Cheap and Simple USB Car Fast-charger Mod





Introduction: Cheap and Simple USB Car Fast-charger Mod

About: The pre-neopostmodern electro-Amish man using sense and caution when voiding any warranty.

A few years ago I had to make a fairly long road trip. Around 8 hours each way. I typically use my phone to provide music through the aux jack on my stereo, and when I travel to parts unknown I also use my phone for GPS navigation assistance. On this particular journey I had also planned to play with a new bluetooth gadget that I had just purchased.

Obviously, a phone simultaneously running 3G, bluetooth, GPS, & playing music uses a lot more power than a sleeping phone running no services lying on the seat. I soon discovered that my off-the-shelf lighter-plug car charger would not provide sufficient current to keep up. Even when only using the GPS my phone's battery was draining. After several purchases of progressively more expensive chargers I finally broke down and did some R&D.

I've since built a multi-port linear supply from scratch into the dash of my truck, but my wife wanted a no-dash-cutting solution for her car.

...more on the bigger linear supply charger in a separate instructable later...

Step 1: Background

You may have noticed that your device charges faster when using a wall charger than when using a car charger. On some set-ups that charge through USB you may have also noticed that your device knows the difference. There may be a different icon displayed when charging with one than the other. The reason for this is that some devices can charge at different rates under different scenarios.

To simplify the jargon and only address what's necessary for this article: The USB standard provides for a non-data charging connection that will provide higher current. You can get the full rundown at wikipedia

I'm going to disclaim here for a second: I'm not responsible if you melt down, electrocute, or violently explode your very expensive device, your car, your home, or your dog. These are all very real possibilities if you misuse or make any alterations to electrical devices. Use sense and caution when voiding any warranty.

That being said, the method that devices use to determine when they can charge at a higher current is through the USB connection itself. A standard USB type-A connector uses 4 pins: The 2 outside pins are for supplying current and the 2 center pins are for data. If the center 2 data pins are shorted together then it is obvious that no data can flow. This is an indication to the device that it can charge at a faster rate.

Step 2: Mod

I've found a car charger that, once modified, happily provides me with enough current to run all of the services I want. It appears to be rebranded and sold by a number of different vendors and is readily-available for under $10 at just about every chain store and interstate truck stop I've visited since. Another advantage it has over some other chargers is that when it is installed it sits back flush enough to the receptacle to allow the ashtray door to close. When selecting a charger to perform this mod on be mindful of the output current. The higher the better.That in and of itself won't charge your device faster, however. You still have to alter the charger. Personally, I would not perform this mod on anything that is not capable of providing at least 1 amp.

Once you have the charger in hand the mod is simply this: open it up, solder the center 2 pins together, and put it back together.



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    33 Discussions


    1 year ago

    Question: Fast Charges Qualcomme 2 exist today. did you try changing your car usb to one that have this chip? Apparently i couldn't find one article that talks about that. The problem is It's either I have to use the my car charger to charge fast or use Android Auto to mirror the phone but loose the fast charging and in those new phones No fast charging is a pain

    1 reply

    Chargers supplying 2 amps and more are pretty common and really inexpensive now so I've just been using a cheap 2.5A. I had an antique truck that I'd made a linear supply using an LM series chip and installed into the ash tray. Soon I'll likely either be making another of those or disassembling a cheap charger and installing it directly into my dash. The cigarette plugs aren't the most stable or secure connectors and mine come loose fairly frequently.

    szc kj

    1 year ago

    You do not specifically mention if the device you are referring to was modified.

    Thanks I found your tips very useful. But we can do this in the USB cable and then use the cable anywhere (by shoring the Data+ and Data- pins on the output side). Also on some Android ROMs like SlimRom you can enable Fast Charging mode in software.

    NOTE: I have used "Charger Doctor" to monitor USB output currents in various configs and have found the slow charging culprit: "A Bad USB Cable!" The cable I used was 60 cm long and dropped both the voltage to 4.5 volts and the current to 0.19 amps while charging my Samsung Android phone (AC charging mode)!

    The stock USB cable that came with my phone allowed 0.49 A in the USB mode and 0.65 A in the AC USB charging mode.

    -Bad USB Cable (~60cm long):

    USB Current Measurement: 0.15 A (USB) - 0.19 A (AC-USB)

    - Stock Samsung USB Cable (~30 cm long):

    USB current measurement: 0.49 A (USB) - 0.65 A (AC-USB)

    So the USB cable is very important. The shorted the cable, the better.

    4 replies

    II don't like the idea of a shorted cable first because the cable can no longer be used for data. Outside the car tricking the device into fast charging from a port that is not designed to handle it can potentially damage that device. Inside the car the charger is the logical place to make the modification because the charger only has 1 purpose.

    Thats been my concern with shorted cables. A computers usb port can only supply 500 miliamps at most, but a shorted cable would trick a device into trying to draw more than the computers port can handle and fry a component. Secondly, when I need a data cable, I dont want to mistake a shorted usb cable for a data cable.

