How to Convert an AC to DC Adapter to an AC to AC

Sometimes your wart adapters fail and you need a replacement. If it's no longer available from the manufacturer you may look for a universal one in a local electronics store, but they are almost all mains power to DC 'like a battery'. Here's how to convert one to AC at its output, as for some cordless phones. This requires the skill of being able to solder electronic circuit boards. If you are experienced then no problem, jump right in.


  1. 1
    Choose an adapter that supplies a voltage and current (Amps) in a range that is close to the failed adapter you are replacing. Your local electronic store may supply adapters that give ratings of ½ Amp (sometimes labeled 500mA) and 1 Amp. Cordless phone bases will most likely make use of the ½ Amp rating, devices that demand more current may be more suitably matched to a 1 or even 2½ Amp adapter.
    • The voltage from universal adapters is adjustable through a range most popular devices use. You may find a range like; 3, 4.5, 6, 7.5, 9 and 12 Volts. Don't be disappointed if you do not see an exact match, switch to one notch lower to select a safe voltage.
  2. 2
    Check that the replacement can be disassembled. The replacement you find in the store might be easy to disassemble check this in the store before you buy as ultrasonically bonded types are much more difficult to open and may need to be cut with a saw.
  3. 3
    Remove the rectifier and filter capacitors. Inside of these AC to DC adapters is a transformer, a rectifier and a filtering stage. The only stage you need is where the voltage is reduced from mains to a low voltage (the transformer) so remove the rectifier and filter capacitors.
  4. 4
    Identify the capacitors and the rectifier. The capacitors are typically 'can' type electrolytics and may be accompanied with ceramic discs for additional filtering.
    • The rectifier in most adapters is built using 4 power diodes to form a full wave bridge.
  5. 5
    Unsolder the capacitors. This will give more room to get to the diodes.
    • Before unsoldering the diodes, identify the end with a stripe and dot the board under with a permanent marker. This will help later on. Unsolder and remove each of the diodes.
  6. Removed parts
    Choose carefully which two diodes to bridge with insulated jumpers, One of the diodes splits the ‘live’ pole to the positive and ‘neutral’ to minus with the second of the only two board locations used for bridging.[[Image:
    • The jumpers can now be soldered in place, might want to try installing them on the trace side as the populated component side is more difficult to work with.
  7. 7
    Test. The primary purpose of the conversion can now be tested with a polarity checker or multimeter, to verify AC operation. Before the conversion, a polarity checker will light only when the red or plus is connected to positive of the adapter lead. Now it should light when connected in either direction. Multimeters will have shown a minus before the conversion when connected incorrectly.
    • After the adapter is reassembled, it is advisable to alter the label to affect the new changes. Where the product description reads AC-DC, the DC legend can be covered as the adapter no longer gives DC and the DC symbol can also be covered.
    • If labels are available in this size, they can be used to change the label to read AC – AC and replace the solid and dashed lines to an AC wave.


  • Beware burns. Those who are experimenters and are not used to soldering, soldering irons get hot and can cause burns and disfigurement.
  • Soldering releases toxic fumes that can cause harm to lungs due to lead poisoning. Use protective care and a fan to extract fumes away from persons.

Things You'll Need

  • Soldering iron (25W)
  • Solder .062" (cored with rosen flux for electronics)
  • Desoldering tool
  • Diagonal cutters
  • Wire strippers
  • Stand or clamps
  • 18 AWG insulated wire

Article Info

Categories: Electrical Circuits and Devices