Wall Wart question.....

I have an NCE cx12v500 direct plug in class 2 transformer in the form of a wall wart. I accepts the USA standard of 120 vAC in, at 60 Hz, and outputs 12 vdc @ 0.5 A.

I thought this was the recharging unit for my portable drill, and so I plugged it in. After a few hours of charging, the drill moved but was sluggish. I unplugged it, and when I tested the output, it had dropped to around 1 - 1.3 vdc.

I can't seem to find a way into the unit either (molded plastic) without sledge hammer or hacksaw usage coming to mind.

Did I fry this one I think I did, but I am looking for a possible, no and solution from someone :-)

Aaaargh ! I took it apart finally sawed a notch in it and pried it open... and there was #1: NO regulator *sigh*, and #2: NO fuse of ANY kind, and #3: just a tiny board with a 1,000 uF cap on it and 4 diodes (bridge configuration).....one by one I took components off and tested them with my VOMM and sure enough, all the components were good.
Then I tested the transformer......and both sides should have tested closed or short, but one side (output) tested OPEN. *sigh* It fried the transformer ! :-(

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110100101109 years ago
some of them have protection they call 'thermal fuse'. this is not fuse at all but thermistor connected in series with the primary side of the transformer. if you see some electronic component under the tape that covers the transformer windings thats it i once had a transformer with a break in the thermistor (it came from control board of microwave - a small 3 V 150 mA transformer). i shorted it (connected the transformer without protection) and it worked. i added a simple 100mA fuse and put the transformer in a metal box so it is not fire risk if it overheats or something. the transformer still works as battery charger i sometimes use also disconnect the board with diodes and try to measure AC directly on the transformer outputs
Goodhart (author)  110100101109 years ago
after tearing back the tape and paper, I didn't find anything but very smelly wires (as if the insulation had gotten too hot).
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then its dead you can drill and hammer the fried windings out and wind it with new wire (thicker and shorter one). it is good for some of the 'ibles here / as bass booster for speakers / some more stuff
Goodhart (author)  110100101109 years ago
Hmm, yeah, it would have to be shorter, as I don't have the patience to thread the needle 5,000 times :-)
winding few conductors in parallel and connecting the ends makes work easier in large transformers you can use IDE cable (from computer hard drive). one turn of it is equal to 40 turns of one wire. connect the ends in 1 pin mismatch to get 2 long coils with ends. you can then connect them in series
Goodhart (author)  110100101109 years ago
Thanks, sounds like a plan :-)
Big Bwana9 years ago
Sounds like you fried it.. You can open them by giving them a good whacking all the way around the joint, I do it with the plastic end of a heavy screw driver and this breaks the glue holding it together, don't whack it to hard, more whacks is better then real heavy hard whacks.. Once you have it opened there is a thermal fuse under the tape on the 120Vac input side of the transformer and that is where most wal-wart problems are, now if you defeat this protection it may allow the transformer to get hot enough to catch fire, so keep an eye on it when your using it, or replace it with another thermal fuse which in some cases costs more then replacing the whole walwart with a new one .... And once your done fixing it just glue it back together with model glue / super glue / or tape if you feel like you may have to open it again....
Goodhart (author)  Big Bwana9 years ago
Because it's lack of a thermal fuse, the Xformer failed

I notched the plastic case with a hack saw....then pried it open.....what I found above edited was not good.
If it has any safety ratings on it there is a thermal fuse some where, however I have seen a few where the fuse is in the middle of the windings and this is not practical to fix, and yes I've seen a few where the windings burn to .. And any small transformer is not really worth the effort to fix it.. And did you find one, or would you like me to mail you one (( I just found a 12 VDC 1.5 amp small and very light switched mode supply 110 to 240 VAC input at the e-waste re cycler )) your welcome to it if you want it..
Goodhart (author)  Big Bwana9 years ago
I will have to give that a go tomorrow when I am home. It doesn't appear to be glued though, it looks like the case was melted together, but I will see for sure. I have a few thermal fuses lying about so, if the values are near enough, that may be the ticket if I can get it to crack open ;-)
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