Need a very cheap power supply or wall wart but can't find the right voltage?

Picture of Need a very cheap power supply or wall wart but can't find the right voltage?
Ever had a need for a replacement or project power supply that you just can't find anywhere or costs way to much?
This instructable will teach you to take junk wall warts from thrift stores and hack the circuit to give you what you need. Not the connector but the power itself. I never pay more than a buck for one using this mod.
I have been doing electronics experimentation for decades and often find a major stumbling block for my small projects a suitable power supply. 
We can very simply change a single part and "make" what we need.

Need 5 volts? 9 volts? 12.6? 13.5 or any number in between? Here is your answer.
Should cost about 1 dollar!

Here we go.

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Step 1:

Picture of
First a tiny background.
These little wall warts come in 2 styles. Switching and Linear.
We need to use switching type for this hack. 
How do I tell the difference?
Linear supplies, which we don't want are usually heavy in the hand and rated input is 110 - 120 VAC 60 HZ
Switching are rated 100-240 VAC 50-60 Hz, thats what we want.
Cool. I'm going to look at this again later. I want to use a power adapter from a dead printer (16v DC output, wall wart for USA) to power a "12v" picnic cooler in the house, before loading it in the car for trips. I also would like to power a CB radio in the house sometimes. I could buy an adapter for that at $30. But I already have this printer power cord. I like the note about potentiometers. There are very common ones for guitars at 250,000 and 500,000 ohms, "linear taper" and "audio taper". I'm new to this, but would the "linear taper" work better? They're $2-4 at Radioshack or free on busted guitars.
My plug says input 100-240v /1A 50-60Hz. Output 40W max, and there are 2 "hot" wires, 32v DC 940mA LPS (what's LPS) and 16v DC 625ma. The cooler is a generic Walmart Igloo cooler with the peltier junction type cooling system and no switch, just a cig. lighter plug. What do you think? Can I just wire a cig. outlet in a box to the 16v and plug in the appliances (cb or cooler)?
lkndave (author)  Yard Sale Dale2 years ago
cig adapter to peltier will work fine. if your trying to use your 2 output adapter in your car it wont work it needs 100-240 VAC to work. cars are 12.6 to 14.5 DC. the adapter will just burn and cause a small fire.
No, I am intending to cap off the 32v wire, and use the 16v wire ending in a cigarette outlet from autozone, to use household power for 12v cooler in the house, overnight before the trip or as an office fridge. then I can just plug the fridge in the car as normal and it will already be cold.
lkndave (author)  Yard Sale Dale2 years ago
remember the power going to the fridge (peltier) is going to have to be from 5 to 10 amps. i would guess you printer supply is not anywhere near that. i think it will be weak to work.
everyone i know that used these for their car has gotten rid of them because it will kill your car battery in a few hours.
just sayin'
I like using them in the car. I usually use them bring home gourmet groceries from a distant city, or to carry picnic food 1 way to events. I have a large truck battery, but don't leave the fridge on without the car running for more than 1 hour. I used to use one in a diesel truck, with a deep cycle battery under the bunk. The fridge battery had a cigarette plug going to the truck system, and was interrupted by a voltage controlled shut off that cut the connection between the truck and fridge battery at 11.5 v, but the truck had its own shutoff at something higher. like 13.5, which cut all power use unless the truck was started again. I'll just buy a converter from Amazon. I got one for $20 last year that is made for the 12v coolers.
If you are charging batteries with the wall wart, how do you control it? Do you just use a cheap multimeter in the system and unplug it when it's "done" (unplug wall wart to check, right)?
lkndave (author)  Yard Sale Dale2 years ago
if you are using a fixed voltage wallwart to charge batteries the power must be controlled to avoid overcharging. discover circuits . com has plenty of simple circuits. if you over charge a litium battery they will explode. Nicads and NiMh's will stop holding a charge after a few cycles. it ruins batteries to keep them on charge all the time.
lkndave (author) 2 years ago
linear pot is the way to go for controlling anything that is not sound or audio related. Peltier junction coolers and CB radios take a bit of current. peltiers should have 5 amps available and should be at least 3 amps. make sure your wall wart can handle it.
lkndave (author)  lkndave2 years ago
PS the peltier is OK with 16 V the CB should be 14.5 volts.
Thanks for the tips.
AptPupil2 years ago
Very cool. Good, clear instructions. Very useful!! Thanks
qwerty1562 years ago
Thanks a lot, very useful trick indeed :)
cool project, great explanation! I might try this sometime