Picture of Add a USB Power Outlet in Your Car
Given the bulky nature of 12volt adapters for vehicles, I decided to integrate a USB power outlet in my 2010 Prius III. Although this mod is specific to my car, it can be applied to many cars, trucks, RV's, boats, ect.
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Step 1: Finding a location for the USB power plug

Picture of Finding a location for the USB power plug
In the 2010 Prius III there is an unused outlet next to the 12volt aux power in the front center console. I disassembled the center console and removed the plastic housing of the blank outlet and the 12volt aux.

Step 2: The USB 12 volt car adapter

Picture of The USB 12 volt car adapter
I disassembled a Dynex USB power adapter and removed the circuit board from the plastic housing, then removed the 12 volt supply wires. The supply wires were springs and such, and too bulky to reuse.

Step 3: Preparing the blank cover

Once the blank cover (plug) is removed, I found it to be filled with a dense lattice of plastic. To fit the USB power circuit in it, a lot of the plastic needed to be cut out. Using an Exacto knife, and a box cutter, I cleared the inside of the cover.

Step 4: Fitting the USB circuit board

I used a Dremel tool with a grinding attachment to slim down the USB's circuit board until it slid into the hollowed out cover. Once the fit was right, it was time to make the hole on the face to access the USB plug.

Step 5: Making the hole for the USB power

Picture of Making the hole for the USB power
I approximated the center of the USB plug and drilled a tiny hole through the face of the blank accessory plug.

Step 6: Wiring

Picture of Wiring
Once I trimmed the opening, It was time to wire the 12 volt power to the USB adapter. Since the 12 volt accessory was right next to it, I soldered the ground from the USB board to the cigarette adapter, and attached the positive end to a nut on the back.

Step 7: Fixing the LED

Picture of Fixing the LED
The USB board has a 2 color LED to indicate power and charging. I wanted the light to shine behind the USB plug, so I de-soldered the LED and repositioned it to face forward. I had to add some wire to the board to attach the LED, but it was not hard, and could be done by a beginner.
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great job. don't worry about the spammers, you had a problem and you found a way to fix it yourself. you even inspired me to do the same to my car this weekend.
志灵刘6 months ago

Come on guys,use this!!Make everthing so easy!Contact me!!

schwag277 months ago

any thoughts on how to take one 12V cigarette lighter in a 1988 jeep wrangler, and modify so I can keep the cigarette lighter socket but add 1-2 USB chargers?

eatkabab8 months ago

How do you remove that panel from the Prius!? I can't get it off! I don't even know what it's called to search. I've tried every term I could think of... Please help :-(

Archbid1 year ago

I would recommend a different USB part:

It is panel mount, so it will look nicer and is self-trimming. It has two USB ports and has leads so you don't need to disassemble or hack the part. It just works.

Most importantly, it is rated at 2.1A (max you want to go on a 10A 12v circuit is about 3A), so you can charge iPads or charge iPhones 2x faster.

Rvinyl1 year ago
Great work!
joeynovak1 year ago
Holy Crap, what a bunch of haters and nincompoops...

Awesome Job! I like it! Following you...
Great idea but execution lacks craftsmanship (eg, USB cut-outs looks like a literal hack job) and doesn't provide circuit protection. Perhaps a reasonable variation is to add an in-line fuse holder (
There's no need for a fuse, it is just as protected as it was when the adapter was plugged  in to the socket.
I don't know about the Prius but my car's cig lighter fuse is rated to 10 amps. My USB power adapter's 1 amp fuse will blow long before the car's 10 amp fuse.

(BTW, I specifically looked for a circuit-protected USB power adapter. Some have fuses and some have circuit breakers. The biggest surprise was finding several expensive models that have no circuit protection at all. Buyer beware!)

Considering my car's circuit, adding an in-line fuse to your design costs $5. Better to spend a little for protection than to risk ruining expensive electronics.

But I guess it's ultimately your choice. Good luck! ;^)
Yea, I fried a $500 GPS because of that. You made a very good point. Hopefully someone wont make the same mistake I did. Dont assume anything is protected. Its always better to have too much than not enough.
Most of the USB chargers available today have small SMD resettable fuses which are similar to what is on the arduino boards.
and the socket is plugged into a fuse. also, if I remember correctly, the USB chargers have built in fuses too...
the 12v line is fused in the fuse box of the car susualu (unless your cars from the 70's) and the 12v plug has a glass fuse inside the barrel. but another 10amp fuse would be a good aditive for a bit more piece of mind. when doing something like this you should add your own 10amp fuse on positive BEFORE is splits to the 12v plug and the usb to prevent too much current being drawn if your cars 12v line isnt fused, you dont want to pull too much power and cook the wiring loom, could be nasty.
A 10 amp fuse is way too high for this. Your car may have a 10 amp fuse for the 12 V outlet but your USB device only wants .5 amps or so. If you use a 10 amp fuse you will risk killing your USB device or causing a fire if something happens because a USB device will never need 120 Watts of power.
hintss mdshann4 years ago
exactly, so, 120 watts won't reach it.
Generally there is a need for a fuse, in the method shown here, all power is guided directly to the PCB so there is no direct protection except for the general fuse box in your car. In most car USB adapters, the fuse actually is the contact tip of the connector. By bypassing that, you will end up without a fuse. By putting a fuse near the charger, you have a better protection. Let's assume you get a short-circuit in the charger, so it gets an enormous amount of current. Your car's wiring can only sustain a certain maximal current so eventually they will burn (and according to Murphy's law they will burn at the one place where it is hard to get to, hard to notice and hard to replace). So expect quite a bill replacing these wires. With another fuse, only the fuse melts, you check/repair the charger (which is really easy because you have a fusebox in between), put in another fuse and there you go. All minimal cost and perfectly safe. Also for safety, I recommend NOT to put in a 10A fuse (like it_dont_work says). Putting a fuse with too high a value is not a good protection. Because actually a 10A fuse will not cut the circuit when you hit a peak current of 10A. It will only cut the circuit when you have pulled 10A for a longer period (let's say 2 hours). Or it will cut the current if you pull e.g. 15A for a short period of time (few seconds). If your USB charger pulls more than let's say 5A, there is something very wrong. A USB charger doesn't need 12V 10A (which is 120W, enough to power a notebook), according to USB specs, on the USB side you will get 5V 0.5A (2.5W); but let's assume your charge doesn't quite follow that and gives you about 5V 1A (5W) output. So limiting the fuse to, let's say 24W is generous (keep in mind, we need to be a bit generous: you still have to power the circuit that converts 12V to 5V and a circuit generally needs some headroom for variations in temperature, voltage swing, start-up, ...). So 24W on the 12V side, that's a 2 ampère fuse; which I think should be enough (I haven't tested it, but you could easily measure the current with a multimeter). Another way of determining what you might want to put, just take the fuse that came with the charger in the first place; you can safely assume the people who put the fuse there, knew the rules in choosing fuses.
jvan tonder3 years ago
You can buy a finished USB power adapter for this purpose for about 14 Euros on Amazon. No need to tinker:

