12V and 5v(USB) battery pack build. help. - Page 1
Forum section: electronics / projects

author: Pexy13
author_rank: Regular Contributor
timestamp: June 13, 2019, 10:34:53 am
content: Greetings!My brother asked me if I could build him a battery pack with 18650 cells that he got from work.He wants a 12V output and a 5V usb output. There are 8 cells in total.I was thinking of doing something in these lines:1) Connect 2 batteries in parallel and then 4 pairs in series.2) Get a 4S BMS for charging.-something like this:https://www.ebay.com/itm/3-4S-BMS-PCB-40A-Li-ion-Lithium-Battery-Charging-Protector-Board-18650-Module/253624191159?hash=item3b0d2e08b7%3Am%3AmfmyTfdOFEIrRDk_IhsnsxQ&frcectupt=true&fbclid=IwAR09bEndrc7S-h7QbTzAPwEeS2zlA6ZarHvIYWIaxgtcFvGB5SzJxzp1l4cor this:https://www.ebay.com/itm/3S-4S-5S-3-7V-Polymer-Lithium-Battery-PCB-BMS-Protection-Board-Balance-Charging/332718178699?hash=item4d778c818b:m:mU0FwbeSu6Qs1LoApTvfXxA&frcectupt=true3) Use a 12V and a 5V regulators on the output of the BMS to have a regulated 12V and 5V USB outputs.- something like this for the 5V:https://www.ebay.com/itm/USB-Charger-12V-24V-8-35V-to-5V-8A-DC-DC-Buck-Step-Down-Power-Supply-Converter/202518994580?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D58654%26meid%3Dee3b6b3e02cf40b59563f36bbdaa12cc%26pid%3D100005%26rk%3D5%26rkt%3D6%26mehot%3Dag%26sd%3D381374423467%26itm%3D202518994580&_trksid=p2047675.c100005.m1851- something like one of these for 12V:https://www.ebay.com/itm/XL4016-DC-CC-8A-200-280W-Step-Down-Buck-Converter-7V-40V-To-1-2-35V-Power-Module/192337508944?hash=item2cc8357a50:m:mKFxXwzaQeLUQA8Maz0fJpQ&frcectupt=trueAm I going in the right direction and would something like this work?Do you have any recomendations. What would you change and why?All suggestions are welcome.Thanks,Sven

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 11:26:56 am
content: None of eBay links work for me. You shall note that BMS boards are not chargers, they are *protection* boards. You need current-limited chargeranywayin addition to BMS, better it is voltage-limited as well because most BMS will trip too late - when battery is long overcharged. You don't want to overcharge because it reduces battery lifetime.

author: Pexy13
author_rank: Regular Contributor
timestamp: June 13, 2019, 02:47:15 pm
content: I fixed the ebay links.He will use a bench power supply to charge them anyway but thanks for the info.

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 03:53:34 pm
content: Quote from: Pexy13 on June 13, 2019, 02:47:15 pmWell... I would not do it. You don't want to leave *any* chances for Li-Ion charging to go wrong - because it may end with fire. If current capability of that supply exceeds max charging current of cells - you badly want to introduce switching charge regulator with adjustable both voltage and current. Those 4s "balanced" BMS looks good - in case they work as promised and tresholds are within specs. 5V USB board looks very good, just make sure to use screw terminals. BTW if you are getting used 18650 cells - make sure to measure their capacity using smart charger and balance your battery bank well.

author: Pexy13
author_rank: Regular Contributor
timestamp: June 13, 2019, 04:23:33 pm
content: So you think that I should also add a charging regulator? Im not completely sure what to look for so if you would send me a link to the regulator I would appreciate it.I have a battery charger I used for my RC cars and stuff so i can check the capacity whit it to balance the pack.

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2019, 04:57:19 pm
content: Quote from: Pexy13 on June 13, 2019, 04:23:33 pmI tend to be on safe side and do not leave place for human error, especially if it may damage battery cells or burn my house down.QuoteIMAX B6 clone + appropriate 12VDC (6A) supply. This BTW is balance charger meaning youmaythen use "plain" BMS w/o charge balance function.

author: Pexy13
author_rank: Regular Contributor
timestamp: June 13, 2019, 07:41:03 pm
content: The battery charger I was talking about is a similar product like IMAX B6 and is also a balance charger so he can charge it trough it.Thanks

author: mariush
author_rank: Super Contributor
timestamp: June 13, 2019, 08:04:32 pm
content: How much power he wants on 12v ?If you want to keep it super basic, the easiest approach would be to simply parallel all 8 batteries. It's not "healthy" for the batteries and you can't produce a lot of power on 12v, as you'll be boosting 3.7v..4.2v up to 12v but on the upside you'll have super easy charging from a 5v usb port or using a basic barrel jack and wallwart adapter and producing the two voltages can be done with cheap simple boost regulators.For charging, you could use something as basic as a MCP73812 charger chip :https://www.digikey.com/product-detail/en/microchip-technology/MCP73812T-420I-OT/MCP73812T-420I-OTCT-ND/1979800It takes in up to 6v (from a usb port or barrel jack connector) and charges batteries with up to 500mA ... divided by 8 you get around 40mA per battery, so it's slow enough to not overheat the batteries, to balance themselves out by some degree and so on..You'll find tiny circuit boards with this chip or others in the family, like MCP74832, where you have DC input and battery connection and maybe an option to select maximum current (up to 500mA)If you want slightly faster charging but similarly simple chip Skyworks has one that can charge at up to 1.6A :https://www.digikey.com/product-detail/en/skyworks-solutions-inc/AAT3693IDH-AA-T1/863-1512-1-ND/4246137That's around 200mA per battery, if you have 8 batteries in parallelIt's a bit more difficult but you can solder thin wires to the pads, for example you can get a solid core ethernet cable and take out the 8 wires inside and solder the wires carefully to the padsYou can get step-up dc-dc converters which can convert low voltage to higher voltage with reasonably high efficiency.Here's a couple examples:up to 3$ each, up to 2A of current :https://www.ebay.com/itm/DC-DC-Boost-Step-Up-Voltage-Regulator-3-3V-4-2V-5V-6V-9V-12V-2A-Converter-Module/322590885144(select from drop down list 5v or 12v output, you can manually change voltage by changing resistors on the circuit board)12v only (seems like same chip) :https://www.ebay.com/itm/Mini-Step-up-Converter-DC-DC-3V-3-7V-5V-6V-to-12V-Boost-Voltage-Module-Regulator/112855472220up to around 2.5A of current, select voltage from drop down list :https://www.ebay.com/itm/3-5A-DC-DC-Step-up-Boost-Voltage-Converter-Module-3V-3-3V-3-7V-to-5V-6V-9V-12V/2826306749511.2$ up to 1.2A of current, 12v out version (you can change resistors to get 5v out) :https://www.ebay.com/itm/DC-3-3V-3-7V-5V-6V-to-12V-Boost-Voltage-Regulator-Converter-Step-up-Power-Supply/2718121054432$ : fixed 5v output, maximum 0.48A, up to 85% efficiency :https://www.ebay.com/itm/DC-Boost-Step-Up-Converter-1-5V-3V-3-7V-4-2-to-5V-Voltage-Regulator-Power-supply/172438981311