermal cutoff IC or something similar. I couldn’t find the problem when I opened one of my damaged transformers few days ago – but now I have a guess what I could carefully look for 🙂

  4. Wes says

    That’s awesome. I’ve had to do something like this once. I just kind of jerry rigged it. Nice job!

  5. dfowler says

    Drew,

    Yes the plates are usually coated with a material that it intended to insulate them and stick them together. Fortunately this coating is not usually a very good glue. It’s often brittle and you can separate the plates with some effort. I uses a pair of long nose pliers and an exacto knife to get them off. The first plate was the most difficult as the core is usually very tight with the windings. Once the first plate is out, there is room to work and it gets easier as more plates come out. The first one is a real pain.

  6. dfowler says

    Meico,

    Yes, magnet wire and transformer wire are two names for enamel coated solid copper wire. The primary winding (120VAC Side) on these wall wart supplies is usually very small wire, almost invisible. The secondary winding usually had larger gauge wire.

  7. drew says

    How did you remove the metal plates from the core windings? Whenever I’ve taken an adapter apart, the plates were always glued together or somehow otherwise attached in such a way that they don’t come apart.

  8. AuroraAlpha says

    This is a great (and helpful article) I always wanted to get a better idea of the electronics inside these things so I could find out how suitable they would be for running lasers and other sensitive electronics off them. I am somewhat surprised just how simple these things are.

  9. Meico Tenkawa says

    Is transformer wire the same as magnet wire? If so, this would be a not half bad source for it. ( I have a couple dozen wall warts just laying around the house, oh the joys of being a pack rat )

    Meico Tenkawa