Reuse "Wallwart" Transformers





Introduction: Reuse "Wallwart" Transformers

Lost that special plug for your favorite appliance or toy?

Want to utilize that "DC power" jack on your walkman, but it didn't come with a plug?

Need a power supply for that special project but not sure which one to use?

Here's my little guide for picking the best power supply for your needs.

Step 1: AC and DC Power

AC and DC power are the two types of power which you are probably familiar with.

AC power comes from the power company, and is accessible through the outlets in your house.

DC power comes from batteries.

Sometimes we need to convert the AC power from the wall to DC power in order to run a device which normally might run on batteries. The tool for this job is an AC/DC adapter or transformer which is often referred to as a "wallwart" as it sticks out of the wall in an unsightly manner.

Most appliances that require an adapter like this have a label near the power jack which details about the voltage and polarity required.

Step 2: Understanding Electricity Basics

Electricity is obeys some pretty simple rules. Understanding these rules will help you to use electricity safely and effectively.

To help explain electricity I will use a metaphor which is mostly analogous to the behavior of electricity. That Metophor is the behavior of water in a system of pipes and tanks. Electricity is made of charges, free electrons, which in most metals are able to jump from one atom to another with little problem. In our metaphor we will consider the volume of water to be as a quantity of charge, trading liters for coulombs as it were.

Electrical Resistance is analogous to water flowing in a hose. If you turn the water on a little bit, the water begins to flow out of the hose at some slow rate, maybe 500mL/sec. If you put a kink in the hose, the water begins to flow more slowly maybe 100mL/sec. The pressure at the source, spigot, remains the same, but the rate is decreased as the resistance increases.

Electrically we call the rate of flowing charges Current, and we measure it in Amps which are defined as Coulombs/Second.

We call pressure Voltage, and measure it in Volts.

Resistance is called the same and measured in Ohms.

Just as with water, if we increase the resistance in a circuit and leave everything else the same, the current will decrease.

Now back to the hose. If we let go of the hose so it is flowing at 500mL, and then turn up the spigot to full blast, the rate of flow will increase, maybe to 1L/sec.

In this case electricity also behaves similarly. As the voltage is increased, if resistance stays the same, current increases.

This is why the most important thing to note about your wall wart will be voltage. IF THE VOLTAGE RATING DOESN'T MATCH EXACTLY, THE ADAPTER IS NOT SUITABLE FOR THE JOB. The result will be either the device not powering on for lack of power or the device frying in spectacular ways as large amounts of current it was never designed for burn away its delicate circuitry.

Step 3: Understanding Electricity Basics Part 2

The water metaphore runs kind of thin here so we have to discard it for now to discuss Amperage (current) ratings.

Your wall wart will have an amperage rating, and your device should have a current requirement as well. If they don't you can try a fairly strong one and check it repeatedly for heat build up, but I strongly suggest finding out what the actual requirement is from the manufacturers specs or the manual if it's not printed right on the device itself.

Lets say your device says that it need 4.5V 1A DC. If you plug a 4.5V 600mA power adapter into the device, it may work. BUT DON'T BE FOOLED! You have created a pyrotechnic time bomb waiting for it's chance to melt open and burn your house and family and all you hold dear!


The point is have the # of mA higher or at least equal to the devices needs.



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    pir8p3t3 - Thanks it was very good and safe. I've posted a few other comments and a link to my website and article about the older linear wallwarts and how to determine when it is safe to use a wallwart that doesn't match the device's requirements perfectly. My article was for Linear wallwarts only, switchers are more limited in what they will supply. However, there was another Instructable showing how to use a switcher, (it would work with a linear as well) and then a linear regulator LM78XX to get the voltage needed. Then as long as the switcher can supply more current than the device needed you'd be all set. This was almost identical to another article of mine published in QST magazine years ago for doing something very similar. It's good to see these things here!

    "NEVER NEVER NEVER NEVER USE AN UNDER RATED ADAPTER!" - This is true for the newer switching regulator wallwarts. On the other hand switching regulators will not supply more current than they are capable of & so the device simply won't work, at least that's been my experience with switchers. As for linear wallwarts my article covers how and when it is OK to use a wall wart with different ratings that the device needs. The article is: "Reusing a Wall Wart, Revisited" - my website is:

    Yes. We call pressure, Voltage, but it's normally represented in the equation as 'E' (for energy). So the equations would be shown as E=IR and P=IE.

    E stands for Electromotive force, that's your pressure. I'm old school & I still use V = IR, but I know better :)

    I'm sure a quick perusal of some textbooks on the subject will offer up a large number of exaples where the preferred notation for electrical potential is V. The notation is a matter of preference, and I have seen all three used by different professors.

    "IF THE VOLTAGE RATING DOESN'T MATCH EXACTLY, THE ADAPTER IS NOT SUITABLE FOR THE JOB." - Not completely true I wrote an article on how to select a linear (transformer) wallwart. The original was published in WorldRadio the second rewrite that used a program that another ham, George Murphy, VE3ERP, & I collaborated on is up on my web site it is - search on "Reusing a Wall Wart, Revisited" to find the link to the updated article. NOTE: The program was written in BASIC for DOS computers and probably will no longer work on Windows 7 or newer Windows OSs. I should probably convert it to JavaScript, all I need is time.

    Ummm buddy, I dun mean to be rude or anything but to correct your statement "AC and DC power are the two types of power which you are probably familiar with. AC power comes from the power company, and is accessible through the outlets in your house. DC power comes from batteries." Truth is, that Power plants generate DC power, and it is run as DC until it reaches a transformer, witch converts to AC, but still the DC currents are EXTREMELY high.... regardles, proceede w/ caution

    power plants generate power via different kinds of induction based electromechanical converters, and none of them output DC. DC is generated with chemical or photovoltaic processes, none of them very popular so far. Electricity is generated in AC, voltage is elevated to several hundred thousand volts with transformers and then transmitted using transmission lines typically staying in AC (with some very rare exceptions of high capacity voltage DC lines). The transformers outside your home are always DC and always take the voltage from several thousand volts AC to the 110 or 220v you use in your household. Tesla won this fight to Edison, early last century, and we haven't bested their discoveries yet.

    Transformers don't convert AC to DC or DC to AC. They simply step the voltage that delivers the current and the resulting power either up or down. The power is almost the same out as in, since transformers are very efficient, so high voltage means low current for roughly the same power and vice versa. Power equals voltage times current and you don't get power from nothing, so they have to multiply together to give almost as much power out as in.

    power plants did typically generate DC power...before CE 1900, that is... there is still some limited use of high voltage DC transmission today. mostly because of its ability to transmit large amounts of power over long distances with lower losses than with AC