USB switch for 12 volt car cigarette lighter?

Thread Starter

ari101

Joined Jan 13, 2022
6
The 12V outlet in my Mazda3 is "hot" even when the car is off. The USB ports next to it only have juice when the car is on. Is there an existing device or can something be built that would deactivate the 12V outlet when the USB port no longer has power? I'm imagining a male-to-female 12V plug with a USB port on it.

Thank you
Ari
 

Rich2

Joined Mar 3, 2014
241
I made a timer so the accessory socket goes off about 1 hour 10 minutes after the ignition. It's useful if you want to charge something, but still goes off.
 

MisterBill2

Joined Jan 23, 2018
11,579
Why not just use the switched accessory feed for the lighter socket? That line should be accessible on the fuse block. In my car the change can be made by altering the position of a fuse, to allow either switched or constant feed.
Certaainly it is worth the effort of examining the fuse block.
 

Externet

Joined Nov 29, 2005
1,817
I do not understand why to turn off the 12V outlet. I did the opposite for my vehicle by powering the 12V outlet permanently from an added fuse to battery, to be able to charge something with the vehicle parked.

Perhaps one of these can serve you better. There is switched, unswitched, multiple, single, but installing a USB switch to turn off may not be wise. A USB switch may not be capable to conduct the current needed out by that outlet.
If a usb adapter for the lighter outlet stays on, just pull it a few millimeters out.

----> https://www.ecosia.org/images?q=usb outlet 12v car

1642168843632.png
 

Rich2

Joined Mar 3, 2014
241
The reason I made mine turn off is sooner or later I'll forget something is plugged in and will find a flat car battery. It's only a 40ah battery and I used to have a little DAB+ radio adapter plugged in.
 

MisterBill2

Joined Jan 23, 2018
11,579
Nothing back from the TS yet. I had an older (1976) Dodge van and sometimes I would forget and leave the CB radio on when I parked it. Then three weeks later when I went to use it again the radio would greet me with chatter when I opened the door. So if the battery would run flat in just a few hour then there is either a battery problem or a charging system problem. OR a very high powered accessory plugged in. An inverter powering a computer and a monitor?
 

Tonyr1084

Joined Sep 24, 2015
6,863
The 12V outlet in my Mazda3 is "hot" even when the car is off.
What year is it? If it's an older model, back in my young days (yes they had cars way back then) the cigarette lighter was always powered, and it was for lighting cigarettes. That's why it's called a cigarette lighter.

If you want to have the outlet off when the key is off then you'll need to find a suitable circuit to power it when the key is on. The USB port is likely good for 5V @ 2A. That's 10 watts. 10 watts at 12 volts would be good for no more than 833mA (0.8 amps). That's not going to be useful for anything practical.

Ramussons suggests using a 5 volt relay to control the power to the 12V outlet. That's one way to approach it. A 5V usb port can supply sufficient current for a small relay who's coil is rated for 5 volts, and the relay should be rated for something equal or greater than the fuse that the 12V outlet is connected to. If memory serves me - back then cigarette lighters were on either a 15 or 20 amp fuse. And the associated wiring was rated to handle that much current. In today's modern cars they don't seem to put larger than 10 amp fuses on those outlets. That means the wiring isn't going to be able to handle more than 10 amps. At least I wouldn't ask it to.

So what year is your Mazda?
 

Tonyr1084

Joined Sep 24, 2015
6,863
I had an older (1976) Dodge van and sometimes I would forget and leave the CB radio on when I parked it.
72 Chevy Nova. And yeah, I've been there too. I don't recall finding a dead battery either.

Mine had a high compression engine. The battery needed to be strong to turn the engine over. If it was just a little flat then it would act like a dead battery. One evening I was stuck and couldn't find a jump from anyone. The wife was with me. I took a pair of needle nose pliers and shorted the ignition coil while she cranked the engine. After just a few revs I'd let the spark hit and the engine would always start. After that I added a kill switch I could use in the same manor. However, today's cars are being built lighter, which means smaller batteries with less capacity. I believe that has a lot to do with fuel mileage requirements. That along with smaller gauge wiring, all in an effort to reduce the weight of the vehicle. I would suspect that a device left plugged into the outlet could easily drain a battery over night. Hence, the request to be able to shut the outlet off when the key is off. However, I, too, have wished I had a live outlet so that I could plug a phone in and let it charge. Suppose there's a power failure and I have no way to charge my phone except to run the car engine. Pretty expensive five volts. No? It so happens that I have two spare car batteries in my garage. One's duty is to power a car radio, and it is kept on a 13.8V trickle charge. The other remains on a battery maintainer from time to time so that it can provide a source of power should there be a need. A cigarette lighter outlet with a short cable and some alligator clips can turn that battery into a convenient source of power.
 

Thread Starter

ari101

Joined Jan 13, 2022
6
Thank you everyone for your responses! I have 2016 Mazda3. I believe the 12V outlet is connected to a 10 amp fuse. @MisterBill2 So I better understand, would this require moving the 12V outlet wires to a different / switched fuse position?
 

MisterBill2

Joined Jan 23, 2018
11,579
It may be that one is switched and one is not. AND, given that the car does not have a 5 volt battery, probably the feed wire to the 5 volt outlet is 12 volts and the regulator is built into the outlet. It often works that way.
Next, how much current do you want to provide for with that lighter outlet? That matters a lot. Powering a coffee maker from a vehicle outlet is one extreme, charging a cell phone with a plug in adapter is the opposite extreme. So what you want to power affects the useful options.
 

MisterBill2

Joined Jan 23, 2018
11,579
Probably the difference will be so slight that you will not notice it. The rating in the manual is the charger's capability, not the phone's requirement. The phone will take what power it needs. To know the rating of the USB outlet in the car you will need to search the owner's manual. And the good news is that you will still have the 12 volt outlet available for whatever ele you may choose to power.
 

Thread Starter

ari101

Joined Jan 13, 2022
6
I will give the USB port a try. If the charging rate is an issue, I'm going to go this route:
and put a socket near the fuse box. Thank you everyone for your time! :)
 

djsfantasi

Joined Apr 11, 2010
8,255
Seems like my 2012 Camry uses LED lights for its cabin lights.

I’ve forgotten to turn them off a couple of times. Normally that would drain the battery overnight. Didn’t happen. My guess is that LEDs don’t draw enough current to drain the battery overnight.
 

Thread Starter

ari101

Joined Jan 13, 2022
6
It’s possible to drain the battery on the Mazda3. I once let my car be used as a phone charging station during a short camping trip. I needed a jump to get home.
 

ThePanMan

Joined Mar 13, 2020
342
Just remembered - - - Here is a hard wiring kit for dash cam's. (note - Web Activity Tracking has been deleted from the link) It can be powered from voltages anywhere from 12 to 24 volts and outputs a steady 5V to a micro-USB plug. It even has a feature that if your battery voltage drops to 11.6V (or 23.2V) it shuts off, preventing the battery from being drained further; and you can still start your car. You can connect it to an "Always ON" circuit or you can connect it to a "Switched" circuit.
 
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