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rapidly serviceable battery settup
#1
Hi guys,

looong time no post. I have been lurking and designing the chassis for my build and it has taken a long time to land for me as I want to be able to quickly service my modules (P120) and not have to solder or cut anything to do so. props to another forum member AJW22 here for their STL files that i have taken and modified to suit my purposes. Thanks mate!



I have enclosed one side of my battery chassis (Negative will be in black, in the future the positive side will be red) to create a top and bottom opening that will act as a duct for the heat that rises through it. the long mons can sit in the narrowed top opening to measure any difference in temperature as the air flows over them. 


The plan is to have connections via simple sprung battery terminals that are spot welded to 8mm nickel strips running the length of the chassis and with criss cross connections. The nickel and sprung terminals will be attached via a compression plate on each side to match the profile of the chassis and seal off the ends of the batteries. one side will have glass fuses between sprung connection and nickel strip. 


The whole idea is rapid deconstruction when cells need testing/replacing. as I am hoping for 6 banks of 14 modules serviceability becomes the priority. 



8mm nickel strip is cheap. 
the sprung battery terminals are cheap. 
the glass fuses are cheap. 

I am still in the prototype stages but can anyone bring some helpful critique to this design to improve it from here? open to experienced voices.
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#2
hm... the design looks oddly familiar ;-)

Looking forward to seeing how you plan to cram the nickel strip, sprung terminal, and fuse into/onto that.
Remember that nickel strips are very thin with limited current carrying capacity. So you may have to add a thick copper bus, or at least several attachment points between each pack.
Scottietheyoung likes this post
Modular PowerShelf using 3D printed packs.  40kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#3
(10-02-2019, 12:18 PM)ajw22 Wrote: hm... the design looks oddly familiar ;-)

Looking forward to seeing how you plan to cram the nickel strip, sprung terminal, and fuse into/onto that.
Remember that nickel strips are very thin with limited current carrying capacity. So you may have to add a thick copper bus, or at least several attachment points between each pack.

Hey mate,

Thanks again for the design share. I added the stop bars in each cell pocket to give me a consistent distance for spring connection.

Re the packaging the fuses are the real design challenge but will be incorporated into one side of the compression plate that sandwiches the whole thing together.

Re current yes. I will need to calculate my material thickness.
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#4
The 3D printed design looks nice .... but
I don't understand why so many powerwalls are designed with the cells so close together so that ventilation isn't good.

Can someone explain this?
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#5
(10-02-2019, 10:19 PM)Bubba Wrote: The 3D printed design looks nice .... but
I don't understand why so many powerwalls are designed with the cells so close together so that ventilation isn't good.

Can someone explain this?

Because heat is a non issue with these units as current draw is so low.
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#6
(10-02-2019, 10:19 PM)Bubba Wrote: The 3D printed design looks nice .... but
I don't understand why so many powerwalls are designed with the cells so close together so that ventilation isn't good.

Can someone explain this?


As Scottietheyoung says, cooling is not really required for a well dimensioned powerwall.  My typical max charge/discharge rate is just about 0.2A per cell, the average being much lower.  It's too low to create any noticeable heat.

Nonetheless, I've given cooling a lot of thought when designing my packs.  The main motivation being to keep any defective cell from overheating and causing more problems.
Firstly, there is plenty of space under the pack to draw in fresh cool air - very very important.
With the ubiquitous square cells layouts, the airflow would cool just the sides of the cells.  The cell surfaces facing up/down receive hardly any airflow.
With the honeycomb layout, the air has to navigate over all the cell surfaces.  Moreover, the air gap between the cells is actually a bit wider than the typical square designs, which I suppose may just offset the longer path the air has to take.
Bubba likes this post
Modular PowerShelf using 3D printed packs.  40kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#7
(10-03-2019, 12:49 AM)ajw22 Wrote: [quote='Bubba' pid='55335' dateline='1570054783']
The 3D printed design looks nice .... but
I don't understand why so many powerwalls are designed with the cells so close together so that ventilation isn't good.

Can someone explain this?

Also why I like this pack layout thanks AJW. Airflow is enough to provide better than passive cooling if in the unlikely scenario it’s needed...
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#8
Imagine the space extra needed for My powerwall that have 29000 cells. I wouldnt add something not needed during normal load Smile
WuggyBuggy likes this post
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#9
(10-03-2019, 05:51 AM)daromer Wrote: Imagine the space extra needed for My powerwall that have 29000 cells. I wouldnt add something not needed during normal load Smile

you have a 29000 cell powerwall????????  not sure what you are saying above sorry?

Printing off the first of many of the positive side of the chassis. I ordered rolls and rolls of "watermelon red" PLA for the positive side of the chassis... turns out its pink  Big Grin Exclamation Huh Big Grin



looks like I am stuck with Black for negative and PINK for positive lol.

anyway here is the basic concept of the sprung connectors with mechanical attachment to nickel strip. 



from here a sandwich pressure plate on each side screws on to give consistent tension across the surface.



In this configuration my idea was there would be 9 nickel strips terminating (spot welded) onto a wide nickel plate for connection between 120P modules. I was thinking about using magnets to connect between packs (either that or wooden pegs lol)

My question for those experienced in current and draw is what thickness nickel strip would be needed to carry the expected load? lines of 12-13 cells (will connect them across also)
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#10
Im saying that compacting the packs together is key for us doing larger installs Smile
Scottietheyoung likes this post
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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