13S8P 21700 honeycomb battery design/diagram

DefconExile

10 mW
Joined
Jun 27, 2022
Messages
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Hi guys , so little rundown I’m wanting to create a 48v 40ah+ battery for my e bike , I’ve mocked up a design on some paper creating 13 groups of 8 cells and was wondering if anybody on here could clarify weather this is a possible design. And also if someone could add if it’s ok the connect these cells in this fashion up in parallel first then series. Another thing I’ll mention is the design may be hard to understand but Surrounded each group of cells with a highlighter so people can determine which cells is part of which group , any input is greatly appreciated this is my first endeavour creating something like this and the design was taken from a larger 13S10P pack however this won’t fit in my bike if I use 21700s
as opposed to 18650 (the cells I’ll be using are 4800mah 21700s)
 

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Give this thread a read to help you understand ideal current sharing:
"Common pack design mistakes, how to avoid?"
https://endless-sphere.com/forums/viewtopic.php?t=84412

Some of your groups only have a few cells that can connect to the next series connection, more is better for better balanced current.
 
pwd said:
Give this thread a read to help you understand ideal current sharing:
"Common pack design mistakes, how to avoid?"
https://endless-sphere.com/forums/viewtopic.php?t=84412

Some of your groups only have a few cells that can connect to the next series connection, more is better for better balanced current.

Thankyou for taking a look , I’ll check that thread and make any changes necessary, better safe than sorry!
 
Ok so I’ve had a peak at the mentioned thread about common design mistakes and I understand the logic being this is an 8p pack , 15A per cell x 8p = 120A. The below chart I have found states that 0.2mm x 0.7mm is optimal for 13A current , I would be planning on using 0.2 x 0.8mm strip so roughly 14A per strip? Also I’m never planning on running this pack anywhere near 100A , the controller a 45A max current so would I be right in thinking that 0.2 x 8mm is adequate , then switch up the design and make sure that there’s 7-8 connections between the series and parallel groups. (Copper plate sandwich method could be used but I’m not sure weather it would be needed and seems a bit more intricate
 

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So I remade the design, and moved some cells around after reading the information provided on the thread above and believe I have rectified the issue being the old design would have only allowed 4 connections in the middle for the series e.g too much juice so I’ve made sure there’s a minimum of 8 connections per series pack , assuming these are 0.3mm x 0.10mm strips of nickel this would allow 9.6A safely through each strip , 8 x 11 = 88A safely through this pack? Could someone with a little more knowledge than me correct me if I’m wrong here would greatly appreciate it. (using 15A 4800mah 21700 cells would be 120A in parralel however I don’t plan to draw high amps through this battery realistically no more than 60A but I’m wondering if I should make sure there’s 11 connections per series pack instead of 8 - 11 x 11 = 121A - )
 

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That was hard on the neck (try and rotate your images before uploading). Your new design looks better. Less resistance between "series packs" is better. You might be able to still improve the layout. In my builds, I've gone with Nickle sheet or using copper sheet + Nickle plated steel strips for the "copper sandwich" method which seems to be working very well. There is a thread on that if you search for it.
 
The two black negative at the very top end need to be relocated. Give it some thought and you'll see exactly where they are a better fit. According to your previous layout it's still basically same pack dimensions.

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What's up with shading those two black negative cells.? You need both those shaded cells to complete the 8p group.
 
pwd said:
Your new design looks better. Less resistance between "series packs" is better. You might be able to still improve the layout. In my builds, I've gone with Nickle sheet or using copper sheet + Nickle plated steel strips for the "copper sandwich" method which seems to be working very well.
Best to have as many series connections as parallel connections (when possible). That lends itself to using "Copper/Nickel Sandwich" buses. More for raw performance use (like pulling 60 amps). Here's a good example of a pack build by thundercamel. If its use was more for raw performance than casual cruising ... then consider cu/ni sandwich buses ...

