Multi-purpose variable voltage DC power supply for cars

Intended use: charging laptops and smartphones in cars, for example, at a campsite without an electricity hook-up.

Features:

USB PD 18W

QC 3.0

Low input voltage (car battery) alarm

Variable DC output

Left slot: USB PD and QC 3.0 charging ports
Middle slot: Voltage meter for the DC port on the right slot
Right slot: DC output port

For the DC output, I used a SEPIC converter module, which purchased on ebay. This converter module provides 5A output currents with 1V-30V voltage range.

To avoid over-draining the car battery, a low battery alarm module from aliexpress has also been added.

On the back, there are vent holes for cooling, power switch, and voltage adjusting knob.