Just finished building my pack but need help with the design.

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pankajdas

New member
Joined
Sep 24, 2021
Messages
14
Hey guys I am pretty excited to share my first DIY powerwall build (well I was able to find only 83 good cells so not exactly a power wall). All the cells are above 1500mAh and in total I have roughly 540Wh of energy. It is low for many of you but for my small house it is fine as my house doesn't need more than 2kWh per day and the peak load is not more than 500w at once which is for short time also. I need some help with the design because I want to expand my pack in the future as I find more cells without disassembling my current pack. I'm charging the pack with 200watts of solar. It is the starting of my powerwall journey so any help, tips, and guidance are appreciated.

Edit - I am not using a BMS right now because it hasn't arrived yet. I have ordered Daly DL7s 50Amp bms. I am checking the voltages of each pack every 2 hours and the voltage difference after using it for one day is 0.08v. I will be using the pack with me monitoring until the bms arrives.
 

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Redpacket

Member
Joined
Feb 28, 2018
Messages
1,330
Be sure to add a circuit breaker.
Maybe you could make similar 6P modules and add a batch of 7 to your existing 7s system via the screw terminal blocks for now?
Maybe you could use eye terminals on the red and black leads & join with a bolt.
Look at pictures from other users to see ideas they have used.

Be careful with pack balance & do not over-charge!, Max 4.1V/cell, min 3.0V/cell.
Maybe if near full, monitor more often until BMS arrives?
You should have an MPPT charge controller between panels & cells to limit max voltage & get the most power from your panels.
 
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J_Mack58

Member
Joined
Apr 7, 2021
Messages
92
I see a nice 7S12P there Pankajdas. All the safety precautions Redpacket mentioned are valid and you need to do them. But getting back to your question on expansion, first you have to get a layout where everything is solid. I'm drawing your layout now. Then if you can get more terminal blocks and double them your expansion will be easy. See my picture? I'm willing to send you this type of terminal with the jumpers you need to cut. they go in the center. So now when you build 7 more 12 in parallel or what ever all you do in wire them in. Hopefully you will have your BMS by then. It's the double or triple terminal block you need if you going to build your powerwall that way. I'll send you 8 sets of 3. I drew the diagram with only 2 but I know you may expand to 7S1TrillionP I can only get you so far.
 

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J_Mack58

Member
Joined
Apr 7, 2021
Messages
92
Almost forgot you need the DIN Rail the terminal blocks attach to. I'll send that too. 8 of them 100mm long. But if you are careful and had plenty of wire you could put all the terminals on one rail in the vertical direction and wire that way. Let me know if you need a drawing.
 

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Oberfail

Member
Joined
Jun 22, 2021
Messages
103
Neat pack! But ff you're going to expand your pack on the go, i reccomend you to overhaul your current one.

Its not the best decision, to have the + and - wire coming from the same side, as that increases the resistance for the batteries at the end of the pack and puts more stress on the first cells in that pack. Not a major issue with your small pack, but it becomes worse if you're going to daisy chain them.
1635369361169.png
This would be the ideal configuration. ^

You could then build a small shelf with busbars to store them in like another User here did. Neatly organzied and plenty of space to expand ->
The image i mean Source: https://secondlifestorage.com/index.php?threads/new-power-wall-mures.6546/post-79349
 
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