3RHNG-XrkaSJ1WMOOR-ZYAuTtrOudv1FGcIf63cnTFuLi9R1Oj82sAxVTMsInmaPvuoYzhUNWqHTP4LFlQirlm5wfKyYQrh4IANi9HuBGyxcaBzeFr2NUyvRSollg0qgvPIAyYeb_3tETnVY-MgwwfwkduIEZFtJFy676hIkhtpc6_QnVGlJmjWCEwGwRsGm8k-gsZlj5Xpevgr-JDQwDJUzg38H9qJLe4ZtTFI1oqUDeDegh8zOFNYJNVJOZXkkqjSqPMMSrlyLGi1X_YEjkfL2I-wH3ci5PH_gWMkmFeF-Ab3jwzh7ohfrJ5fDTCAsFrVq1xP7yOrOb7v0mBHbwoIPH7BFxIQcANejTITzGNlWFjKTKFl59EHIyh6WcMsmui8T6vXRZs0MPgsQGw3rm-YTBot6dHTK-LwJRVSYl_LY9nY7uJMyRNgviBNmd3OWPsuUaGApeayUelNV2YZTkjfw7pg9Yvp3oCxy-qCl_MNKV3iZPl-Jq5EaTR82YgPJqzpxboLkk5-VutukaQkhi83r5kY-4sgwsyFcuq2fl118J4bT2kDibRfsP7eKbOYVSIn0nV3WnFJ5yDB4vH-5bnt-j5ElbjHn2Z6eAOYD9rW8D647K5h4ZZsq9gRT-iDNyV1i53xA-_eGA5mXNYhsw0Dsyk1wMTQX-IrgeVH27SwaKjxvxlelcR1c8neJj9g2LxPgS1IJx67-H3hOwB3P0_pe0sE1HoDpX5n0h6qPxweYSlHJYuvI7Q=w4160-h2340-no


You can see how it lends itself to Cu/Ni Sandwich buses primarily for more efficient series connections. Like when pulling higher amp rating during raw performance riding experience.
 
I did some calculations on nickel vs battery resistance a while ago, therefore I really doubt that the posted conductor sheet is useful in battery building. See link: https://endless-sphere.com/forums/viewtopic.php?f=14&t=116001#p1713779

Those that advocate copper/nickel sandwich on 18650 or 21700 cells might also do a calculation what improvements you actually get in your pack - it will increase efficiency less than 1%. I don’t think the butt will feel the extra acceleration or that the thumb will feel the slightly higher temperature. If you’re drag racing then yes, an eighth of a second (or whatever improvement you get) is a lot. All others should be able to use nickel strip alone.
 
larsb said:
I did some calculations on nickel vs battery resistance a while ago, therefore I really doubt that the posted conductor sheet is useful in battery building. See link: https://endless-sphere.com/forums/viewtopic.php?f=14&t=116001#p1713779

Those that advocate copper/nickel sandwich might also do a calculation what improvements you actually get in your pack - it will increase efficiency less than 1%.
Correct me if wrong, but i believe you're the first at ES (since Ron's long running ni/cu sandwich series bus thread) to so imply the following: That being the increased efficiency using ni/cu sandwich series bus plates instead of thundercamel's 14S6P build (just nickel plated copper bus strips) might only be 1% more efficient than his use of just the appropriate (dimension) nickel plated copper bus strips.

It does make sense that the series current flow is more efficient with nickel/copper sandwich series bus plates. Thus the belief more usable cycles are possible when the DIY objective is "raw performance". That said, the recent thinking by some now seems to be: If "raw performance" is the #1 objective (e.g. 100 amps) then better to use more powerful lithium pouch cells (e.g. Salvaged VOLT pouch cells) instead of 1865 or 2170 cylindrical cells ... Right or Wrong or Maybe ??
 
Not right or wrong or maybe. Just physics. If the added heat is too much to accept then it’s better to add a parallel battery string than to add copper. If you can’t add more batteries and don’t mind the extra effort then by all means add copper anyway but with the understanding that the relative improvement is small compared to the battery heating by the internal resistance of the batteries.

When compared to pouch cells the situation is different. There are only a few interconnections so each carry all the current and cell resistance can be as low as a few mohms.. An appropriate conductor size is of course needed there too.
 
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