USB Switched ignition power ideas

[cobra]

I have a USB powered device I want to be powered only when the ignition turns on. Right now I am just using a cigarette lighter USB adapter, but it's very annoying having the cable stick up near the shifter and unplugging it every time I park the car.

Any recommendations for doing a clean install for this? The device is mounted up on the center of the dash vent.

edit: One important factor is it needs about 10W of power, which some cheap USB adapters cannot provide.

[elrichmeister]

I wired my dash cam to the Homelink connector in the sun roof cubby thing. Its switched 12v source.

Also wired my Bluetooth/Aux and phone charger to the same fuse with Add a circuit in the fuse box and wired it through my sunglass holder

Fuse 26 in glove box

[bmwfnatic]

I would use a fuse tap, can easily be reverted, obvoiusly select an ignition controlled fuse for your use case.
Then get a 12v to 5v step-down converter, or honestly just gut the insides of the adapter you are using right now, then run the wires to your device.

[Cubieman]

This worked well for me, maybe not enough juice for your application however.

https://nam3forum.com/forums/forum/m...-power-sources

[bigjae46]

I hardwired two USB ports in the car then ran a cable to two GoPro’s. Never have to worry about battery…just need to remember to stop recording.

[sapote]

This worked well for me, maybe not enough juice for your application however.

https://nam3forum.com/forums/forum/m...-power-sources

Pin6 and 8 are 12v from 5A fuse for telephone supply, so this should be more than enough for 10w USB port. Note: this circuit below is only for cars from 2002/3.

Quote "edit: One important factor is it needs about 10W of power, which some cheap USB adapters cannot provide."
OP, I would wire up the current USB adapter to the said pin6 of the 18pin phone connector, then hide the usb bulky adapter under the console and run the usb output cable up the dash to your device.

[cobra]

Great idea guys! I will do it under the console and run the wire out from next to the passenger seat. Should look nice and clean.

[bigjae46]

Great idea guys! I will do it under the console and run the wire out from next to the passenger seat. Should look nice and clean.

I always recommend just using a switched 12v lead as a trigger for a relay. Then run any aftermarket circuits from the relay. Makes troubleshooting issues much easier.

[cobra]

I always recommend just using a switched 12v lead as a trigger for a relay. Then run any aftermarket circuits from the relay. Makes troubleshooting issues much easier.

I'd then need to run a power lead separately. If the wire gauge is good enough and it's fused at 5A there should be no issue powering directly off the telephone wire?

[heinzboehmer]

I'd then need to run a power lead separately. If the wire gauge is good enough and it's fused at 5A there should be no issue powering directly off the telephone wire?

Fuse 7 powers a bunch of other stuff too. Fuse 39 is 10A and will give you a little more headroom for power, but it's not switched by ignition.

Since you're already gonna be running a wire from the center console, I'd do what bigjae46 said and wire up some sort of relay underneath there to have the actual current draw come from fuse 39. I actually did exactly that and documented it in my journal if you want a reference: https://nam3forum.com/forums/forum/m...309#post195309

[bigjae46]

I'd then need to run a power lead separately. If the wire gauge is good enough and it's fused at 5A there should be no issue powering directly off the telephone wire?

Its extra work but well worth it especially if you need to power more than one device. Typically most will use a 12ga wire connected to the battery with a 30am fuse. Should be able to easily run 10-20 amps through a longer wire run. Then connect the swtiched 12v lead to one side of the coil in the relay, ground the other (85 and 86 IIRC). The relay coil only draws a couple of mA which shouldn't affect the circuit it is connected to.

If one of the aftermarket devices pop...it blows the fuse on the 12 ga wire. The relay electrically isolates the factory wiring from the aftermarket wiring.

You could even use the same relay to power a USB device with the car off like a security camera.

[sapote]

The original circuit is to power the phone at up to 60 watts (14v x 4A), so I feel it’s perfectly safe to power the usb adapter directly without additional relay. Worst can happen is the 5a fuse blows by bad devices or damaged adapter then just correct the problem and replace the fuse.

[cobra]

What other devices are connected to the 5a fuse circuit? Is that fuse in the glove box with all the others?

[sapote]

these are the devices that connected to F7 and all of them are lower power input control interface:

[Bry5on]

Yeah 10W is <1A. I run that fuse/wire directly to my 15W phone charger, the 5A fuse has never popped. If you’re running wires and you want a dedicated fuse, don’t tap in to an existing fused wire, just install a receptacle in an unused fuse location (like fuse 13, used only in cabrios) with whatever size wire and fuse you need.