Laptop A/C adapter

[bbmonster]

I just scavenged a laptop AC adapter. It's rated at 18V 3.1A. No project in mind right now but how would I go about using it to power something someday? Is it just plug and play for 18volts? Or would i need to run it through a voltage regulator or something before it's useful? Assuming I'm using it to power something from 12v to 18v.

[anchovie]

Stick a multimeter on it and see if it really is 18v.

[JKowalski]

For a laptop power supply, I would assume that it is well regulated already. It should be plug-and-play. Make sure your circuit is okay with 18V.

[WLS]

The adapter may produce ripple and the circuit you use it on may require additional filterring.


Bill

[earthtonesaudio]

Yay for salvage!  Make sure the polarity is right for whatever you plug into.  Most non-stompbox adapters are center positive.
It's probably pretty good in terms of regulation, ripple, and such.

[waltk]

Nice find... With this you could power a decent practice amp, or a whole pile of stompboxes.  Lots of circuits you find here can use the extra voltage for extra headroom, but if you want to reduce the voltage, I recommend a LM317 (adjustable voltage regulator).  I use these all the time with a simple circuit that you can find on the data sheet.  If you use a trimpot for one of the resistors that controls the output voltage, you've got a lot of flexibility.  It gives you output ranging from 1.2 volts to 37 volts, but would be limited to the input voltage of your laptop adapter minus 1.5 volts.  The LM317 is guaranteed to supply 1.5 amps.  It will often give more than that (with a good heatsink), but probably not the full 3.1A your laptop adapter is rated for.  If you want to get the full rated output of your laptop adapter, you could use an LM338 - same as the LM317, but rated for 5A.

[bbmonster]

Thank you for your replies, guess I got something good in my hands. Gotta love the free section in Craigslist.