Begginers Guide to Processing 18650 Cells | Cell Database


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My little ~2 kWh Powerboard
#1
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Intro / tl;dr

Powerboard is the name I just came up with, basically a second ago for the sake of being able to name it something other than mini powerwall (what it will be really). It will literally be a wooden board sitting there in the corner of my livingroom for various power-related applications. As of the recent planning stage it will be a bit less than 2 kWh and not directly connected to my solar. So there is some lead acid involved as well and the 18650s on the Powerboard are some sort of 2nd stage behind the solar and lead acid. This is 100% off-grid of course.


It is a very small and simple system in comparison to what some of you are building here but I thought I'll post this nevertheless. Maybe it will serve as some kind of inspiration for others or someone just finds it interesting for some reason or another.

So, if that sounds interesting to you and with the tl;dr out of the way, let's get started! Be warned that, as of now, there is just text involved about what I've done so far and what the idea is, there isn't much to show you yet!
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The Story:

Earlier this year I wanted to harvest some old notebook batteries to build a stock of used but still usable 18650s for various little projects that would require some sort of power source. And I wanted to prevent some still good cells from being recycled for no reason when they were still usable. I aimed for about 50 cells or so which would have been plenty. But as it happens so often, it all escalated a bit quite quickly after I disassembled the first few notebook batteries. I was able to buy about a hundred batteries for about 1,50 EUR per piece. This wasn't exactly super cheap, but I considered a decent price given the prices asked for at most places around here. The result was my first 200 or so cells I deemed worthy of keeping. They have between 1500 and 2100 mAh.

This was a couple months ago and at that time I decided to do something in terms of solar storage with these. I moved to a different place about half a year prior and have a nice, south-facing balcony now that is in full sunlight for almost the entire day. No trees or other buildings in the way. I don't own a house, I'm single and living in the city, so this is probably the best I could have got to be able to do something with solar power.

I then got a whole bunch of batteries for free what turned out to be new old stock from a mate at work. I'm working with server-related stuff, he works at the department reponsible for all our personal computers and he gave me a lot of batteries that were to be disposed of because of their age. They were for models of Lenovo ThinkPads no longer in use, like the T400 if that means something to you, so we had no more use for these batteries either since the T400s didn't exist anymore. I originally asked for any kind of notebook batteries and mostly thought of dead ones they were going to throw away. However, it turned out that these batteries were old calender-wise, but hardly used cycle-wise. Most of the cells still had their original capacity of about 2600 mAh.

The Idea:

I have a corner in the livingroom that I can't really use for anything but it seems a really good place to fit some kind of board where I can attach several power-related components to charge all my battery powered devices from solar power.

This includes all the obvious stuff like mobile devices, smartphones, notebook, tablet and the likes, the 18650s for my LED flashlight and a wireless headset. This is strictly low capacity stuff, but something I have to charge on, up to, a daily basis, so why not change this to juicy, eco-friendly and "free" solar power.
It doesn't end there of course, there are also my powertool batteries which are a bit chunkier in terms of capacity at 18V with 5 and 6 Ah. The vacuum cleaner runs off a lithium battery as well.
And so on and so forth, the list probably isn't complete and will also probably grow in the future as well.

Also I wanted to be able to power 230Vac devices from the solar power.
But first, many of these devices come with their own AC/DC powersupply and getting rid of them is part of the plan. There is no need to do the AC/DC conversion all the time, I'll aim for a more efficient DC/DC conversion for these devices.

And then there will be a 12V 500W inverter to provide some 230Vac if needed. That is the case for the smartphone charger for example. Only with that thing I'm able to use the "proprietary fast charging via USB technology", in my case the Dash Charging from OnePlus.

The Setup:

The solar power comes from a single 150W panel connected to a EPEVER Tracer A3210 and is stored in a 12V 120Ah AGM Deep Cycle lead acid battery. That works surprisingly well. I have set my aims pretty low but even with a suboptimal angle of the panel I saw almost 10A going into the battery continuosly as long as there is some decent sunlight. That is more than I expected. 10A was the peak as far as I have witnessed.

I will not have the lithium cells connected to this system directly for various reasons I will cover in a moment. I will just charge them from this system.
First reason for not doing this in my case is the complexity of a lithium based battery on a system designed for lead acid batteries. It is not impossible and there is also the first MPPT controller for lithium batteries now but that is maybe something for the future.
Second reason is the upcoming winter. Here in Germany the situation outside might not always be viable for storing lithium batteries outside. At least in my book. I'm not comfortable with leaving them outside with temperatures well below 0°C for extended periods of time. With the lead acid batteries I have far less concerns and the 18650s I will keep inside where they stay warm. There will be no load on them when I'm not home so I consider this reasonably secure.

And with that we finally come to the 18650s themselves. I will use a 7S setup, so basically a 24V system. As of now I have arranged the cells in 30P blocks with about 74Ah each. With a nomimal voltage of 25.9V and 74Ah that will be a bit more than 1.9 kWh.
I went for a higher voltage here, 24V instead of 12V on the solar, for future developments and ease of use since 12V 3S or 4S isn't really suitable for me, more an that in a moment. Solar can be upgraded to 24V easily if that might become a thing. The final Powerboard will have a 24V to 12V DC/DC converter as well to power the 12V inverter and the SkyRC D400 which runs on 11-18Vdc so it can't be powered directly from a 24V system. This charger will be used to charge other batteries when powered from the lithium cells and to charge the lithium cells from the solar / lead acid battery. For example I charge a 4S3P LiFePo4 battery with it, this is a 12V 36Ah battery I use for several generic things and extended solar power storage as well. Will be able to power the Powerboard as well in case I don't have the 18650s charged.

12V on the lithium batteries on the Powerboard wasn't an option for me, the voltage range for a 3S or 4S setup is just very disadvantageous. That's another reason why I went straight for 7S and a DC/DC converter for 12V.

I tried the ***** kit first to assemble the cells, but I wasn't completely convinced. I thought about spotwelding for a moment but that will probably be something for the future once the kWeld ist available again. Google it if you are interested, it is a battery powered spotwelder which is working very well as it seems. For me this is a much more convincing method than reused microwave transformers and the likes.

So for now I used the classic approach with 18650 holders and soldered the connections on the cells. At the moment I have all seven 30P blocks prepared in their holders and tinned their terminals. A 300W soldering iron with a 350g copper tip did the job very well.

To Do:

Next thing will be the busbars for the cells. I will use three or four 1,5mm² solid copper wires for a total of 4,5mm² or 6mm². That is plenty for what I have planned. Connections to the cells will be made with 0,2mm² solid copper wire which should be good for about 5A max so it will provide a fusing function if something goes wrong. I haven't tested it yet but as I see it surely it will never be able to withstand 15, 20 or even more amps for prolonged periods of time.

So, yeah, from here on I will keep you updated on what happens and will also provide pictures. I wanted to keep it brief, turned out to be a wall of text once again. Happens to me quite often, oh well, what can you do! I just wrote this down from the top of my head, I hope it isn't too chaotic and unorganized for an external reader. It all makes sense in my head, I promise!

Please feel free to comment or ask questions if you have any, this of course is the main reason why I have joined what looks like a very nice community. I'm also completely open for ideas to improve certain things. If you have any, make sure to let me know!
BlueSwordM and Korishan like this post
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#2
Good read and sounds like a good plan  Cool
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#3
Great plan! Pics are welcome here as well!
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#4
Thank you so much! Progress will be limited over the next weeks or so, but sure, I will post pictures as soon as I have something to show. I'm kind of working on several things at the same time at the moment!
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