I have an illuminated 2 port usb charger that plugs into a cigarette lighter/accessory socket in a car. The face of the charger is flat and sits flush when inserted into the cigarette lighter/accessory socket. I’d like to install this “permanently” in the rear passanger area of a car so that two passangers can charger their devices. I did not want to install a second accessory socket so I’ve opened the charger and now have the internal circuitry to which I can connect my own wiring.

Since it is illuminated, and since I don’t always have passangers in the rear, like to be able to control this with a switch. Here are the specs for the devices involved:

Power supply from car: 12v, 5A or 10A max from fuse box are both available (switched power)

Switch: 5 pin (NO, NC, C, +, -), max 3A

USB charger:

• Input 10-16VDC 2.9A

• Output 5v, 2.4A max X 2 ports = 5v, 4.8A if both are used at the same time.

QUESTION: It appears the switch I have will not be able to handle current draw if both ports are being used at their max draw (2.4A x 2 = 4.8A). Is this statement correct?

If I still want to use this switch, I will need a relay that can handle up to 5A. Is this statement correct?

Lastly, is it even worth doing all this? Should I just connect the charger directly to power from my fuse box on the 5A circuit with a 5A fuse?enter image description here


1 Answer 1


The photo has more surroundings than the plug itself so it is hard to tell. But based on the huge inductor, most likely that is a switch mode power supply, not a linear regulator, so if it can deliver 24 Watts of power on output, it will take a bit more than 24 Watts power on input, and so it will only draw a bit more than 2A of 12V from car. (If it were linear supply, it would have to dissipate 33W so it would just melt).

  • \$\begingroup\$ Ok, so what does that mean for my question? What is the best way to power this safely so that I can power both outs (5v, 2.4A each)? \$\endgroup\$
    – Inked_xx
    Commented Dec 20, 2018 at 19:09

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