CMG's PowerWall

cmg_george

cmg_george

Member
Joined
Oct 24, 2017
Messages
84
Hi all!
I'm George from Romania, it is nice to e-meet you all. Thanks a lot for the information shared on this forum!
I was thinking since long time about a DIY solar system to reduce my electricity bill and to get as much independent from grid as possible. My plan is to have a 10kw battery pack in the future... but i will do it baby steps. I plan to start with a 100P3S and use that for lighting. Power will come from 10 solar panels. I hope to install 3-4 of them this year if the weather will allow me (i hope will not snow in November).

Currently it start harvesting 18650 from laptop batteries, change and test them. For charging i'm using tp4056 (8 at the moment)(+ one cheap china charger which i got with a flash light) and for capacity test i built 2 arduino based tester. I can check 7 battery at a time (actually 6 until i will receive more 18650 holders). My budget is very limited so i can not invest in commercial capacity testers.

I have a hard time finding cheap laptop batteries... any suggestions/help is very appreciated!
From the one tested until now i also have a very low rate of good cell. I decide to use everything above 1700mAh.
I also have a lot of questions and i think is best to put those questions correct threads.

PS: Anybody from Romania here?


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Well it looks like your off to a good start. I'm new to the forum but have already realized I tend to enjoy reading about the smaller scale builds then the larger ones. More home grown electronics and such.To me its a big advantage that you can put together your own electronics to build some of the equipment you need for testing etc. Looks like some very neat work also.

Will be interesting to see how your project progresses. Good luck with your build CMG.
 
Nice little setup you have there. Just to clarify, are you building your packs with 100p and then putting them in 3 series, or, are you taking 3 cells, connecting them in series, then connecting those in parallel to make a 100p? Based on your first post, you are doing the 3 cells, 100p connection. If the pack is 100p, then it would be 3s100p ;)
 
kennl said:
Well it looks like your off to a good start. I'm new to the forum but have already realized I tend to enjoy reading about the smaller scale builds then the larger ones. More home grown electronics and such.To me its a big advantage that you can put together your own electronics to build some of the equipment you need for testing etc. Looks like some very neat work also.

Will be interesting to see how your project progresses. Good luck with your build CMG.
Click to expand...

Hi Kennl, to be honest is not that hard to have the electronics for testing the cells. Most of the credit goes to Adam Welch , i just changed the code a little to have the option to check multiple cells at once and a nice interface to view the discharge progress.

Korishan said:
Nice little setup you have there. Just to clarify, are you building your packs with 100p and then putting them in 3 series, or, are you taking 3 cells, connecting them in series, then connecting those in parallel to make a 100p? Based on your first post, you are doing the 3 cells, 100p connection. If the pack is 100p, then it would be 3s100p ;)
Click to expand...

Korishan, you are right. I will have 100p and 3 (13 at some point) in serie. So 3s100, Thanks!

I would like to keep the cells between 3-3.1 and no more than 4.1V any recommended change controller and balancing BMS?
 
For 3s the Batrium seem like overkill but if you plan to expand beyound 14s (Or 13 if thats your goal?) then it is costworthy to what you get if you ask me.

if not you got RecBms, TinyBms as 2 choices and there is more out there. I whish someone could send me a sample of each so I could test them :D
 
I read about Batrium... is way out of my price range (for the moment). I target 13s... never know after that but first i want to setup first 3s like a prof of concept and to see how is working. If i manage this i will continue with the build. Never know were i will say stop... dismounting laptop batteries seems addicting :D
If i made my lessons right i hope i plan this correct: solar panel will provide current, inverter (with charger) will put current in batteries and convert to 230AC (from panels or from batteries or from grid in some cases). BMS will take care of batteries health (protection and balance the packs). Not sure about inverter also i just start reading about those but for sure i will not go with a grid tie one since i'm not allow to put power on grid and i want my system to work when grid is down.
I know that using this approach i will use in the beginning some cheap/low performance components (inverter, charger, bms) and i will throw them away if everything will work but is important for me to see that the system works and i can handle it.
 
Ok, i don't know why i was thinking that for a 48v system it will be 13S, i was wrong, so i think the correct is what i will target 14S actually.
I found @owitte powerwall build: http://secondlifestorage.com/t-There-s-a-new-wall-in-Germany and i think is brilliant because it is very easy to upgrade and maintain. Any disadvantages on this build? Looks like this will allow me to start directly with a 48V... i must measure the available space to see if i can fit 14S with this build type.
 
Its a cool setup if you can afford the wall-space. i personally think a cabinet or such is better storage wise since my wall space is limited :)
 
I redesign one of my capacity tester, is now more compact.


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Also the "trash bin" with the things i blow up is bigger now :(


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I also order some cells from @Kaspars Krumins waiting for delivery.
The space where to put de power wall was set, i will follow @owitte approach. How ever i need to delay the inverter and solar panel purchase so probably the system will go online in spring.
 
No, it does not have. I don't have any analog pin available on the Arduino ( for a thermistor).
However, during discharge I didn't found (until now) any cell to get hot.
 
I start building first packs. Each has ~37500mAh.
The red one (solder one) is for tests only. I will use it to figure out the exact space needed (total height and distance between pipes).
I need to wait for some more holders... china delivery is slow (or maybe because of local post).




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Mean while i found the mother of laptop batteries (don't know if this deserve a separate threat):
12cells in one pack


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That's a big pack. the biggest I have pulled apart is a 9 cell.
 
Following @owitte design this is how my wall will look like.
Any idea on a flexible connection between the pack busbar and main (copper pipe) busbar (see the picture)?
Any recomandation on the pack busbar dimension?


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why not secure an anderson plug to the pack and bus bar and simply plug it in. loose cabling or loose batteries hmmmmm
make the pack slide into a plug like a socket.
 
The problem with Anderson it that looks expensive and i need also some mechanical support for each pack and i don't think anderson is good enough. I think i will add something like a slot to give some support, make the busbar from this cable:


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instead of the solid one.
 
That wire is fine. Just remember that you'll need to solder all the threads together for each fuse/connection to a cell to give it proper balance.
The Anderson connectors are quite robust. You could probably hang a 4kg weight from it and it'd not separate. You need a lot of force to get them things open sometimes. It all depends on the angle of the lug. But, there are many different type of Anderson connector of different sizes.
A blade/slot connection would be fine (kinda like how automotive fuses are done) for a pack that slides into slot and connects everything up on the same end on the shelf/rack.
 
I would use ring-terminal. And on the wall side of the bus bar have bolts that are stuck to the bus bar. Its just a matter of hanging the battery on that bolt sticking out and tightening it. Easy, simple and no problem with contacts need to take the weight.
 
Yes, the bolts are my fist option also. I was thinking on soldering them on the main busbars. I will give it a try in the next days.
 
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