Add a USB Power Outlet in Your Car

Step 9 Final install

I let the glue cure overnight. After testing the power out one more time, I slipped the plastic housing back into place. Nice!

Comments

[bonzobuilder]

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 (http://www.napaonline.com/Search/Results.aspx?Ntt=in-line%20fuse&Ntk=Keyword&Nty=1&N=0)

[alwaysworks]

There's no need for a fuse, it is just as protected as it was when the adapter was plugged  in to the socket.

[bonzobuilder]

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! ;^)

[jgregory83]

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.

[uberdum05]

Most of the USB chargers available today have small SMD resettable fuses which are similar to what is on the arduino boards.

[ILUsion]

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.

[hintss]

and the socket is plugged into a fuse. also, if I remember correctly, the USB chargers have built in fuses too...

[it_dont_work]

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.

[mdshann]

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]

exactly, so, 120 watts won't reach it.

[conman]

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]

but what happens when you need to charge your cell phone and power your GPS at the same time? lol

[TanPotato]

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.