timestopMachinist
Posts: 3
Joined: Thu Feb 07, 2019 12:13 am

battery questions

Sat Aug 10, 2019 6:14 pm

I'm making a portable emulation machine with the pi 4, and im confused about power solutions.
im using this screen

https://www.ebay.com/itm/Dell-LG-Displa ... %7Ciid%3A1

with this controller board

https://www.ebay.com/itm/M-NT68676-2A-H ... %7Ciid%3A1

I realize that it would be difficult to power both with one battery, so i dont mind using more than one. I was going to use a lipo and the adafruit powerboost 1000 to power the pi, but am rethinking this due to lipo safety concerns. It seems like li ion might be the best option to power the screen, and if that seems to be cost effective enough, i see no reason not to also use this for the pi. I dont really know how i would go about setting up li lion batteries, or where to get them for the best price, or even everything i would need really, so advice is appreciated. space is not really a concern, as while i do intend my build to be portable, the case i have is very large.

drgeoff
Posts: 9808
Joined: Wed Jan 25, 2012 6:39 pm

Re: battery questions

Sat Aug 10, 2019 6:22 pm

The Powerboost 1000 is not really up to the demands of a RPi4B.

timestopMachinist
Posts: 3
Joined: Thu Feb 07, 2019 12:13 am

Re: battery questions

Sat Aug 10, 2019 6:28 pm

drgeoff wrote:
Sat Aug 10, 2019 6:22 pm
The Powerboost 1000 is not really up to the demands of a RPi4B.
Do you know of a better alternative?

wh7qq
Posts: 1326
Joined: Thu Oct 09, 2014 2:50 am

Re: battery questions

Sat Aug 10, 2019 7:13 pm

There are some questions that need answers before you start, especially, how long you intend to have it operating on battery power before recharging. For some reason, your first link does not respond for me so I can't speak to the display but the controller board will require 12 volts at an idle power of 0.5 watts. The RPi 4 has a recommended power requirement of 5V at 2.5 amps but I have heard of them drawing much less power. so the range is wide but the voltage requirement is strict and the "official" supply is spec'd for an average user's power consumption with some headroom. It will require a REGULATED 5V for the RPi. In any case, you must provide for at least two voltage levels and depending on the display, possibly more.

LiPo's are safe enough as long as you adhere to the charging/discharging requirements strictly and prevent overheating. It is best to go with the more conservative ratings on these cells and also to avoid the super-compressed form factors used in some smart-phones. They have a nominal voltage of 3.7 V but fully charged are up to 4.2. Full discharge is at around 3.2 V. Charge rate recommendations are all over the map but I tend not to believe the higher claims of some. Panasonic is a pretty good reference for conservative ratings on their various cell models. Other outfits may actually put their own packaging on cheaper cells and give outrageous numbers for charge/discharge/rate ratings. The display requirement for 12V means either a stack of cells or a boost regulator, or a 12 V battery.

You need to decide your runtime needs and the current requirements at each voltage level along with the weight and size requirements you may impose on the system. Add 10-20% at least for headroom. Then you can make a decision on battery/regulator(s) if any/charging methods, etc.

My basic advice is to go with one of the larger RPi HDMI displays and use separate supplies for the RPi and display (with a common ground)...forget the bigger display and controller.

As for the Adafruit 1000C...fine product if your current requirement does not exceed 1 amp but the RPi4 will require twice or more that current. As for larger boost regulators, you are on your own here but a good search engine is your best bet for info. Again, discount wild claims of current capacity, etc.

W. H. Heydt
Posts: 10886
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: battery questions

Sat Aug 10, 2019 8:09 pm

wh7qq wrote:
Sat Aug 10, 2019 7:13 pm
The RPi 4 has a recommended power requirement of 5V at 2.5 amps...
The recommended power for a Pi4B is 3A. 2.5A (the spec for the Pi3B/Pi3B+) is expected to be adequate for most uses. The previous RPF PSU was rated at 2.5A and the RPT has made a very inexpensive micro-USB-B to USB-C adapter available so that one can use the previous generation of PSU.

The 3A rating allows the Pi4B to provide 1.2A to USB ports. This implies that a Pi4B running flat out with GPIO pins, HDMI and Ethernet jack being fully powered may need 1.8A.

My general advice to anyone wanting to use battery power is to convert all power requirements to Watts and all capacities to Watt-hours. It makes the relevant calculations much easier. Be sure to allow for conversion losses. Be conservative.

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