Reddit mentions of Gowoops 5PCS 150W DC-DC 10-32V to 12-35V Step Up Boost Converter Module Adjustable Power Voltage

I've done this before. The trick is finding a slim monitor with an external power supply as mentioned already. The ones I've come across run on 19v.

Then it's as simple as wiring up a step up converter and adjusting it to 19v out.

Here's the one I used
https://www.amazon.com/dp/B01GRIQBRY/ref=cm_sw_r_cp_apa_dGcYBbWS76NDN


That said it's also really easy to buy a small $20 inverter and not have to deal with all that

Step 1: Understand how voltage, current, and power draw work. You clearly don't at the moment.

Step 2: You could try something like this, it at least claims to have the oomph you're after.

https://smile.amazon.com/Gowoops-10-32V-Converter-Adjustable-Voltage/dp/B01GRIQBRY

So, something like these?

https://www.amazon.com/Gowoops-10-32V-Converter-Adjustable-Voltage/dp/B01GRIQBRY/ref=mp_s_a_1_5?keywords=12v+boost+converter&qid=1551120922&s=gateway&sr=8-5

https://www.amazon.com/DaFuRui-Converter-Regulator-Convert-Phones、MP3、MP4/dp/B07KGNHGLW/ref=mp_s_a_1_2_sspa?crid=1UWDKIKAGLKTE&keywords=5v+boost+converter&qid=1551120878&s=gateway&sprefix=5v+boos&sr=8-2-spons&psc=1

And these for the batteries?

https://www.amazon.com/EBL-lithium-Rechargeable-Batteries-Upgraded/dp/B0129F9BXK/ref=mp_s_a_1_5?adgrpid=55675675603&hvadid=274750007929&hvdev=m&hvlocphy=9011555&hvnetw=g&hvpos=1t1&hvqmt=e&hvrand=14665574995411272658&hvtargid=kwd-295887349086&keywords=18650+batteries&qid=1551120821&s=gateway&sr=8-5&tag=hydsma-20

Also, when I'm wiring everything up do I want to connect the batteries together and then wire the boost converters to to combined output of the batteries, or should I use one battery for the 12v converter and one for the 5v converter?

Thanks for the reply! You've been very helpful

Searching around on Amazon, I found this.

Would this fit my need? My understanding is that it would take the 12V input and boost it to whatever voltage I set it to, say 19V. And the current through the converter would just vary depending on how much power my system is drawing, correct?

Thanks for the help

Oh OK, I never would've thought about charging it while its off until after I had already glued everything together lol.

I went ahead and tried both ways you've just mentioned here to see how it works as I don't have a relay (I'm probably going to end up buying it anyways when I'm done with this prototype and build the real thing).

I bought these adjustable boost converters:

https://www.amazon.com/Gowoops-Converter-Voltage-Adjustable-Circuit/dp/B01GRIQBRY/ref=cm_cr_arp_d_product_top?ie=UTF8

They take input from 3-30V and output to 4-35V and seemed to be perfect, but when I set everything up like your diagram above, everything actually runs fine with no low voltage but the boost converter makes some interference on the screen.

Ive tried grounding the screen directly to the Pi, the powerboost and its own boost converter, but its ever present when powered by this adjustable boost converter. The screen shows no interference when powered from its own wall charger while the Pi powered from the battery. Also no interference when the screen was powered directly from the Pi when it was doing the low voltage thing.

I see on google that EMI notorious with boost converters, did you have this problem with your old set up? Do you think it could be because its a cheap adjustable one?

Also when I wire the boost converter after the powerboost, to try to give the Pi 5.2-5.4 volts but the raspberry Pi just keeps rebooting over and over. Ive checked its output voltage with the multimeter in that setup and its within the Pi 3's voltage range but it never gets past the emulationstation loading image.

The screen interference is not so bad that I cant live with it, still definitely playable, but if I can fix it I want to.

Again thanks for your help

EDIT: So I basically took your diagram above and swapped the boost converter and the powerboost around and it works perfect! The Pi doesnt seem to mind the interference from the cheap boost converter and the screen works perfect with the powerboost! This leaves the Raspberry Pi being powered by a cheap $2.40 adjustable converter and the $15 screen powered by the $28 powerboost, but it works!