Battery power for Raspberry Pi 3B+ with a Waveshare 3.5inch LCD

[Jason193805]

Hi all!
New to the Pi space. I’ve done a lot of research, but figured I’d reach out to the community for a few questions.

I’m trying to figure out how to power a Raspberry Pi 3B+ with a Waveshare 3.5inch LCD by battery.
Ideally something compact.

I’m also trying to find the draw of the LCD but having trouble locating the specs.

I read that RPi 3+ board is protected by a special fuse which permits no more than 2.6A. Is this correct for the 3B+?
Would I be correct in saying 2.6A is the absolute maximum I can run through a 3B+; so as long as I meet that the screen will have plenty of power?

The project in short, I want to use the Pi to store an offline version of Wikipedia (using Micro SD to store the 100GB) and be a nice little compact standalone unit.

Any guidance would be great!

[Jason193805]

I’m thinking something like this:
https://core-electronics.com.au/20w-adjustable-dc-dc-buck-converter-with-digital-display.html
set to 5.3 volts

with:

Rechargeable NiMH Battery Pack: 6.0 V, 2200 mAh, 5x1 AA Cells, JR Connector

Similar to this guide:

Pi 3B+ 3.5" LCD - Battery powered

After getting the Pi 3B+ and 3.5" LCD display to work nicely, I ventured down the path of battery power, so the Pi could shake the shackles of the Plug Pack. The Pi and LCD running draws about 500mA. Conclusions: The Pi Foundation made a big mistake powering the Pi 3B+ via a Micro USB connector. Most Micro USB cables will cause too much voltage drop as the wires are too small. Buying a 5V supply with a higher current level will not solve the situation unless the supply is rated at some very h…

[Liam]

Hi Jason,

Welcome!
Awesome, we love seeing other members of the forums projects being used! And your project sounds very neat!

I managed to track down a comment on the FAQ suggesting it uses 150 mA @ 5 V, for calculations I’d leave a bit of wiggle room.

The onboard fuse will come into play when trying to draw a lot of current through the Pi, to make sure that doesnt happen you could power your other devices through their own voltage inputs but for say a display, and some basic USB peripherals you’ll be all good! I’m wasn’t able to track down a definitive answer for the fuses max current (these resettable polyfuses dont have the same characteristics as a glass or blade fuse that I’m used to)
Below is a photo of the polyfuse on the Pi 3B+'s schematic

Full schematic

Another suggestion for a power supply: the PiJuice:

PiJuice HAT - A Portable Power Platform For Every Raspberry Pi

Its a tried and tested device and uses very little GPIO and offers some feedback to the Pi! PiJuice at Raspberry Pi GPIO Pinout

I’m keen to see how you go!
Liam.

[Jason193805]

Thanks very much!
I was looking at the PiJuice but wanted a more budget friendly option for this project (and a bit more DIY fun). I’ll be looking into getting a PiJuice for other projects though.
Budget is a big consideration as I want to be able to replicate this system and potentially provide devices to people in communities that don’t have access to wiki or other educational resources.

Is the 20W Adjustable DC-DC Buck Converter with Digital Display and Rechargeable NiMH Battery Pack: 6.0 V, 2200 mAh, 5x1 AA Cells, JR Connector combination suitable?

I’m also trying to figure out how best to connect everything. I’m guessing I’d have to wire in a connector for the battery to the Buck converter, and I’m then thinking of connecting a 5v barrel jack out of the converter to go to the pi?