USB Car Charger




This is a Home Made Usb charger with this device  you can charge in your car any Usb charged device like mobile phones, bluetooth headsets, Gps , cameras, mp3 players, etc..
This device I made haves 0.5Amp output that is the normal power output on a computer, if you use a bigger transistor you can  get more output amps.

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Step 1: Parts & Tools Needed

This are the parts needed to assemble this home made USB charger:

-cigarette lighter plug
-Usb female Port  (taken from a old computer Motherboard)
-5V regulator, 78M05 or 7805   (taken from broken playstation, you can take from other broken device or buy)
-resistor 100 Ohm or 220 Ohm
-Heat Shrink Tubing

-Solder Iron
-Solder lead
-Solder Paste
-Hot Glue Gun

Step 2: Schematic

This is the schematic

The standard 7805 was to big to fit inside my cigarrete lighter plug.
So i used the 78M05 a SMD transistor because is smaller then standart 7805, and haves 0.5A that is enough for the USB charging.

Step 3: Cigarrete Lighter Plug Drill

I made this holes with the Dremel to fit the the USB female .

Step 4: Soldering Parts

In this pics I show the transistor and wire setup

Step 5: Soldering Led's

This Pics show final circuit with the Led already mounted
I Used the Heat shrink tubing  to isolate some soldering points

Step 6: Fit the Circuit Inside Plug

I this part I used the Hot Glue Gun to glue the Usb Female on the back of the cigarrete lighter plug.                                                                                           

Step 7: Finished Product

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    23 Discussions


    2 months ago

    Hey friends,
    I made that circuit. Its working. I can charge my Bluetooth head set with it. But when I try to charge my phone with it it's heating very mush. What. I can do for it?


    2 years ago

    For those who are asking about high heat dissipation or unable to charge
    device. LM7805 does not magically converts 12v to 5v. It will
    dissipate the 7v as heat. It rapidly changes it's resistance in while
    maintaining a fixed ratio of res(7805) : res(load) to Volt(IN)-5v : 5v.
    For example if input is 12v and load resistance is 5ohm (i.e. 1A load
    current @ 5v), the ratio of resistance will be (12-5) : 5 -> 7 : 5,
    thus 7805 will have a resistance of 7ohm when input is 12v and load
    current is 1A. At 41.6% efficiency a 5W load will appear 12W load to the
    battery. However it is more preferred than efficient SMPS when the
    output voltage has to be extremely stable or when energy consumption is
    low or when energy is cheaper than the IC itself. For those who wish to make a very simple, cheap & efficient SMPS i would suggest them AD84064 ic or more common 34063 ic (w/ 2 more resistors to add than AD84064).

    omprakash sahu

    4 years ago

    Hi I am try this circuit using 12v 1amp DC adaptor. But 7805 voltage regulator produce large amount of heat.
    How can solve this problem.


    Mine doesn't work, I'm running it off of a dirt bike for a camping trip useing a L7805CV and it won't charge. I'm only useing the led and the usbs in the picture, not the button. know I have the pins right. And both lights work.


    5 years ago on Introduction

    i couldn't really get it to work....bcoz i have it connected to a solar panel with a 15 volt output...n when i connect it to a phone, it doesn't charge....basically, when there is a load, the voltage drops. plz help

    1 reply

    Hi there, I did this same thing and mine didn't work because the solar panel doesn't create enough current to charge my phone...the best bet is to plug it into a 12v power source from a battery or indoor socket adapter and check to see if ti is working; if it does you know why the solar panel will not work.:-) I know it has been a year but hope this helps.


    5 years ago on Introduction

    what about DC chokes and stuff? i dont want my alternator to be feeding into my devices usb. also i would reccomend a computer heatsink, these regulators can put out bonkers heat.


    5 years ago on Step 2

    Does your charger get REALLY hot? I made one like this and it gets so so hot. It has to dissipate so much engery to take the 12v to 5v... How do you solve this?


    6 years ago on Step 2

    Shouldn't the data pins of the USB be shorted together, to indicate it's a dedicated charger?


