Begginers Guide to Processing 18650 Cells | Cell Database


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FCDS - FERCSA's charger/discharger station.
#1
Hi!

In the last few months I built my own laptop(yes and it's working great!) and I thought it's gonna be fun if I made a arduino based battery pack for it. Until then I'm using a smbus based panel from a salvaged x60 battery. I know it has a lot of feature I'm mean a lot.. but heey where is the challenge?
So in the mean time I got a lot of old laptop batteries for research and everything, so I got an another idea.. I should build an automatic charger/discharger station for my 18650 cells too.
This two things are very related, because I can use the discharger mosfet circuit for balance my batteries in my laptop, right?

So I started to brainstorming and I came up with a really good solution for my station: stackable charger/discharger modules!
There'll be the master module with arduino and a multiplexer then a lot of slave modules. Each module will accept 8 18650 cells. If you want more just thrown in one more slave module and you already can charge or discharge 16/24/32.. cells in the same time. Of course arduino will control and logging everything! Voltage, current, temperature etc. I'm planning to add wifi support too!

This log from my very early prototype in my laptop. In the current state it's just a battery monitor system:
docs.google.com/spreadsheets/d/15-TjWL1w3QZ-HRGr0dIwD0O4YzJwbcgDjGcCb15BkmM/edit?usp=sharing
Diagrams on the 2nd and 3rd sheet.

3 cells under charging, nothing fancy here right now it's just a simple battery monitor with voltages. Arduino logs everything in a csv file. But first I need to finish the charger station then I'll upgrade it with a balancer and any safety feature, right now there is a blinking led for low voltage..

Anyway if anybody interested in my project(s) I can (b)log my progress here. I'm not a youtuber.. so I'm not gonna make any videos sry, maybe one when I'm finished.

I open for any suggestions, comments etc..




ps.: FCDS = FERCSA's charger/discharger station.
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#2
Hey,
I'm definitely interested. I'm going to be starting work on cell recovery soon. I have some stuff coming in and I will be getting batteries soon. Anything that'd make the recovery and getting status of each cell faster and more efficient, then I'm all for it Smile

Kori
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#3
Cool.
So about the system. There'll be a Master module(stm32, sdcard reader, esp8266), a Slave module(multiplexer, stackable connectors), Battery holders with tp4056s and a Discharger module for each tp4056. The last one is a tiny pcb with mosfet, resistors, connectors etc, it'll sit on top of the tp4056. I prototyped it yesterday with a salvaged mosfet from one of my dead motherboard and it's working great. You can see the result on thingspeak, I just uploaded manually a sample csv, check it out: https://thingspeak.com/channels/220137 In the future it'll be automatic of course. The cell is not in the best shape but for testing purposes it's fine.
Right now I'm waiting for my orders.. multiplexer, esp8266, temp sensors and other stuffs, until then there is not too much to do.

For next step. Maybe I should do a diagram or sort of to how I imaged the whole system.
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#4
Looks good. I see what ya mean that that cell isn't that great for testing. Rapid drop in voltage right off the line :p

What I would recommend for the charts, is instead of having it show "Date", change it to "Time" and show the time in minutes.seconds. It would show a better progression of time instead of 13:10, 13:12, etc. But I know you're in your early phase of it and may of just thrown data in a spreadsheet real quick Smile

You have some pics of what your current setup looks like? even if in alpha stage.

Kori
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#5
In my random video watching on Youtube, I came across the one below. It features pretty much what you had in mind   :p

https://www.youtube.com/embed/lv7xHmc2KW4


*tried to get the embed to work, but the actual posting is broken, even tho it shows the preview in preview mode, odd*
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#6
I think I've a picture somewhere. Let me find it.

Ohh yes the batlab. I saw on kickstarter a few month ago.
I think it's a little bit overpriced, but I've no doubt it's a professional product.

All of them is used parts so don't judge.
[Image: IMG_4013.JPG]
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#7
Hahah, love the "use what you have available" approach Smile
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#8
Just a little update. I'm still waiting for some parts but until then I made some progress on the software side. Right now I've one 16ch multiplexer which allow me to monitor and control 4 cells. It's less than what I excepted but far enough. Anyway my board has 10 analog pins so it means 10 multiplexer aka maximum 40 cells. That's pretty good, I think.



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#9
i am confused why a 16 channel multiplexer only allows for 4 cells to be measured, I would imagine at most, 1 voltage, 1 current, 1 temperature, so 16 / 3 = 5 + ambient temp / voltage reference? or is it just convenience with 4 bay holders

equally, most micros can sample there ADC's at Khz, so long as there input is buffered by say an op amp, or has an impedance of less than 10K, meaning by rights, you should be able to stack these even furthur if you wished, though in its current format it might end up saturating the serial link...

equally is your current load oscillating, i am curious why it would not be more stable, i agree 40mA isnt much, but the batteries should be a very predictable source? (if your using a mosfet, i would have to ask have you fitted a gate resistor)

Now i sound a little harsh, but i just want to help with the small issues if I can.
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#10
Ah IEC 61960 includes a standard way to test for internal resistance.
Wonder how many battery chargers follow that, not many would be my guess.
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