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Picture of Easy variable voltage power supply
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Sometimes, to supply the necessary voltage in a project, i needed to buy a lot of batteries, or i had to look for a proper power supply for hours and it is not necesary, beacause now i have that awsome variable voltage power supply that can supply from 1,25 to 29 volts and 500mA, but if you decide to make your own, it would be able to deliver 3A.

It is easy to make and only cost me 4$.
 
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Step 1: Materials

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-A 30-32v power adapter. (Mine is salvaged from an old printer)
-A DC-DC buck converter. (1$ on ebay)
-A LED panel voltmeter. (2$ on ebay)
-An audio spring terminal. (0.40$)
-A potentometer, the same value as the one of the converter, mine is 10K (0.60$)

Step 2: No project box needed

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I know that kind of power adapters have a lot of empty space inside that we can use to place our components, so i'll open it to se if it can be the project casing.
If you use a transformer with a rectifier circuit, you'll need a different box.
As you can see un the pics, there's enough space for all the components.

Step 3: Electrical connections

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The wiring is pretty easy, you can see it in the diagram.
What you'll need to do first, is replace the small multi-turn potentiometer with the big one, it'll make the voltage controlling easier.
Then connect the voltmeter and the spring terminal in parallel at the converter output.

Step 4: Preparing the case

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Open three holes in the case. one for the voltmeter, other for the terminal and one for the potentiometer.
Then glue them all to the case and cover the connections with tape to avoid short circuit risk.
I didnt have any knob on hand, i recomend you to use one for a better appearance.

Step 5: Final steps

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Now solder the 30v output of the adapter to the converter input and cover it with more tape.
Then close the adapter with everything inside and glue the case with a strong glue as epoxi or cyanocrylate.
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MechEngineerMike made it!1 month ago

Hey, I was inspired by this project enough to make my own little version. I used a slightly more expensive voltage regulator than yours, but mine had a screen built in. I designed a 3D printable case for it too because I didnt want to try cracking open the adapter case. You can check it out here if you're interested:

http://www.thingiverse.com/thing:745463

IMG_1547_preview_featured.JPG

Nice project, this looks like something that would be really handy to have. Your graphic on step 3 looks good too, what program did you use to draw it?

pinomelean (author)  MechEngineerMike2 months ago
I used photoshop, but any drawing program would do.
Could I use other terminal? Like a Weidmuller?
jongscx2 months ago

I love that you're reusing the plastic casing of the PSU... Brilliant!

RC322 months ago

Hello,

Can you tell me how does it work, what we are actually doing. Please provide a detailed explanation.

Thank for help.

pinomelean (author)  RC322 months ago

The little board is a switching converter, you can look for the theory behind it. What you have to know is that you can put a voltage on the input, and the output will go from almost 0v to the imput voltage minus 2v, just by turning the potentiometer.

RC322 months ago

How did you decided to use a 10k potentiometer?

pinomelean (author)  RC322 months ago

Use the same value as the one that came in the board.

RC322 months ago

Hello,

Thanks for the inscrutable, it was a very nice instructable.

I have a question, my printer adapter has an input of 200-240V but in the you uploaded it read as 100-240 V; will my printer adapter work?

Another question, can you give the link from where you bought the components, because when I searched it on ebay it showing product costing more than you specified.

pinomelean (author)  RC322 months ago

If you live in a country that has an outlet voltage of between 200 and 240V

http://www.ebay.com/itm/1-DC-DC-Buck-Converter-Ste...

http://www.ebay.com/itm/Lithium-Battery-Digital-Vo...

MMelfe1 year ago

very good Instructable, but i have one question, i would like to use my old laptop charger but in output signal have 4.97A, can i use that DC-DC buck converter which his max A is 3A without problems?

luzzyf MMelfe4 months ago

Yes, no problem. Your circuit will only draw current (amperes/A) as needed from your 4.97A PSU. In fact, having more current capacity than required by the circuit is ideal as long as your load does not draw more current than the safe limit of ~2.5 A (the 3A limit of the buck converter's LM2596 IC should never be reached - especially not without a heat sink).