    7 years ago on Introduction

    I've found an easier solution. Browse any discount store for car cell phone adapters. Some cell phone batteries charge at 5.1V and 550mA. Perfect for a straight across USB splice! And don`t forget the sugru.


    9 years ago on Introduction

    No one here really has thought this through properly. The 7805 should be heat sinked. Its not so much because of the current the 7805 is supplying to the usb connector or external device being powered that I am concerned with. Its the fact that the device takes the 12 volts or more from the car power and drops it to 5 volts. That is a drop of 12-5=7 volts. The 90 or 95% efficiency has to do with how the 7805 handles the droping of the voltage. If the device you are powering is 200ma, and the 7805 is 90% effient, that means you need to draw 200ma x 1.1 to get that current out, or 220ma into the device. Now take the drop of 7 volts x the 220ma=1.54 watts of heat produced by the 7805 in dropping the voltage. (Volts x Amps =WattsPwr) Now 1.54 Watts does't sound like much, but that will get the 7805 pretty darn hot. If you check the 7805 data sheet and do the calculations, I think you will see that a heat sink is needed. especially for the lower power version.

    1 reply

    Reply 7 years ago on Introduction

    im surprised noone has commented your post. youre absolutely right. that was also what i was thinking. Ive used the 7805 before and even though it was for moderate use, i heatsinked it and didnt have any problems after.


    9 years ago on Introduction

     LM7805 are VERY inefficient.
    In order to bring the voltage down to that 5V it releases all the extra in the form of heat, and they get VERY hot at 12V, even though they can go up to 46V.
    since an lm7805 is inefficient it will drain your car battery as quickly as if it was a 12V device plugged in, wouldnt recommend using this if your car isnt on.

    I took apart a bunch of car charges I have just to find out which ones were the good quality ones, one of them had a lm7805 and it had melted a bunch of the wires, and part of the casing on the inside.

    2 replies

    Reply 9 years ago on Introduction

    Thanks for the tip  I am going to make some measures on the power consumption and temperature, to check that. If I conclude that you are right than I will try to investigate how to make a more efficient one.
    For my practical use is just to charge my bluetooth headset sometimes for that purpose is not going to be a problem.

    Thank you one more time for your comment.


    Reply 9 years ago on Introduction

    I think the 7805 will become very hot if you were to step down 12V to 5V. I will highly recommend using the LM2576-5.0 for this purpose cos the efficiency is way higher and I think it costs slightly more than the 7805.


    9 years ago on Introduction

    well shoot, accidental page refresh killed my well thought out post.

    Guess I'll summarize.

    Don't worry about inefficiencies.  at max draw, on a 40Ah battery, it'll take 2 weeks, just to drain the battery of charge. Presuming the device is constantly charging. 

    Here's the math.
       Spec sheet for the 78M05 shows a output limit of 100mA. average led, 20mA. Parasitic loss of the 78M05, 8mA. Total MAX load with the device plugged in, 128mA.
       40AH starter battery average=40000mAh
       40,000mAh(battery)/128mAh(device draw)=312 hours to drain a battery.

    Now, With JUST the charger plugged in, you've still got a drain. Close to 30 mAh.
    That's pretty significant considering the draw with a charging device. But, it's still gonna take a good long time leaving it plugged in to drain the battery.  Consider that self-discharge of a starter battery is 2mAh a day. So, the device alone draws 15 times the energy of unhooking your battery cables, and letting the battery sit in 70F weather. Not too bad :-)

    If you're looking for a device to plug in to permanently wire into your car for usb charging, this might not be it. If you're looking to leave your device charging for long periods, with the car off... this might not be for you. If, you want a simple to build usb car charger made from spare parts, and are willing to unplug it when not in use, then This might be for you.

    4 replies

    Reply 9 years ago on Introduction

    o, I did read wrong on the spec sheet... the lm78m05 is capable of cranking out 500mAh. So, it could drain the battery at close to 1% per hour. So, don't charge multiple  high amp-hour devices in a row, without running the engine. A fully charged battery(say, parked after driving to work) and leaving 4 Samsung Moments(my new shiny android phone :-) plugged in and charging(from EMPTY)... when you come back out, they're all charged to 100%,and you're battery has burned approx 10% charging them.

