Instructables
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.
 
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Step 1: AC and DC power

Picture of 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.
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PhilKE3FL8 months ago
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!
PhilKE3FL8 months ago
"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: http://cs.yrex.com/ke3fl
LasVegas7 years ago
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 :)
pir8p3t3 (author)  LasVegas7 years ago
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.
PhilKE3FL8 months ago
"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 http://cs.yrex.com/ke3fl - 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.
ocelot16336 years ago
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
Power plants never generate DC power. That's impossible. The difference was, a long time ago, AC power was created and immediately turned into DC.
There are two ways to generate power:
AC alternator
DC motor

Most modern power plants use an alternator that makes AC
AC is a better choice because transformers only work with AC.
AC is also better because converting AC to DC only needs a diode.
DC to AC needs complex circuitry.
i've got to respectfully disagree. consult your history books and get back to me. you might want to read about the "war of the currents"
No. I know about the "war of the currents". The problem there was not how they generate it, but how to transmit the power. Any power plant that uses a turbine, such as a coal, gasoline, nuclear, hydroelectric, wind, generates AC current. It is impossible for them to generate DC. Look at what thermoelectric said right below this. "They generate AC with a frequency equivalent to the input speed of the generators." That is exactly how it works. Consult your science books and get back to me.
Edison's original distribution system was all DC... from generation to utilization. because of the inefficiency of DC transmission, customers had to be within about a mile and a half of a generating station. it wasn't until after 1896, when westinghouse installed a hydroelectric polyphase AC generating system at niagra falls, that AC generation and distribution began to widely replace DC systems.
Can someone help me explain here? There are very few ways to generate DC current, and none of those ways existed back then. Examples of this are photovoltaic cells or chemical processes like batteries.
"a long time ago, AC power was created and immediately turned into DC"
ok, i do see what you're getting at here...but this process is happening within the generator, through the use of the commutator. the armature windings rotating through the magnetic field of the stator do produce an alternating current, but since the experimenters in those days didn't really know what to do with AC, they employed a commutator to periodically reverse the connections between the armature and the external circuit. thus, the dynamo generator generated DC current.
for an example of an electromagnetic generator that produces DC without the use of a commutator, check out Faraday's Disk
I have to agree with jhvh here. Edison's system ultimately produced DC current. The issue was that you either had to be very close to the power plant to get power, or have quite a few power stations to maintain the current in the power lines. Plus, they had to be HUGE to carry enough DC current for public use. Tesla's AC used much thinner lines relative to Edison's DC and stations could be spaced much farther apart, giving more people easy access to the power even when they were far from the plant. Now, I'm not sure how Edison generated his electricity, I just know that once it left the plant it was DC but that AC proved more efficient and triumphed over DC. Sorry if I rambled :P
The car I had in the 1960's had a dynamo this was an ac generator with a commutator and brushes to convert it to D.C These days cars use an alternator. It has built in diodes so it dishes out D.C.

The power plants don't generate DC power, They generate AC with a frequency equivalent to the input speed of the generators, They probably have a control on the generators to stabilize the speed to keep the frequency steady. Well something like that but they DEFIANTLY generate Alternating Current.
Edit: Good Instructable tho . Found it very useful
i did this when i was 5 years old!!!!!
w0rm55 years ago
Power PLANTS DO produce DC power till it get to a central near you home. Always this way, and like my man I also did this long ago, but good project, i use it to keep a stable voltage when charging BMW batteries, since their actual systems, navigation, start, and other stuff, can be damaged if power goes under 13V while charging the batteries.
johnny3h w0rm54 years ago
Many, many of the following comments, as well as this one are in ERROR.

Power plants do create Alternating Current [AC], even though they could build "DC generators" as Thomas Edison first did.

The reason they make AC rather than DC is that DC is very inefficient to transfer [transmit] on wires, especially for distances greater than a mile or two.

AC is orders of magnitude more efficient to transmit on long distance high voltage power lines [often called "Hi-lines"].  The electricity/power is also easier to control by changing the voltage, and thus power, using transformers which do NOT work on DC.

