Reefpi - Help with LM2596 Buck Converter

jayscoobs · Jul 12, 2020

Hello! Not sure this is the right place to post this. Disclaimer I am not good with electronics but I decided to take on a reef-pi project. My background is in IT but never worked with anything electrical unless you count UPS in server rooms.

I am following the adafruit power controller guide and I am stuck on trying to tune the LM2596. I am trying to use the power supply that I have with the barrel jack connector to power the LM2596 so I can step it down before connecting to the protohat.
The problem I have is the power supply won't power on the converter. DCV testing with multimeter shows that I get 12V at the barrel jack connector as well as the leads. But when I connect the leads to input + and - on the LM2596 I get almost 0 volts at the barrel jack connector and at the leads. It is like the power supply stops working once the converter is connected.

Any help appreciated. Even if there is a different or better way to do this. Heres the adafruit guide.
https://learn.adafruit.com/reef-pi-power-controller/hardware-setup

Michael Lane · Jul 12, 2020

Welcome to Reef2Reef!

It sounds like you've taken the right steps so far. It may be helpful if you post some clear pictures of what you have. In the meantime, here are some ideas.

1. Bad wiring - Double check all wiring. Try to isolate this from other parts of the circuit if more is built. Post some pictures.
2. Bad settings - Does anything change when you turn the trimmer screw? Is there anything on the output of the module? You may need a minimum load for it to start regulating. Try connecting an LED and 100 - 1000 ohm resistor to see if that changes anything.
3. Bad module - Do you have another you could swap in? Does a visual inspection reveal any soot marks or bad solder connections? It can be possible to troubleshoot and repair if it's a bad module, but these are usually better to just replace since these so cheap.
4. Bad testing - It sounds like you know how to use the voltmeter, but I'm trying to brainstorm everything that could be wrong.

Ranjib · Jul 12, 2020

jayscoobs said:
Hello! Not sure this is the right place to post this. Disclaimer I am not good with electronics but I decided to take on a reef-pi project. My background is in IT but never worked with anything electrical unless you count UPS in server rooms.

I am following the adafruit power controller guide and I am stuck on trying to tune the LM2596. I am trying to use the power supply that I have with the barrel jack connector to power the LM2596 so I can step it down before connecting to the protohat.
The problem I have is the power supply won't power on the converter. DCV testing with multimeter shows that I get 12V at the barrel jack connector as well as the leads. But when I connect the leads to input + and - on the LM2596 I get almost 0 volts at the barrel jack connector and at the leads. It is like the power supply stops working once the converter is connected.

Any help appreciated. Even if there is a different or better way to do this. Heres the adafruit guide.
https://learn.adafruit.com/reef-pi-power-controller/hardware-setup

Welcome to r2r. As Michael mentioned, this sounds like a wiring or bad component issue. Can you share a photo of your test setup ?

jayscoobs · Jul 12, 2020

Hi Guys, Appreciate the help so far! Here is a few pics in imgur with descriptions.

I have tested with both modules I got on Amazon with the same result with both. A voltmeter on the output end shows I am getting the same .60 DCV and no change when moving the screw. I'd expect it could be a power issue since I am not getting the screen to light up on the module either.

Ranjib · Jul 12, 2020

jayscoobs said:
Hi Guys, Appreciate the help so far! Here is a few pics in imgur with descriptions.

I have tested with both modules I got on Amazon with the same result with both. A voltmeter on the output end shows I am getting the same .60 DCV and no change when moving the screw. I'd expect it could be a power issue since I am not getting the screen to light up on the module either.

On the power connector end, can you take voltage reading of all combination of pins? Like one 1-3 as well as 2-3 , and does the voltage reading changes to negative when you flip the pins ?
What’s the voltage reading on the lm2596 screw terminals? Check both combination

Ranjib · Jul 12, 2020

jayscoobs said:
Hi Guys, Appreciate the help so far! Here is a few pics in imgur with descriptions.

I have tested with both modules I got on Amazon with the same result with both. A voltmeter on the output end shows I am getting the same .60 DCV and no change when moving the screw. I'd expect it could be a power issue since I am not getting the screen to light up on the module either.

The adjustment screw had to be turned few times before you notice the effect in output voltage . But for me , the starting output was 11v (I think there’s 1v minimum drop ) , which does not tally with your observation :-(

Ranjib · Jul 12, 2020

Edit: Posted by mistake, this was not relevant to this thread.

Michael Lane · Jul 12, 2020

That's strange. It looks like it measures 12v on the supply when disconnected, but 0.6v when connected to the converter.

That either means the modules are defective, or the power supply is defective.

Spieg · Jul 12, 2020

Agree, it seems like something is not wired correctly, or there is a defective part. Is the buck converter resting on anything conductive that might be shorting a circuit?
FWIW - I don't like the 3 post barrel jacks... you only need 2 posts and the third just adds potential to wire it wrong. I use one of these with only two posts;

Also I like the converters with onboard voltmeter (so convenient press one button to display voltage in and the other button to display voltage out);

oreo54 · Jul 12, 2020

jayscoobs said:
Hello! Not sure this is the right place to post this. Disclaimer I am not good with electronics but I decided to take on a reef-pi project. My background is in IT but never worked with anything electrical unless you count UPS in server rooms.

going with the odds.. bad power supply...
Got a different one ?

jayscoobs · Jul 13, 2020

Tested both modules and this is what I get checking Ohms on both of the input pins.

I also use the one with the built in voltmeter. Display should light up at 4V. I took this PSU from my old TP-link modem as it seemed to be the same specs as the adafruit one. I have a 24V adapter from my old wavepump that fits which I did with the same result.

I'm at a loss as it doesn't make sense why it shouldn't work to me. Both PSU's give me Voltage on my DMM but once modules are connected it goes caput. I do have a breadboard, 470ohm resistors and LED's. Maybe I can create a circuit with that to see if it will power it? Or try the 2 prong barrel jack or another LM2596?

jayscoobs · Jul 13, 2020

Garden looks good by the way! I'm still in an apartment so I don't have much plants lol. Here's my tank though. I need a better way to take pics. Got that Jack o'lantern leptoceria for 25. Also got a pistol and a goby combo recently but my dwarf pygmy angel didn't like the goby and killed him right away =(. Probably due to size of the tank. Reefpi is future proof for when I go bigger and get a in cabinet sump.