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RPi power supply

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DaOld Man:
I have a 10" touchscreen monitor for my RPi jukebox project.
The monitor currently has a 12 volt power supply, and the monitor's circuit board has a buck circuit to output 5 VDC to power the RPi.
I wish to power off the monitor when the RPi shutdowns, because the monitors back light stays on when RPi is shutdown.
Now I can use two power supplies, the 12 volt for the screen and a 5 volt for the RPi, then shut off the 12 volts when the RPi shuts down. (Via relay powered by RPi's usb port).
But that means more room (2 power supplies).
Has anyone played around with a buck power converter (available on amazon and ebay), to convert 12 volt to 5 volt?
I could power the screen and the buck converter with one 12 volt wall wart.
Looks to me like the converter will have to be able to supply at least 3 amps for the RPi. (RPi 3 b)
I was wondering what the current is on the 12 volts with the screen sucking on it and the buck (powering the RPi)?
The current 12 volt wall wart that came with the screen is rated at 1.5 amp.
I did get a few under volt alarms on the RPi while being powered from the monitor, so Im thinking I will need a bigger 12 volt supply.

nitrogen_widget:
Yeah, you will need a bigger 12v supply. 6a should do it. Plus its a common v/a psu.
on those buck converters, they list 3a max output so actual output is probably a little lower.
they should probably be enough if you are just playing music and just using the screen for the interface.

one important thing though is you want to use a micro usb connector to come off that buck converter to power the pi as there is zero protection when connecting power to the gpio pins.

DaOld Man:
Thanks Nitrogen_widget!
Yeah, I will be playing music AND using the screen as a touch interface, so maybe I need to design the cabinet to allow room for both PSU (wallwarts).
I would love to use an arcade power supply for both 5 and 12 volts, but they take up a lot of room.

nitrogen_widget:
would this fit?
6.2x3.8x1.5 inches.
has 12 and 5 volt also.
https://www.amazon.com/Arcity-Switching-Adjustable-Machine-Cocktail/dp/B07X1LBK19/ref=sr_1_5?crid=1PFRVIE8AAA5N&dchild=1&keywords=arcade+power+supply&qid=1618600200&sprefix=arcade+power%2Caps%2C200&sr=8-5

DaOld Man:

--- Quote from: nitrogen_widget on April 16, 2021, 03:14:46 pm ---would this fit?
6.2x3.8x1.5 inches.
....

--- End quote ---

Thanks! It might. Since I havent really started on the cabinet yet I can "build around it". I was trying to keep it as small as possible, but that PS might work.
I will have to cut out a cardboard template and scratch my head a bit.

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