Instructables
Picture of Pocket-Size Power Supply

I am a big fan of garage sales, flea markets, and thrift stores. They are great places to find used parts and materials for your next project. But one problem that I often run into is not being able to test battery powered electronics to see if they work. Because there are so many different combinations of batteries that are used in portable electronics, it isn't really practical to carry around batteries for testing. One device may need 6 AA's and another may require 4 D's. So I came up with this simple pocket-sized variable power supply. It can plug into either a 9V battery or a 12V battery pack. You can then adjust the output voltage to match the device that you want to test and attach the output wires to the end terminals on the device's battery connectors. This lets you power the device long enough to see if it works.
 
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Step 1: Materials

Picture of Materials
Materials
LM317 Adjustable Voltage Regulator
0.1 µF Capacitor
1 µF Capacitor
220 ohm Resistor
7 x 270 ohm Resistor (preferably 1/8 watt)
8-Position DIP Switch
Perf Board
9V Battery Connector
2 x Alligator Clip Wires

Note: All these parts are available at Radio Shack. I highly recommend using 1/8 watt resistor because they take up less space on the board which makes it easier to fit everything into a smaller space. Unfortunately I only had five 1/8 watt resistor so, I had to use two 1/4 watt resistors.
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EET62316 days ago
is there a more detailed picture of where everything was soldered together on the back?
DIY Hacks and How Tos (author)  EET62312 days ago

I have added a new picture of the soldering to step 3

davehartles699 months ago
Im currently working on a breadboard version would you like a pic when finished?
Did you ever happen to complete the breadboard setup?
Sure. If you want to post it in the comments, it might be helpful to other people.
saattvik2429 days ago
this project is from MAKE
Yes. I work for Make. My name is Jason Poel Smith. I create projects for them and post them to several sites for a wider exposure.
davehartles699 months ago
Do you have a picture of breadboard setup?
Sorry. This was one of the rare occasions when I skips prototyping and went straight to the finished circuit board.
agis6810 months ago
awsome!!! since the lm317 can handle up to 40V is suggested to use 12V A 23 mini battery? What changes have to do on above circuit


thanx
DIY Hacks and How Tos (author)  agis6810 months ago
You can use a 12V battery without making any changes to the circuit. You would just want to use a different battery connector.
Wo0kiE1 year ago
Brilliant!
I only have one Q?
How do you know how much current is being supplied across the circuit?
DIY Hacks and How Tos (author)  Wo0kiE1 year ago
The voltage regulator keeps the output voltage constant regardless of how much current is being drawn (up to its operating limits). If you really wanted to know the current, you would probably have to use a current meter at the output.
DragonDon1 year ago
This is a great idea!
wkoepp1 year ago
Even though the idea of this was to test electronics at say a yard sale, this design is excellent for breadboard projects if you don't have a heavy duty power supply or just don't want to pull it out. This is a nice little project I plan on doing soon. thanks.
atharva121 year ago
thanks
Please send me the schematic diagram... Thank you.
The circuit diagram is on step 2
Dr.Bill1 year ago
Good part of this is with a heat sink you can attach to a 12v source too. The lower the voltage it is set to the warmer the chip. I use this circuit without the resistors but I do use the potentiometer preset voltages for low power apps like AM/FM radio or a Digital Blood Pressure Monitor. These run my 6v powered speakers and provide voltages for experiments. Good choice for low powered devices. Mine are attached to a 200Ah battery.
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Orngrimm1 year ago
simple, but in some cases wastefull due to the linear-regulator.
a more efficient (But more complex!) solution would be a DC/DC-Converter with variable feedback-divider.
http://www.linear.com/product/LT1376 would be such a solution (Buck-Converter) with quite low parts-count. Simply adjust the voltage-divider from Vout to generate 2.42V to the FB-Pin and you have your variable Output up to 1.5 Amps with an efficiency of mostly over 80% and also often above 90%.

But as the efficiency isnt this an issue most of the time, your solution should fit the bill of many DIYers. :)
Actually dc to dc converters in this voltage range would be much less efficient due to the required operating overhead. The only time they are a valid source of power is if you are dealing with devices that require a tightly controlled and specific input. the LM series of voltage regulators are much more efficient. Your 80-90 % figures are not correct, as this output is at an unloaded state and drops tremendously as the operating load increases. The LM series regulator holds a constant 75-80% efficiency regardless of the load. I've had to redesign many supplies where DC-DC converters were grabbed off the shelf for critical use projects and replace the converters with LM series regulators, backed by FET pass transistors to save power for remote system use.
Excellent Instructable. I really like the idea that each dipswitch represents a single 1.53v battery, and also that you explain the voltage loss and facts such as (two 1/4watt resistors == one 1/2watt resistor) Question... I know "standard" voltage regulators follow the "lm70X" naming schema. Yes, I know a little off but it is something like that.... how do I identify variable voltage regulators thus allowing me to scrap them from old electronics, regardless of the fact that they are dirt cheap at Radioshack
Diy Hacks is correct. Solid state regulators are actually ICs so you only get family names IF anything is marked at all, that is an LM on the chip. Then the manufacturers proprietary markings. there are downloadable cross references from various sources, but they go out of date so fast it is unbelievable. your best bet is to go to the parts you are pulling and look for replacement parts through NTE and similar sources to identify them . It's a lot of work. but some times, worth it, mostly for the practice in desoldering more than anything,
I don't know of any universal naming convention. You will probably have to look them up individually.
thegrendel1 year ago
Elegant and useful. A very nice Instructable.