isnt it fun making something just because you can?????????
conman4 years ago
So let me get this straight, you hacked a USB outlet in to your Prius so you could use your hacked USB cable? Instead of not chopping up your cable you bought, and using it with the manufacturer provided outlet 2 inches away? Sounds about right for this crowd. Nice instructable!
Achan20 conman4 years ago
but what happens when you need to charge your cell phone and power your GPS at the same time? lol
aed38104 years ago
Did you need to do anything to the power supply to the cigarette lighter or were you able to attach the wiring from the USB adapter straight to the live, ground and neutral of the lighter unit?
rosenberger31 (author)  aed38104 years ago
I just tapped into the cigarette lighters power. When the car is off, there is no power supplied to the accessory outlets, so the USB plug is powered off. (see step 6)
TanPotato4 years ago
The USB circuit will have a current limiter built into the IC for probably 1.5A max or so. There is no worry about it pulling too much current from its input.
moorea74 years ago
What I'd be tempted to do is hack a powered USB hub into the car by way of replacing the power supply with an appropriate DC-DC converter. I can get USB extension cables all over the place, so I could mount USB ports all over the car if I so wanted. I could then add a usb -> computer port on it so I can hook up a netbook and use the same hub for doing things like adding songs to the iPod. Also, with a little more trickery, you could add additional devices - ipod to car stereo comes to mind.
prodlad5 years ago
i would suggest adding a switch because the cigerette lighter in some cars is live all the time. So you could end up coming out to a car with a flat battery.
rosenberger31 (author)  prodlad5 years ago
Almost all cars made within the last 15 years (especially foreign) do not power the aux/cigarette outlet when the car is off. I did not need a switch for this reason.
Not true. In almost all cars I've been in, the cellphone charge cable stays functional even after the car is turned off.
well in britian some cars do, and pickup trucks and jeeps espically power there aux outlet.
Padlock prodlad5 years ago
You would either would have to have one heck of a USB charger, a very tiny battery, or never ever use your car.

Besides, it's a hybrid = Ton's of batteries!
adaviel Padlock5 years ago
The 2007 Prius has a tiny 12V lead-acid battery to power the control computer, lights etc. The main battery is a 200V NiMh pack. I forget if the 12V will charge from the 200V without turning on the ignition; I think not. The ignition "switch" is a smart device that talks to the computer, which needs 12V to run. There is no way to charge the 500V from the 12V - f you somehow manage to drain the 500V one flat there is no way to jump-start or even bump-start the car; it has to be trucked to a dealer and the battery swapped out.
But I think if you drained the 12V by leaving your MP3 running all year you can get a jump off a passing moped, or charge it on a solar panel enough to boot the computer.
Your Prius will not charge the 12v battery when it is off.

If you park your car in READY mode the engine will cycle on as needed to recharge the main traction battery, and the main traction battery will supply power to keep the 12v battery charged.

Have a look at  I use Richard's approach to draw power from the main traction battery and can verify that the engine keeps it nicely charged when in READY mode.
Padlock adaviel5 years ago
The last part was kinda like a joke...
zack247 prodlad4 years ago
my dads 04 ddge ram 1500 quad cab does, the neon lights he put in the air vents can be turned on if the truct is off. i think this is for fogligts or something
 I installed a 1.5 watt solar cell in my car because of the charger for my gps unit being live all the time.  The 1.5 watts seems to be enough to keep the battery from being drained, allows me to lazily leave my gps in the car, and only cost me $20.  I recommend it for everyone, and you can get a 5 watt model for just a little more if your setup demands it.
be great for me as i tend to leave my headlights left on, on dull days, nice idea fellow invader zim lover.
led235 prodlad4 years ago
 my car has 4 cigarette lighters, and a 120 volt plug in it, 2 cigarette lighters are onto the battery, the other two as well as the 120 volt plug are for the ignition. 
static prodlad5 years ago
 Not an issue because the dynex unit used auto powers off.
Looks good- my only recommendation would be to use a panel mount USB jack for a cleaner install. 
Jayefuu4 years ago
Nice work! It could be prettier but all the detail is there in the ible to show people how to do it if they want to. You're right about this being better than the 12V plugs, they're SOOO bulky. 5* and a great first ible. :)
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