Ever wondered where our old unwanted AC adapters go to die, They go to China and like idiots we buy them back.
The Horror?
The Horror?
I bother to do this with transformer-type wall warts--the little switcher supplies are junk and probably best thrown away when they go bad.
If you find a linear wall wart (the kind with a heavy transformer) that has popped capacitors, they're usually popped for a reason. Unlike switching power supplies, linear power supplies drift upward in their voltage output over time, and can sometimes be alarmingly out of spec after just a year. These linear type wall warts will drift upward in voltage whether they're being used or not. If you've had one sitting around awhile, you should check it with a volt meter before plugging it into anything.
That being said, my favorites are the "desk wart" PSUs used for modems and such.
I've got some that I've had for over 25 years so that means they are original construction; even older than China:
http://www.vcfed.org/forum/showthread.php?21314-Unusual-but-usefull-power-supplies
Let me go and re-inventory them.I'm still using one to run an external floppy whose original application was for a Racal-Vadic VA3450 modem. That makes it pretty close to 35 years...
I check anyway, because you can never be certain that the polarity marking on the wart reflects reality. I've got a couple of them where what's measured on the end isn't what's shown on the case. But I've never run into what you describe.
Certainly, on simple rectifier-with-capacitor warts, no- or low-load voltage will rise to the peak AC voltage, but that's not due to any malfunction.
Caps usually go bad in those things because they get "cooked" by having no way to dissipate the transformer heat.
The output on a linear wall wart should never rise to mains voltage under any circumstance. This means there's a short between the primary and secondary windings and the unit has failed and should no longer be used.
If the voltage is higher, that's upwards voltage drift caused by shorted windings. If it's lower then it means that the wires coming out of the wall wart are too thin.
The output on a linear wall wart should never rise to mains voltage under any circumstance. This means there's a short between the primary and secondary windings and the unit has failed and should no longer be used.
This is really only a problem if the transformer is run at near or exceeded its amperage output, or if it's using Wofat brand caps.
I might be convinced if you could show me some real-world cases.