My little ~2 kWh Powerboard

DarkRaven

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Sep 2, 2017
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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 bea wooden board sitting there in the corner of my livingroom for various power-relatedapplications. As of the recent planning stage it will be a bit less than2 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-gridof course.


It is a very small and simplesystem 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 yearI 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 beingrecycled 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 supercheap, 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 priorand 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 thengot a whole bunch of batteries for freewhat turned out to benew old stock from a mate at work. I'm working with server-related stuff, he works at the department reponsible for all our personalcomputers 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 batterieseither 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 cellsstill 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 LEDflashlight 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-friendlyand "free" solar power.
It doesn't end there of course, there arealso my powertool batteries which are a bit chunkier in terms of capacityat 18V with5 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 andwill alsoprobably 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 isthe 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 maybesomething 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 0C for extended periods of time. With the lead acid batteries I have far less concerns and the 18650s Iwill 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 1,5mm solid copper wires for a total of 4,5mm or 6mm. That is plenty for what I have planned. Connections to the cells will be made with 0,2mm 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 surelyit 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 courseis the main reason why I have joined what looks like a very nicecommunity. I'm also completely open for ideas to improve certain things. If you have any, make sure to let me know!
 

Wattsup

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Feb 19, 2017
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Good read and sounds like a good plan :cool:
 

DarkRaven

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Thank you so much! Progress will be limited overthe 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!
 

DarkRaven

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Small update, nothing much happened though. Having like 15 things to work on at the same time, waiting for stuff and so on.

Got some pictures though, I know you like pictures!

They show my testing setup before and after todays modification, I made a unified power supply for the MC3000s and mounted fans on them after cutting holes in their back sides. They are running cooler now while discharging, but the important thing is I now have their stock fans disabled. They weren't that bad but it is much more convenient like this.
On the MC3000 you can have the fan controlled by setting a temperature threshold (like 30, 35, 40, 50C), by setting it to automatic or by having it on or off all the time. The automatic settings have some kind of rpm control, the fan at lower than max rpm can make quite an annoying sound so always on or always off it is. But you have to go into the config and change it there, gnah no, I'm not doing that. If I want to turn them off now I can simply unplug them from the PSU.

Other pictures show my boxes of already tested cells that I will retest on the MC3000s. And the ones on the table are my recent test batches. The cells in the 18650 holders are my seven prepared packs for the powerboard, but I'll retest them as well.

I got also got someone working on copper busbars, not for the packs, but for the board to distribute power there. Will post pictures as soon as I get them.


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Korishan

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Yes, yes, we likey pictures! :p

Well, they shouldn't overheat with those fans installed ;)
 

DarkRaven

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Before that they didn't overheat either obviously, it is just nicer now :)
With the stock fan the system temperature got to about 70-72C when discharging four cells at 1A. Now the temperature is down to 37C. Looks like I can lower the fan voltage a bit :)

I think I'm at 500 cells or something like that and have 45 laptop batteries lying around, waiting to get processed. Capacity of the packs was planned at around 70-75Ah but that might change now as I'm redoing them anyway. Still aiming for around 2kWh of energy though ;) There is not much space to go bigger.
 

DarkRaven

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I got a preview picture of the busbars. They aren't here yet, I got the picture in advance. These will make the parallel connections on the lead acid batteries as well as on the powerboard to do DC distribution.
These are the ones with M6 threaded holes, I'll also get another four with holes without threads just to test to see what method works better or is beneficial in some way or another.
It is solid copper 12x5mm, should be good enough for a couple of hundred amps :)


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wim

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Apr 6, 2017
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Looks good... i have used the same copper bars (15x5mm)in between my packs, also threaded M6, works fine.
I have used brass screws and a copper washer to make a good connection.
For the bigger lugs, just a hole and M8 or M10 nuts and bolts, those copper bars have not enough "body"to thread bigger than M6.


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DarkRaven

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I've retested all cells and rearranged my packs, it is 7S40P now. The lowest capacity cell I used is 1960mAh I think and the average is probably something like 2100mAh. Total energy is now about 2.2kWh. Once assembled I'll test the usable capacity and energy. I didn't use Repackr this time, instead I rely on statistical randomness to even the packs.

Once assembled there will be a theoretical maximum of 577mA of current per cell and that is never going to happen. The usual maximum will probably be more like 100 to 200mA. Most common application is probably charging my phone and that means 23mA per cell :)
 

DarkRaven

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Two months later, a quick update of what happened in the meantime :)

A while back I got some new toys, like a Junsi iCharger 4010 Duo, a DPS5020 and a Meanwell 1kW 48V PSU.
This week I found the time to build my busbars:

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Not the greatest craftsmanship, but oh well. They are three solid 1.5mm wires twisted together, so total area is 4.5mm. Seemed appropriate for a 40p pack with cells tested to 1A, they will handle 40A. I will never use 40A though, so they are more than fine.

Today I've used the first two of them to build the first of seven packs:

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The cells weren't charged, so I'm doing this now. I started at 30A and everything is fine. The pack will handlemore obviously, but the 4mm banana plug connectors, the 12AWG wires and the clamps won't. Maybe I'll use the synchronous mode of the 4010 with double 4mm connections and 10AWG wires to go 2x20A or 2x25A.
I will test the usable capacity of the packs to see whether my random cell distribution worked. Doing that at 20A probably which is a realistic maximum for the packs.

Getting appropriate fuse wire wasa bit difficult, but a friend helped me out with some stranded wire and the single strands are 0.26mm / 0.05mm / 30AWG which will certainly fuse pretty quickly on a 40p pack.

I sill haven't got my battery powered spotwelder which I wanted to show, but it will be on its way very soon (I hope). In the meantime we can say hi to these little badboys:

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My RC days are gone and I've missed a bit of technological progress as it seems. These belong tothe latest generation of RC LiPos, 6Ah capacity and 65C continuous discharge, 130C peak. That's 390A/780A. The iCharger calculates the resistance of the cells including wires and connectors to 0.8mR. Just crazy.You can't really use 390A continuous on these as the internal connections as well as the main cables and the XT90 connections will just give up. I haven't seen any specs from Turnigy, but SLS sells this kind of LiPo as well and they say 65C for 20s maximum.
Good enough for thespotwelder though and I will use two to power it. Tests have shown that one battery is enough because the pulses are very short but I like a slightly bigger margin.

Just thoughtI will probably make a new thread for the spotwelder though.

So, yeah, progress is slow, but there is some :) I will build the other six packs in the following days and then we see what's the worth of statistics when distributing cells :) I think it will be fine though.

And now I will go and fix my fume extractor, something in there went haywire. The second fan suddenly started turning the other way as if polarity was suddenly reversed or something...
 
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