    Normal starter motors look to draw about 150 amps. Soooo...
    Trying to start a car in the cold for 2 min burns about the same battery capacity as charging my phones from 0% to 100% 4 times.  Since MY average crank time in dead of winter is 15-30 seconds... and I usually charge my phone when it hits 40%... One good crank = 1 phone charge = no a problem in my book :-)

    Good job on the 'ible, by the way :-)


    Reply 9 years ago on Introduction

    Car batterys are not capable of 40Ah...what your looking at would be a deep cycle battery.
    Car batterys are made for delivering a lot of amps for a very short time, enough amps to create the spark to ignite the fuel, a constant drain on them damages them and drastically shortens there life.

    Also, the LM7805 has a 1Amp output.


    Reply 9 years ago on Introduction

    the LM7805, yes, fully capable of 1A service.

    The LM78M05 , not so much.
    The small package has "Output current in excess of 0.5A"
        with normal heat dissipation, 0.5A is max for that chip.
        It CAN be pushed to almost 0.7A with additional heat sinking, but that is
        outside design specifications.

    You are MOSTLY of right on the car battery issue.
    A NORMAL starter battery shows a 135 min reserve capacity(went and looked it up, because of your accurate observation). Reserve capacity is the time in minutes that a new, fully charged battery will deliver 25 amperes at 80 degrees F and maintain a terminal voltage equal to, or greater than, 1.75 volts per cell. Similar to the conditions I described in my initial comment. Netting that battery just over 2Ah@12V. Given that, and a 1A 7805 circuit... you'd have a dead battery when you left work.

    MY car battery is actually has 15 Amp Hours at a 20 Hour Rate. For a little light reading on the matter follow this link.
    Now, to be fair, MOST people don't use a large truck battery in their 1L subcompact(heck the battery weighs almost half what my engine does! 60lbs vs 118lbs).... and deep discharging with this style battery does shorten it's "expected lifespan under normal usage". HOWEVER, it's not as terrible as you seem to think, especially at low loads, without deep discharge, and with proper re-charge practices(read occasional de-sulfination charge cycles).

    To put a fine point on the matter, I actually know a fella that uses starter batteries in his electric car. Sure, "they're totally dead" after 2 years of mild use, but he gets them from the scrapper for the exchange of his old batteries, so essentially free. He uses twice the number of batteries as his wife's car, with deep-discharge golf cart batteries, and doesn't get as far on a charge. But it does work(and hard to beat FREE).


    Reply 9 years ago on Introduction

    So, this morning, I decided to TEST this.

    Grabbed my old starter battery(no treatly kindly during it's life of service).
    Charged it up(12.4Volt measured after surface charge was bled off).
    Wired a cigarette lighter cord up to a heat-sinked(6 oz of finned alu) 7805.
    Grabbed the old 6volt1Amp weed-eater(battery long since dead)
    Wired it into the mix.
    Velcroed the trigger down(on) and started a stop watch.

    Now, the battery manufacturer claims 81 minutes reserve capacity.
    So, when new, it should be above 10.5 volt after running that load for just under 3 hours.

    MY results... after 6 hours, the battery still showed 12.1 volt left...under load!
    So... judging by new battery standards, I burned down from 75% to 25% remaining "safe capacity".Voltage is still rising back up, with the load now disconnected, so I don't know what actual percent burned off through the motor/IC.
    All on a battery that is so toasted that it has to be tickle charged(the fast charger return "it's dead. go get a new one" message)

    Conclusion : Go for broke.
      Unless you already have a battery problem, the 7805 charger circuit isn't gonna make a significant dent, unless something's gone horribly wrong.

    P.S. No, there was no danger in running the trimmer like that. It had no string left. I suppose something COULD have melted, and would have smelled bad, but the concrete is fireproof so....