Battery for computer (like laptop battery) - Page 1
Forum section: electronics / projects

author: possum
author_rank: Contributor
timestamp: March 30, 2018, 04:55:39 am
content: I need to design battery for computer. I would prefer to use something off the shelf but could not find anything. Basically, I want something similar to laptop battery pack.What I have now:Computer powered by a standard 19V laptop power brick.Motherboard already accepts 19V as input (Intel NUC or something similar), and not very power hungry.To power up the LCD screen, 19V is also converted into 12V (dc-dc converter, 2A max).Now I need to have a battery backup for both motherboard and LCD screen. Probably 3 or 4 cells in series but I'm open for suggestions. I think I will use these cells: BL-5C or 18650.I could not find any simple solution, maybe I just don't use right keywords.Also would be nice (but not mandatory) if battery pack can communicate with computer just like any standard laptop (show how many charge left, charging/discharging etc.)

author: Jeroen3
author_rank: Super Contributor
timestamp: March 30, 2018, 05:35:47 am
content: Any off the shelf UPS for a $100 will do. Do you have very specific needs that you want to make your own?

author: Chriss
author_rank: Frequent Contributor
timestamp: March 30, 2018, 09:37:14 am
content: Do you want to make a portable backup system maybe?

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 30, 2018, 10:20:39 am
content: not a difficult thing to do, just connect a battery to the pack, some diode to avoid reverse current maybe, or trickle charger when on mains and put in an arduino to voltage monitor and talk to the PC, and you are golden. ps: i have an atom system that runs on 12V adapter pack, so i kinda understand this situation.

author: soubitos
author_rank: Frequent Contributor
timestamp: March 30, 2018, 11:32:49 am
content: There are two way to work around this (to me at least)1. Make a beefy and complex 6S lithium battery pack wich is PITA to manage charge balance etc but at the same time allows for two back converters to generate 12+19V2. Make a 4S battery pack which is more or less easier to handle and have a back converter for the 12V and a boost converter for the 19V rails.I want to finish a 3S setup myself to replace the ATX PSU of my miniITX AM1 PC (max 25-30W) and get an LG monitor i set my eyes onto which works @ 19V/1.8A i think. I have most of the setup ready and initial tests show it will work very well. All electronics and perhaps a smaller 3S3P pack will be installed in the case of an old ATX PSU and there will be connectors to allow for additional packs (3S5P) to be hooked externally in case of a power shortage that lasts a bit longer. Based to very simple estimates a 3S5P pack would keep the setup (PC+Monitor+Router) running for around 2-3hrs... the idea is to have 4-5 packs charging from a rather small solar panel (50W should be good enough) so it could be possible to have the pc working for 15-16hrs a day without mains power.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 30, 2018, 03:13:21 pm
content: I won’t be much help but my Asus PC came with a small UPS inside and after few years it failed and I had to replace it, but before doing so I took it apart and inside were 3 18650 cells unprotected by LG one of them overdischarged so I had to replace all 3 cells.They were connected in series and they could all put out 30Amps, so you can definitely use 18650 but you need to make sure they are those 30Amp ones that Vapers use, I suggest going to their forums they usually have cheaper hookups with the battery selling websites. I would not buy those off eBay or even amazon.

author: Dr. Photon
author_rank: Contributor
timestamp: March 30, 2018, 09:34:22 pm
content: Perhaps an "OpenUPS" from mini-box? I have not used one of these before, but I did use one of their 12VDC powered ATX power supplies for an old carPC projecthttp://www.mini-box.com/OpenUPS2?sc=8&category=981

author: Nauris
author_rank: Regular Contributor
timestamp: March 31, 2018, 07:23:28 am
content: NUC runs on 12V too. Just get a lead-acid battery and a 13.6 V power supply for your computer.

author: David Hess
author_rank: Super Contributor
timestamp: March 31, 2018, 04:34:41 pm
content: Check the actual input voltage range of your NUC or NUC clone. If it will accept 12 volts, then use a pair of isolation diodes, a standard 12 volt sealed lead acid battery like Nauris suggests, and a 12 volt sealed lead acid battery charger. Or buy one of thoseBelkin 12 volt battery back up power supplies; they can be found on Ebay for cheap because cable and DSL companies were including them with their battery backed up CPEs which included phone service.If you just want to buy something, then the OpenUPS2 suggested by Dr. Photon might work.

author: rx8pilot
author_rank: Super Contributor
timestamp: March 31, 2018, 05:14:22 pm
content: I just made a system like this for NUC's. They will indeed be fine on 12v. My second iteration runs at 19v and the backup is provided by a 2S LiFe pack (only needs a minute of backup to gracefully shut down)For my application, I was unable to find anything off the shelf, but I had some overly specific needs.A couple of ideal diodes and 13ish volt battery would be pretty simple.Short and misplld from my mobile......

author: mariush
author_rank: Super Contributor
timestamp: March 31, 2018, 06:00:32 pm
content: A single 12v lead acid battery, a dc-dc boost circuit to boost 10..14v to 19v , maybe some low drop linear regulator for the 12v for monitor (because your battery may be up to 13-14v when fully charged)or ..Two 12v lead acid (maybe crystal for deeper discharge and resistance to being damaged when discharged too much) batteries or a single 24v battery, a DC-DC converter to produce 19v from 20 .. 26v (though your NUC will probably work with 18.5v or even 16v, but the efficiency of the VRMs may change)The charger could be a simple 120v / 230v -> 24v AC transformer, a bridge rectifier and a linear regulator to charge the battery with around 26-28v

author: rx8pilot
author_rank: Super Contributor
timestamp: March 31, 2018, 08:00:41 pm
content: I have been successfully powering 10 NUC's at 12V for 6 months. They run slightly warmer, but not enough to cause much concern.Not sure what under voltage threshold they have.....12v may not offer much wiggle room. Ultimately I designed a boost/buck converter that outputs 19V. It either runs from a single 12v nominal battery (11-17v) or two of them in series (22-34v which means the converter is never in the boost-buck region.For reference:Average current for an i7 NUC at max power is under 3A @19v- it has brief peaks up to around 4A or so. Idle can average around 1A @ 19vIf you have primary power 19v and a diode OR'd 12V battery - that will create a simple and reliable backup system.

author: possum
author_rank: Contributor
timestamp: April 25, 2018, 04:49:58 am
content: No lead acid battery - too big and heavy.OpenUPS mentioned above is probably what I need, however the price is ...I'm looking for something with bom cost (excluding cells) under $20 ideally, which works just like laptop battery pack.But I could not find any simple one chip solutions. Looks like everyone use some micro with custom code to control the charging and communication with the computer.

author: possum
author_rank: Contributor
timestamp: April 25, 2018, 04:52:45 am
content: Quote from: rx8pilot on March 31, 2018, 05:14:22 pmSo, what did you do? How do you charge the cells?

author: rx8pilot
author_rank: Super Contributor
timestamp: April 25, 2018, 05:14:16 am
content: Quote from: possum on April 25, 2018, 04:52:45 amI spent about a month desiging and testing a citcuit that manages the backup battery, primary and secondary power inputs. This required a custom boost converter as well. I don't think the BOM is under $20.

author: possum
author_rank: Contributor
timestamp: May 20, 2018, 05:00:24 am
content: I think I found something.BQ24721C - Smart Battery Charger with SMBushttp://www.ti.com/product/bq24721c