12V Car Lighter to USB Adapter for Less Than 3 $ (1,5euro)





Introduction: 12V Car Lighter to USB Adapter for Less Than 3 $ (1,5euro)

About: I like to invent and modify things. When i was 13 i fixed my dad's old Lancia Fulvia motor. I builded my first mod PC in 1991 using a mobo builded in a VCR box. I am first using all my inventions. I love eve...

I had a client recently wanted to use USB in his car. He told me that kind of adaptores cost in the stores about 13-15 euro (8-10 USD) the cheap and about 25euro (18USD) the expensive. That was a challenge for me. So i tried myself to do it.
First of all we have to consider what exactly we need to do with a USB as power supply. To charge an MP3, using it as light resource or other genberal power supply of standart 5,1 V DC.
The materials are...

1. A Car lighter adaptor (from 0,50 to 1euro)
2. One 12V lamp or a led and 330Ohm Resistor 1/4Watt (0,02 euro)
3. A USB Sasshi adaptor. (I had one from spare parts) New costs 0,20 euro
4. Two pieces of cable one black 10cm and one red 7cm
5. One resistor 57 Ohm 1 watt (0,01euro)
6. One diode 5V1 (5,1V) (0,01 euro)
7. one Cooler (0,10 euro)
8. Some soldering and a little attention.

Step 1: Lets Work!

First of all we take the Car lighter adapter. All of them have fuse of 3A. We leave like it is.
The Lighter Adapter i got had a trasparent red cover and then i had another idea. To put a small 12 V lamp to define if it's working or not.
The Positive pole is in most cars the central pin.
So we place the small lamp among the negative and the positive pin of the adaptor
Also we Solder the cables in the + and -.
After we close the car lighter. If we power on it shows like this (Image 3)

Step 2: Power Limitation From 12V to 5,1V

The Power limitation can be done with combination of in Diode 5V1 and one resistor 47Ohm 1 watt.
We combine both like in the image. The + Cable (RED) connects is serial mode with re resistor. We prefer 1 watt or more because the resistor gets hot when the circuit works. The cooler covers the Resistor for better results. The diode of 5,1V says to our circuit that more power than 5,1V is not allowed.

For the USB sashi we need only the edge left and edge right cables. We nude out the cables and we cut the rests. Usual the L and R cables are red-black. Now I will use these 2 cables to solder them with the resistor and the diode. The + goes to resistor and the - goes to the light bulb and the diode. So simple...Just beware of power conflicts!!!. Use isolate tape and isolate thermal tubes...are more effective.... If you have any box in small size like one from old flashes or other are ideal to cover the whole project.

So friends that was the project. Easy, Cheap and need

See You All Around



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    Thanks to PBen who observerd an error on the schematic I draw in earlier post....The Zener Diode is attached across to the source line the Cathode (-) is in the 12V and the anode goes to ground(-)....


    Great idea.
    I wonder if you would be willing to clarify just a bit ?

    1. The word 'sasshi' - does it mean 'socket' as in 'USB socket' ?

    The circuit is not drawn out and how you wired the diode is baffling:
    What did you do with the open end of it - where does it connect ?

    One must presume it is a ZENER diode, similar to:
    Digi-Key Part Number: DFLZ5V1DICT-ND - is that correct ?
    (Zener diodes usually are used by 'bleeding off' excess as heat or to ground...)

    The assembled item hides the resistor's heat-sink somehow; is it all taped up, or hidden inside the 12V plug-in part ?

    Please pardon my curiosity.
    I haven't used a zener diode for anything in almost 20 years and had forgotten they even exist anymore !!!

    Best Wishes, and Thanks.

    3 replies

     1. Yes my English need get better...sorry
     2. Look the image for schematic  sorry too I thought was obvious.
     3. Yes again
     4. I cover the connection of diode with the Resistor with black tape for obvious reasons The resistor it self is uncovered to avoid high temperature and then covered by a  sink


    omg you have right!!!!....I made it right but the schematic is indeed wrong ...sorry I have to fix it.......thnx

    ???? I missed something???

    I think it's "too short through the curve", as we say in the Netherlands. How about safety? I used a voltage regulater from the 78 series, only 60 eurocents at the local electronic store. Thermal and shortcircuit protected. It easely fits in the plug WITH a small glass fuse. And we don't need a light to see if it works, unnecesary lights can be confusing in a car. Otherwise I like this site.

    1 reply

    I liked the red light. It's soft and doesn't make any comfusion...The light adapter has a bulb fuser (the cover is red) and makes the light!!!!!

    You could use an lm7805. They are dirt cheep on mouser.com. Just wire the positive from the battery to pin 1, negative from usb and battery to pin 2, and positive from usb to pin 3. They will protect your usb device from overload.

    1 reply

    Most of the times the best ideas coming when you don't have some materials and special to me iI love work at night where the stores are close. Usually I proceed a project without plan....I am shiting on pange think a bit, drawing some basics on a piece of paper and then immediately I fix it. That's the way my mind works....I think what project make tonight and then I proceed...No plan...so many times I don't have materials and I use alternatives. Thanks anyway :D


    Just to note that the resistor shown in the pics is a 58Ohm resistor mate.

    1 reply

     Green-Blue-Black = 570 Ohm. I had only this size of 1watt so I use it. No problem cause the difference between these sizes is small. 

    It is a great exchange rate you get there like $ is stronger than Euro 

    1 reply

     No the exchange rate i placed is right....the Euro is much stronger than US dollar....1euro= 1,45 US$ so 1,5 euro= 2,1

    Thanks...That u said was a fine idea. I measured the circuit using a hub of 4 ports and all connected to charge something (like MP3 player, Cell Phone, a mouse, and a camera) The power that come to the Hub is around 4,7 up to 5V After all these connection the remaining power its up to 2,5 V... But when i connected 4 Leds of 1,7V each the remaining power gets to 0,32V!!! It seems by that that depends on what you are using for the Hub.. After all the tests were got clear enough results

    Nice and clear job. 5/5 Some pics are Blur but are clear enough to see what's happening. What if the sasshi usb you connect directly to a USB hub for more USB links? It influence the power???