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First DIY powerwall (14s40p)
#1
Hello,

(Sorry for bad english)

As i took a lot of advice from this forum to build my first powerwall (14s40p 4.7kw max) from refurbished cells(from computer batteries), i share here my build and the errors i've done :

- the project is long time consuming : to have all the batteries (tested and regrouped), to make the buses, to solder them (glass fuse on each cell positive), to assemble, to test,etc.







Errors and return of experience :

- When i charge all batteries before assembling a cell of 40p, i forgot to charge some and i have to dissasemble cells that where very hot after soldering (normal: others charging hard the not charged cells) : advice check, double check, triple check and be organized (not as me Sad )



- When i created the buses (technique: 3 wire torsaded with driller), i didn't make them at exact size so when i assembled the 14S some holes where not in front of each other).Not an error:I made also the busbar of each side (+ and -) of 40p so the current can well circulate (saw this on youtube video)



- Difficulties to solder on busbar: i have a good soldering iron (80w) but i made bad soldering from the cells to the busbar : one of my cell was unbalanced, it was flagrant when i charged the entire battery with 14*4=56v so each element would be next to 4v and i have one that was at 4.21 and the others at 3.95 ... after inspecting the 40p cell, test continuity, i saw bad soldering (8 cells where "disconnected").

- For the discharging testing, i've made a approximatively 170w/3A of 2 series of 5*12v halogen bulbs (it is slow but nothing else as simple i've found: i will put car bulbs to drive more watts perhaps)

- For the charging, i have some rc chargers (max 10s) but for the 14s i've build a 24v power supply made from 2 server power supply (one with isolated dc ground) that can do 69A : But i'm only using 23a output from this power supply to a converter (advertised 1500w, cc,cv) booster for a 8/9a charging at 56v: it works great but you have to put a fan on the converter.

- I've tested a 14s 1.2a balancer, it works well the first time (it was balancing my cell thas was bad soldered taking juice from the adjacent ones) but second time i use it, it blows with smoke (and a beginning of fire) ... trashed. 



I'm looking for a bms (100A approx) and will use this powerwall hooked to a solar hybrid inverter (replacing 4 flooded batteries in series).As i'm looking  for the bms (perhaps chargery), i'm thinking of buying a small bluetooth bms just for looking at cells balanced voltage so wiring only the balancer part but not sure it will work instead of hooking a 2*powercell meter (8s): i don't have good (cheap) solution to visualize the cells voltage (and i don't want to put 14 litlle voltage meters..).



Regards.
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#2
Welcome, nice pic, and congratulations on creating your 14s battery!  

> have a good soldering iron (80w) but i made bad soldering from the cells to the busbar
I use 6AWG twisted copper (for buss) and 100w soldering iron.   80w might just be a bit cool if your bus is 6AWG or larger. 


>I'm looking for a bms (100A approx) and will use this powerwall hooked to a solar hybrid inverter (replacing 4 flooded batteries in series).As i'm looking  for the bms (perhaps chargery), ....
Strongly suggest a 14s BMS.   Dual 7s won't keep the 2 halves in check properly.   I've had mixed success with Charger - 1 worked and 1 burned up internally for no reason, but it is on the cheaper side.  

>the project is long time consuming : 
Yep...  Over 3 years, 10,000 cells (and counting) it has become addictive - but fortunately is A LOT OF FUN as well Smile
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