The only change I would suggest is choosing the divider resistors to set
more standard output voltages, such as 3.3 and 5.0v. The key is that these
resistors do not all have to be the same value.
the values in the circuit are fine, remember, batteries drop in output rapidly. AND standard resistors still 5% +/- tolerance. so in the end you would be literally measuring resistors to find the "perfect" values.
halamka1 year ago
I have a question. I bet that the x is a / in the equation. What are the output voltages? Something is wrong with the equation.
DIY Hacks and How Tos (author)  halamka1 year ago
The output are approximately 1.25, 2.80, 4.33, 5.86, 7.39, 8.92, 10.45, 11.98 with a max output of 1.5 below the supply voltage. I believe that the equation is correct. What are you uncertain about?
Excellent instructable. How about adding a small heat sink to the regulator? As it is I guess the max current you draw into the load is limited by temperature rise of the regulator before it shuts itself down is about 2W/(9-5)V = 1/2 A. The 9-5 is the 4 V difference between input and output. But with a small heat sink at least it might not burn your finger. ;)
adding a heat sink might be a good idea but you will never get the 2 watts you think . the LM series ( in this instance the LM317) are self limiting on current levels, the T series are all 1 amp max... this has nothing to do with temperature rise coefficents, it is simply a design parameter of the three terminal regulator. I've been utilizing the LM series regulators since 1975. They are wonderful devices, but if you want more current you need to add pass transistors, and these are where you will start to deal with the temperature coefficents limiting your current. The Regulator itself is actually more of a simple IC than a transistor as they can not be used as an amplifier.
PhilKE3FL1 year ago
Very nice idea, but as has been said, unless you're only powering very low power devices some heat sinking will be needed. Another thing that others may not know is that a 9V battery was designed for low power devices and can only handle something around 30 mA, that's 0.030Amp it most definitely will NOT be able to power something requiring 6V and 1000 - 2000mA (1 - 2A) the battery would die almost instantaneously even if the regulator could handle the power requirement of 6 - 12W. You'll stand a better chance testing out those baby swings with a nice 12 V battery, and some good heat sinking & probably a 3 - 5 Amp regulator if needed.

Today's electronics is using less and less power so perhaps a 9V "transistor" battery will work like this. (How many even remember that the original common name for that 9V battery was the "transistor" battery?) But some baby stuff requires, as you noted, C or D cells. If they require that size cell and multiple cells, 4 = 6V, 6 = 9V, & 8 = 12V then they require something on the order of 1 or more amps of current and a 9V Transistor battery maxes out around 30 mA that's 0.030 Amps, it might just work for some very small fraction of a second to power such a device. Take a 12V battery or power pack unless you know you're only going to be testing very low current devices.
this regulator, even with a substantial sink will only do up to 1 amp so the current sourcing of a 9volt is moot. This whole setup is geared around low current devices.
Ericc8151 year ago
This is a wonderful 'ible for some gadgets.
Now I ask - Would you consider a more substantial 'ible using a mini 12V sealed battery - a potentiometer instead of a switch & resistors - a 3 digit Vout readout???
This is what I would consider a true all purpose portable power supply which would be adjustable with heavy load capacity like some 1-2 amp hardware requires.
this regulator is only good for 1 amp with a decent heat sink
usbg3rd1 year ago
y not use a variable resistor instead of many resistors and switches ?
this gives you fixed voltages, a variable you would need a meter to read the voltage setting
DIY Hacks and How Tos (author)  usbg3rd1 year ago
A variable resistor would also work. I just wanted a setup where you could quickly dial in the output for various battery combinations.
rhooie1 year ago
Firstly I would like to admit I am an electronics illiterate. I have 2 solar panels at 12v and would like to set them up to be able to charge a cell phone or AA and AAA batteries. Could I use this to do so?
You Betcha! set your regulator to 5 volts (if this is what your cell phone calls for) and use the correct connector... also, add a blocking diode at the solar panels output, and feed it to either a rechargeable 12 volt battery or the largest capacitance that you can supply via ELECTROLYTIC capacitor(s) at the input of the regulator. You want about 1000uF minimum, wired like batteries on the input of the regulator (parallel or positive to positive negative to negative) so that you have what is called a constant current source.
gmh5760 rhooie1 year ago
Try using the search function at instructables.com or google. :) Seriously, quite a few how-to pages out there for solar chargers.
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