Xl4015 4~38v to 1.25-36v 5a Dc-dc Adjustable Step-down Power Supply Module// 5a Xl4015 Dc-dc Step Down Adjustable Power Supply Module LED Lithium Charger//5a Dc-dc Adjustable Step-down Module Xl4015 4~38v 96%

The modules are functioning without issue. The output voltage is adjusted by the potentiometer (Blue box with the screw). The number of rotation is larger than the usual variable resistance. If the output voltage does not change, you had better try to turn the screw clockwise or anti-clockwise until it clicks, then check the output voltage. I check the number of screw's rotation and it is around 30 times from maximum position to minimum position.This time, I try to make a simple electrical load with a constant current mode by myself. The architecture is very simple like this: USB Charger(5V)---this module(set to 1.5V)---1ohm/100W resistor. If you would like to set a 1.5A constant current mode, just set the output voltage to 1.5V. That is, it is 1.5V / 1ohm = 1.5A by the ohm's law. You had better use a 1ohm/100W resistor with a heat sink when the output current is 2A or more.

I love trying these China made circuits. I even use them to teach kids about electronics. It is hard not to at the prices. Unfortunately I bought two and neither worked (no voltage control with pot) so warning to any future buyers.