Water cannon, 12V 60W step down to 5V for Pi + AI hat +

Hi

I’ve built a watercannon that squirts water at my chickens to shoo them off my deck/verandah.

watercannon/README.md at main · lukerohde/watercannon · GitHub. See feature/hailo for the hailo code (it was tricky to adapt)

Anyway, before I solder and package it up, I’d really like to run all the power off a single 12V 60W adapter. I am struggling to prevent the pi from shutting down due to under voltage. I think I need to get a bigger step-down buck converter than DC-DC Multi-output Buck Converter (3.3V/5V/9V/12V) | Buy in Australia | DFR1015 | Core Electronics. Any ideas?

From the 5V side I’m trying to power a Raspberry pi 5 under hi load, the AI Hat plus servos via PCA9685 servo controller. On the 12V input side I also have solenoid. I think this is coming close to 20W - theoretically that buck converter should handle it, but theoretically my 25W power supply should been ok too. I bumped up the DC power adapter to 60W and everything was working good until I got the AI hat. The Buck convert really whines high pitched now, and perhaps it can run for about 30 seconds before the pi conks out due to low voltage.

I tried getting the 75W step down. DC-DC Adjustable Step-down Module 5A 75W | Buy in Australia | CE07271 | Core Electronics. The one I got is faulty, so I didn’t get to test it, but its max output is still only 5A i.e. 25W, so it may not work. Any suggestions?

FWIW here’s a description of my schematics.

On my breadboard’s left power rail, I have the 12V input, this rail also powers my solenoid (which is controlled by an optically isolated relay, and also has a flyback diode).

Between the two power rails I have a 12V to 5V step down buck converter, and a common negative between the 12v and 5v.

On the right rail I have my servo controller, a big capacitor to smooth things out, common negative to the pi 5. And a female USB+C connector, that I really want to power the pi with.

The pi5 has gpio17 to relay for the servo, and signal power to the relay and server controller. It also has the SDC and SDL controls going to the server controller.

Thanks in advance.

Hi @Luke279165

Welcome to the forum!

Given the power requirements of the Pi5 (5V @ 5A) it is recommended to power it via USB C with a PD capable power supply. While the Pi will work with at currents under 5A you will get reduced performance and the ability to power peripherals will be greatly reduced.

If you’re wanting to power it with the current supply that you have I would recommend looking at Grove - Vision AI Module V2 and the pre-compiled Chicken Detection Model as it will be far far far less power hungry than a Pi.

Hi Luke
Be aware that that 75W buck converter has 2 adjustments, Voltage and Current limit. Both these adjustments are multi turn pots and could be 20 turn types. So you may have to turn it quite a few turns to see anything happening. If this device is limiting at 5A (25W) the way it will do this is to reduce the voltage so the load draws 5A. This could be why the Pi is stopping due to low voltage.
Cheers Bob