yoyolo7 months ago
Where could I solder an amp meter to this board?
yoyolo7 months ago
Any way to get an on off switch on there?
dkime7 months ago
what if i wanted ac output? specifically 9-12v at 1500-2000ma?
pinomelean (author)  dkime7 months ago
This circuit only works for dc, for ac you'll have to find something with a variable transformer, there i can't help you.
jymsie8 months ago

Hello everyone,

does anyone know how he does thet graphical drawing?

could you use a 20V power adapter, and get smaller hardware?

mmohtesib10 months ago

I made it ...after that I do not know what went wrong but my buck converter get burned :(

cooco10 months ago

I need assistance. I want to build this, but i require it to have 4 separate voltage settings. like.... a multi-variable voltage power supply. So each and every out has its own voltage. Do i just put more dc-dc buck converters onto the power supply?

pinomelean (author)  cooco10 months ago

Yes, you can simply add a converter for each voltage rail you need, i don't know how well they will perform in that configuration, but it's worth it to give it a try.

cooco pinomelean10 months ago

Awesome. Im hoping to build something similar to an e-hookah with this setup. Not sure if the ampere will be enough, but for the price, its definately worth a try. Also thank you for the quick answer!

mlocke made it!1 year ago

I used different packaging but the componants and circuit is exactly the same as your 'ible. Thanks for posting.

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Really nice Instructable, also very portable which can be useful.

I've been thinking about making one of these but maybe with the power supply built in just so I can carry it around and use it as a power supply. Probably just chuck a 9V battery in there; get a bigger enclosure if needs be.

gkal made it!1 year ago

Excellent instructable. Case was hard to close but finally did it. Put the connectors to the side. Thank you!!!

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akumar1591 year ago
Hey this looks great and want to make one, but quick question i have a old laptop charger and on the details its got

INPUT 100-240V ~ 1.4A 50/60 HZ
OUTPUT : 19V-- 4.74A

Im a bit of a noob at all of this but what output voltage would i be able to get or is this determined by the D-DC buck and the potentiometer?
This is odd. My computer adapter has the exact same specs. When I use this adapter with my "pinomelean" power supply cranked up to max, I get 100% of the voltage (19.2V) at the output. There is zero drop in voltage. (That's a good thing.) I checked with 3 different multimeter. I am using a multi-turn pot, instead of a single turn, but I don't think that matters.
pinomelean (author)  akumar1591 year ago
You can get 17.6v as maximun.
Is that because the buck converter is 92% efficient?
pinomelean (author)  iq2011 year ago
Buck converters are always working, so they output a maximun of Vin-1.5v
dbyrd261 year ago
The terminals are your positive and negative outputs I believe.
pinomelean (author)  dbyrd261 year ago
Yes.
tgaffney11 year ago
step up or step down converter
pinomelean (author)  tgaffney11 year ago
Buck=step down, but you can use an step up/boost converter if you want.
what are these terminals for??? check out the links https://www.dropbox.com/s/pmsxaq6ye13ziii/IMG_20131225_150954.jpg even check out this video https://www.dropbox.com/s/huppsfa1dcn2e6n/vid.3gp plz reply fast..need ur help
pinomelean (author)  swapnil20251 year ago
I don't know what those terminals are for, mine didn't have them, maybe for an on-off swich or something.

I can't really tell why the voltmeter isn't working.
Try to connect an external voltmeter and see if the converter works correctly, if it outputs the whole range of voltages, better buy a new panel voltmeter.
But if the output voltage doesn't work, replace the buck converter.
output is coming uptill 5v but after that there is a sudden drop in voltage to 2v even if the resistance is increased and the display doesnt work it just starts blinking after 5v?plz reply early
pinomelean (author)  swapnil20251 year ago
Check the voltmeter measuring range, some ones can't measure under 3v.
Is your converter a buck one? What's your power supply voltage?
be sure you have connected the pot in the right way.
i i bought this digital voltmeter display

http://cgi.ebay.in/ws/eBayISAPI.dll?
ViewItem&item=331073484894#ht_500wt_1156

and this dc-dc buck convertor

http://cgi.ebay.in/ws/eBayISAPI.dll?ViewItem&item=171185642573#ht_1808wt_1139

my input power supply is around 20v for the buck convertor

is there a specific way to attach the pot...i mean about two end terminals ..?????
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