This comment should apply to ALL of the following comments that erroneously transpose the terms AC [Alternating Current] and DC [Direct Current].
it is actually DC till it gets to a substation because ur wrong on the DC is less efficent part is actually more efittent than AC simply baceuse it is direct. true that that power plant generates ac but it rectifys it into dc to carry over long distances then it goes to a substation where the dc is passed throught a step down transformer to feel ac current in to our homes it needs to be step down to 220v (canada or us) beause without this our mains supply would be 1000V 3 phase power. so johnny3h i think your comment is the error sorry. but i hope this clears things up for ppl :)
Coilsinamotor obviously has no idea what he is talking about. Same thing goes for w0rm5.

Johnny3h is 100% correct.

Source: I am an electrical engineer.
Wrong! See my new comment above. It's relatively new, but it's already happening. You may be indeed be an engineer, but if so, you're not keeping up.
w0rm5's comment on DC may not be in error. His English usage signals that it is not his first language. In the U.S.A. we are currently looking at high voltage DC transmission that gets converted locally to 120V AC as on of our much touted smart grid options. AC is only efficient because it is easily and simply transformed from high voltage long distance lines to 120V local AC. Just need transformers, nothing else.

However, there are substantial radiation losses over long distances with AC. Who hasn't heard of the farmers who put up a power cable in parallel with a high voltage transmission line to power a home, etc. free of charge? In some parts of the world, as we're contemplating here, with modern technology we can transmit very high voltage DC (HVDC) and then convert to 120V AC locally. w0rm5 may live where this is already being done. My bet is Germany, where there are several such projects. Follow the link below:

http://en.wikipedia.org/wiki/List_of_HVDC_projects
76543213 years ago
Just curious, why is having less current going to make a "pyrotechnic time bomb"?
You're thinking the wrong way around. What the author wrote (three years ago, by the way :-), is that if your device draws 1A, but you try to use a 600 mA supply you're going to have problems. In particular, the supply will overheat, maybe melt, and quite likely short out while it's plugged in. The end result, if you're not paying attention and yank it out of the wall, will be an electrical fire inside the walls of your house.
Plasmana5 years ago
Just so you know what is VAC, the manufacture actually mean V (volt) AC (alternating current), so it is an AC adapter.
Korey6 years ago
Im trying to power a label maker without batteries and i dont have a wallwart to fit the specs. It requires 7V 1.2A...Would i be able to just plug it into 7V out of my DC power supply?
ReCreate Korey5 years ago
anything from 6.5 to about 7.5 volts will be safe for your thingy though the amperage(which is 1.2a)should be at least 1.2amps and should not go to far above like 10 amps as for batteries you should not charge them with a higher amperage than what they are
Ranie-K5 years ago
I also use a generic transformer (2,5A 5V) for my Creative Zen Vision:M -works just as fine as the original and way faster than charging through my laptop's USB.
hondagofast6 years ago
You can use a PSP charger to run a Sony Walkman, but that's limited to people that have PSP's.
really?good job sony!
Derin Derin6 years ago
oops,their u-nav lcd cracks easily,my friend had one which we took apart
it took me HOURS to make him not drill thru the lcd
Kyri7 years ago
Good job, I'd been wondering how safe doing something like this would be...
stereo1237 years ago
i want to learn eletronics to make stuff that goes bleep and blink lights, but i'm having a hard time finding guides that don't delve into deep theory without explaining what are they useful for. I like your article. Just one question, why should i use an adapter with a higher current value if i don't have an exact match? I'll believe you and not try and underrated one, but why??
mathimaticaly, V=IR, the R (resistance) of a divice is fixed and the V(voltage) of these power supplys has a maximum value but can be lower. the wall current can supply a huge amount of current (15+ amps usualy, most wallwarts use something like 1/2 to 1/4 of an amp). the resistance of the device and the max voltage control the amount of current used. if the current is to low, the equation still has to balance, so voltage drops. many electronics require a minimum voltage to work (most chips need 5 v) or they won't work.

another way to think about it is how well does a flashlight work with AAA batteries vers. D batteries. the source voltage is the same (with the same number of batteries) but the avalible current is much greater with the D cells. motors are the same. HOWEVER, without a limiting resistor, flashlight bulbs and motors will try to draw all current avalible (they have very low resistance). the current in that small amount of resistance creates heat, and enough heat burns out the wire or spins the motor so fast that it falls apart.
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