LiPo interface for Arduino Nano BLE - Page 1
Forum section: electronics / beginners

author: jtruc34
author_rank: Regular Contributor
timestamp: July 07, 2022, 08:06:43 pm
content: I have a very simple project involving a bluetooth board (Arduino Nano 33 BLE) that I'd like to supply with a 350mAh LiPo battery (https://www.distrelec.ch/fr/icp-batterie-accumulateurs-rechargeable-li-po-7v-350mah-renata-icp602823pa-01/p/30158722?track=true&no-cache=true&marketingPopup=false). I'd like to get a prebuilt solution to charge the battery, to step-down the voltage to 3.3V and to cut off power when the battery is discharged. The only interface should be a USB-C connector to charge the battery, an LED to show the charge status and a switch to turn everything on and off.At first I would prefer it to be available on a Swiss website, but the only solution I found on Distrelec washttps://www.distrelec.ch/fr/mcp73831-lipo-battery-charger-and-pam2305-dc-dc-converter-module-xinabox-pl01/p/30180705?trackQuery=lipo+charger&pos=1&origPos=1&origPageSize=50&track=true, and it's rather expensive, and isn't even suited for the battery I use which have a recommended charging current of 175mA.I have several questions:- Should I specifically look at something that cut power off when the battery is discharged, or does the battery I mentionned have an internal protection circuit that cut power off at the right moment?- Should I look at a buck-converter, or should I expect to realistically use the battery to go under 3.3V and thus use a buck-boost converter?- As I couldn't find any monolithic solution, what solution should I choose?- Is 50mA a realistic average current draw for the Nano 33 BLE? Otherwise I should pick a bigger battery.Thank you for your help.

author: jtruc34
author_rank: Regular Contributor
timestamp: July 07, 2022, 09:31:02 pm
content: I can answer the first question, which is that LiPo batteries usually come integrated with a protection circuit that cut them off under a certain voltage limit.

author: jtruc34
author_rank: Regular Contributor
timestamp: July 07, 2022, 11:37:33 pm
content: I think I solve my issue, but please comment my solution, as I'm not entirely sure. I think I'll use another board instead:https://www.distrelec.ch/fr/carte-de-developpement-bluetooth-wio-lite-mg126-atsamd21-cortex-m0-seeed-studio-102991186/p/30159343?trackQuery=bluetooth&pos=16&origPos=11&origPageSize=50&track=trueIt has an integrated charger circuit (CN3065) and is much cheaper. As all I want to do is pull a binary signal at very low frequency and send the result on bluetooth, I don't need anything more. I can show the battery status by measuring the voltage through one of the ADC of the microcontroller.I have one remaining question. I read that the ATSAMD21G inside the Seeed board has a consumption of around 5mA during while loop, about 2mA at idle and sub 50uA in standbye modes. The MG126 draws 20mA while transmitting and 50uA otherwise. Is 25mA a good higher bound on the average consumption (knowing that my system will have an update period of about 200ms), or does the whole power supply thing on the board make the power consumption much higher? The other peripheral I'll hook onto the GPIO should have minimal power consumption (mostly switches).Thank you for your help

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 08, 2022, 07:27:59 am
content: tl;drWhy not thinking about using the PCB from a powerbank? Comes with all you need: USB charging input, battery over-undervoltage protection. The only to do, is modifying the output boost-converter to 3V3 - if possible.Capacitance of battery seems less important, so you can mount an much smaller one. I don't think, they are counting Coulombs durig charge, but using only an voltage controlled charging algorithm.In that example fom TI, Vout (Min) is 2.9 V (TPS61236P)https://e2e.ti.com/blogs_/archives/b/fullycharged/posts/your-complete-power_2d00_bank-solution

author: jtruc34
author_rank: Regular Contributor
timestamp: July 08, 2022, 02:25:30 pm
content: I thought about this, but I think the solution I came up with is cheaper, if it works. If it doesn't, I'll just integrate a powerbank which come with a 5V output which I can feed in almost any uC board.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 08, 2022, 02:52:43 pm
content: complete Powerbank 10.000mAh (Logilink), USB-C Input, fast charge was at 9,99€ (Aldi-Süd)

author: Peabody
author_rank: Super Contributor
timestamp: July 08, 2022, 09:19:37 pm
content: Power banks are designed to charge batteries, not to power projects. They have bad habits, like turning off if load current gets too low, as when the processor goes to sleep. And it may not be possible to use them in UPS mode - some power banks shut down for a second when mains power is connected or disconnected. And many won't let you power the load and charge the battery at the same time.

author: jtruc34
author_rank: Regular Contributor
timestamp: July 08, 2022, 10:42:06 pm
content: But does the solution I suggested seem ok to you? It's around the same price, for about 175mAh (Ok, it's around sixty times less, but it shouldn't be sufficient for my application, shouldn't it?), and the board I mentionned come with a charger module integrated. Does it offer enough protection?Quote from: Peabody on July 08, 2022, 09:19:37 pmI hadn't thought about that.

author: Peabody
author_rank: Super Contributor
timestamp: July 09, 2022, 04:15:47 am
content: I have no experience with SAMD processors, but it looks ok to me. You would need to power it from a 5V mains USB power supply, or possibly from a power bank, but either way you would need a separate battery for the module. However, you should study the schematic and manual PDFs from that link you posted.

author: Kasper
author_rank: Frequent Contributor
timestamp: July 09, 2022, 10:06:13 pm
content: Quote from: jtruc34 on July 07, 2022, 09:31:02 pmMany do come with that but once it trips, most chargers will see Vbat = 0V and they won't charge it.LiPo chargers usually won't charge when Vbat is too low.It's better to monitor battery voltage and shut down well before it gets too low. Particulary if you expect users to use it until it shuts down and then leave it for a year before charging it. Keep in mind even after you shut it down, there is still leakage current.LiPos are usually more complicated and dangerous than good old rechargeable NiMH batteries. Have you considered AAA battery(s) instead of LiPo?