    Length can impact the charg rate. So can the diameter of the wires as well as the type of metal in the wire (copper or aluminum), of the cable.

    Each parameter above effects a cable's internal resistance, thus effectively creates a voltage dividing network with your phone that ultimately draws less current and delivers even less current.

    I bought a USB charger doctor for less than $3 on ebay. They are extremely handy.

    Also, don't forget that your Samsung phone (Galaxy or Note I'm assuming) charges at a higher current with the screen off so you are missing out on this information keeping the screen on. My S5 pulls around 1.1a with the OEM charger with the screen on and 1.7a with the screen off.


    There are reasons why it didn't come soldered. One is although it can supply with 1A the chip will run hot and will not last long, within hours it will just failed and gives out full 13volts of whatever fuse rating you have. If your device is smart enough it will shut itself off, if not you will have a fried device.

    8 replies

    As you can easily see, the device is rated for 1.5A continuous. The reason it didn't come soldered, is because in the early days of USB charging, smartphones use different voltage divider networks on the data[ins, to tell the device how much current it could supply. This standard has since been abandoned, and we now use the standard as written by the USB-IF, that says a dedicated power device, shall have the two middle pins shorted to signal that it's a power supplying device.

    I tested a couple car chargers that I have and they proved to put out almost max amps over a good quality none data shorted cable. I bet if I opened it up the data pins would be shorted just like this instructable states.

    No need to open it up. Take a multimeter to the data pins and measure either a short or an open

    Fair enough, though I think you're off the mark in a number of places. It is only the very slimmest of chance that a failure in the power supply will result in full supply voltage (13VDC) making it to the output. It is far far more likely that the supply will fail open and supply 0VDC. Also you will notice that this Instructable was posted 2 years ago and starts with the phrase "A few years ago...". The road trip I mention was taking my now 21 year old son to Baylor college debate camp when he was 16. I am still using the exact same charger in my car. For 5 years I have driven an hour each way (2 hours total) to work with my phone plugged into it and playing music through the stereo. When he turned 18 he moved 4 hours away to college in KCMO and I visited him at least once a month, but usually twice. I would have the phone connected to the charger, playing music, running GPS, and usually running tethering for my wife's tablet. Point being that the charger was getting a workout and experienced no ill effects. The charger pictured in this instructable was one I modified for my wife's car - and she has been using it daily for the 2 years with no failure whatsoever as well. I have modified 4 or 5 for friends who use them daily - not a single failure. So interpret that data as you will.

    A failed semiconductor will either become non-conductor (open) or conductor (closed with low resistance). I had one of this car charger supposedly can output 2.1A of 5V. It wouldn't charge my tablet in the car, though the tablet software is showing charging. I hooked it up on the bench to monitor the voltage and current, it gave stable 5V but the current is pulsing between 230mA and 460mA. Well this is typical of DC-DC converter but the IC is way too hot, over 90 degC using infrared thermometer. While still monitoring and using the tablet the IC failed, luckily the tablet had voltage sensing circuit and just shuts itself off. Now the charger is giving 13volts output with input of 14.5volts from the bench supply, totally useless but it didn't go off in smoke.

    Right - and as I said "It is far far more likely that the supply will fail open", and I stand by this. My reasoning is based on my own observations over a few decades, however. I also related how the modified chargers have held up in my experience. You do not specifically mention if the device you are referring to was modified. In your first post you allude to this being the case, but I'm not going to assume. Regardless, if the device is listed with a rating of 2.1A and it cannot functionally provide that current then the device is not operating properly. It is either incorrectly designed or damaged.

    You are 100% correct. There is no harm done when doing what your instructable suggest.

    You can even buy cables meant purely for fast charging if someone is unable to duplicate your process.

    Your arguments are logically flawed. Soldering the two data pins together is no different than buying a charge cable that already has those connectors shorted. You can use a charge cable on any USB port without causing any damage. If you're interested you can read up on them or even buy one here.

    Pretty good instructable. There is one thing though. If you do this mod, you will most likely not be able to charge apple products. This is because you need each of the solder points you soldered together to go to a resistor and then to ground.

    2 replies

    Thanks for the kind words! I had come across some info regarding the Apple charging spec back when I made my linear charger. Based on what I'm reading now, this *should* only apply to older (pre-2007) products that were made before the USB standard introduced dedicated charging ports. []. I would think that things manufactured after that point would have to conform to the standard. This makes me think that I need to have some of my iOS-carrying friends try the chargers.

    It makes me wonder then if all of the USB wall-wart supplies that have proliferated in the last few years will only charge Apple devices at the slower rate?

    I am pretty sure that even the newer apple products require resistors. I tried charging my ipod nano on a non-apple charger and it did not work. I opened up the device to find that there were no resistors on the data lines. Plus, my nano is post 2007. Anyway, good hack!