Building "1 port plug and play" 12v system - Page 1
Forum section: electronics / beginners

author: NLG
author_rank: Newbie
timestamp: April 01, 2023, 06:15:55 pm
content: I am trying to build a PS3 super slim (12v, ~65w power consumption) into a laptop form factor, and would really appreciate anyone's help on this, this is the last major thing I need to figure out.My goal is this:One charging port where you plug in a power supply (>65w), and through some circuit/board the power is sent directly to the PS3 system, and any leftover current is used to charge some 18650 cells.When the power is unplugged, the system switches to using the battery for power.This is opposed to a BMS in which the input and output terminals share a common ground.Now, I have two main questions that I could use some help with:0. Does anyone know of a board out there that does this? I found thishttps://www.batteryspace.com/CMB-for-14.8V-Li-Ion-Battery-Pack-10A-limit-RoHS-Compliant-with-DC-char.aspxboard but I want to know of other options. Also open to making my own PCB but I'm a mechanical engineer so I have no idea how to design a circuit like this.1. The PS3 motherboard runs off 12v, so should I use a 3s arrangement and a boost-buck converter OR should I use a 4s battery and a buck/stepdown converter? With a 3s, I may be able to get away with not having any voltage regulator and power the board from 10.6v to 12.6v but I still need to test and see if the ps3 board can handle that.Any help would be GREATLY appreciated!!

author: m k
author_rank: Super Contributor
timestamp: April 06, 2023, 10:46:35 am
content: Quote from: NLG on April 01, 2023, 06:15:55 pmDo you mean that charge and discharge must have a galvanic isolation?

author: paulca
author_rank: Super Contributor
timestamp: April 06, 2023, 11:11:13 am
content: I am making the same thing with slightly different purposes.I am going with more cells for a higher voltage and will be using a 26V supply to charge it.In my case I just want silent battery power at various voltages for audio stuff and the electronics bench supplies.So when it's in use it will disconnect from the charger, galvanically isolate itself from it using a dual pole relay.I will need a 12V output rail too. (I will have others though). For the 12V rail I intend to use a 5A fuse, 3A poly fuse, quiet buck converter, PI filter, linear LDO regulator -> DC Jack.The 6S (in my case) will absolutely be protected by a BMS. Not doing so with the batteries in series is far too dangerous without careful consideration and monitoring. It's not just balance, but fault currents. If you short a lithium battery bad things happened fairly quickly. Similarly if you exceed not too high a voltage on a single cell, bad things can happen. A BMS will protect you. It will also protect you from draining the battery dead which is also "almost always fatal" for the battery or potentially you when you charge it again and it burns your house down while sleeping.The only missing part in my case is how to tell when the system is "in use". For that I can use a current sense resistor on the outputs, monitor those with a tiny MCU and if they all drop under a minimum I can connect the DC input and begin charging the pack. Similar if the box is in use and the battery reaches minimum voltage it will turn the DC input on. If DC input is unavailable the BMS will shut the battery off to protect it before it hits the absolutely 2.5V per cell limit (LFP cells).Why are you concerned with "sharing a ground"? If you DC input is connected there is no ground or anything to share it with. I'd be more concerned about the noise coming in on the HDMI ground than from the disconnected - DC input.