Advice on potentiometer or resistor for power board

I recently ordered a batch of small buck converters that take 12v-24v dc input and drop it down to 9v, 7v, 5v, 3v, etc using a pot.

The product on Amazon is “ eBoot Mini MP1584EN DC-DC Buck Converter Adjustable Power Supply Module 24V to 12V 9V 5V 3V (12 Pack)”.

These were going to be used to power a bunch of NodeMCU modules. Unfortunately, all 12 of the buck converters are missing their pots, so there is no way to use them. I requested a refund, and Amazon did provide it, but they also told me it was a waste of their time to send them back and I could just keep them. I’ve ordered replacements, from a different manufacturer, but I am wondering if I can just solder in a small resistor where the pot should have been? Or order a dozen surface solder pots and solder them in.

But…I don’t know what the resistance of the missing pots is, so I don’t know what to order.

I’ve attached a pic of the buck converter as it should have been, and a pic of what I got (you can see the missing pot solder pads…

If I wanted to just make these either 3.3v output or 5.0v output (or 7.0v, or 9.0v), what resistor would I solder in? I don’t know enough (obviously) about electronics to understand the markings on the pot that is shown, or what resistors to use to achieve 3.3v or 5.0v or 7.0v output on these buck converters.

I hate to throw them away when it seems like I could do a little soldering and get working buck converters. Any ideas?

26-11-20.pdf (1.91 MB)

The picture( you should post the picture directly to the forum) shows two of the three legs of the pot are connected together, so the POT is acting like a variable resistor, not a potentiometer. You can use a fixed resistor to do what you want, but you can't know the value.

Solder two wires to the pads on the board. Use a 10k pot to test with. Solder jumper between the slider pin on your POT and one for the end pins, so it matches the board trace.

The wire soldered to the board trace that shorts the two pot pins needs to be soldered to the shorted pins on your POT. The remaining wire connects to your POT slider terminal.

Test your board using your DVM to see if turning the POT changes the voltage. If it does, set the POT to the voltage you want. Turn everything off, unsolder one wire from the POT and measure the resistance. That is the value of the fixed resistor to use to get the voltage you want.

Good luck!

Makes sense, I’ll give it a try...I can always use a bunch or 3.3v or 5v or 7v buck power supplies. I live completely off grid and my solar system is a simple 12v nominal system, so having these unit able to take in 12vdc-16vdc and spit out a good power feed for NodeMCUs or Arduinos would be a good thing... can go to the MPS datasheet for the part:

Look for the formula under "APPLICATION INFORMATION / COMPONENT SELECTION / Setting the Output Voltage."

Good luck!