Battery Questions and layout

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foot8sativa

New member
Joined
Aug 12, 2021
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3
Hi all, looking at building a battery for my ebike build, I have a heap of used NCR18650BD cells, I am testing the capacity and internal resistance of each cell atm. The plan is to build it up as a 14s 6p 50amp 18ah pack.
I have a few questions.
What's the best way to layout the cell groups and connections?
Regarding the internal resistance, what an acceptable difference between cells?
Fuse wire or nickel strip?
Where is a reliable place to get nickel strip? 0.2x10mm? Here in Nz there is not many local suppliers
Cheers in advance.
 

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Wolf

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Sep 25, 2018
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Regarding the internal resistance, what an acceptable difference between cells?
3mΩ to 5mΩ tops the lower the better. Spec call for <35mΩ IR for the cell.
Not sure if the NCR18650BD would be the best choice for an ebike esp if used.
Wolf
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foot8sativa

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Aug 12, 2021
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3mΩ to 5mΩ tops the lower the better. Spec call for <35mΩ IR for the cell.
Not sure if the NCR18650BD would be the best choice for an ebike esp if used.
Wolf
View attachment 25830
Thank you for that, Why do you think NCR18650BD would not be the a good choice for an ebike? 14s6p should be good for 60amps max, i will only be drawing 45amps, I have a heap of old lime e scooter batteries which i was planning to used
 

Wolf

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Ah best choice, good choice, I'm just thinking of the recharge rate of .9A, max of 1.5A, and the IR. Also 0.61A standard discharge rate which basically means that the battery was designed for that in mind. At 6p thats 3.66A. Sure max discharge is at 10A but that's pushing the cell to its limits and your longevity will be impacted.
 

italianuser

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Feb 25, 2020
Messages
358
Fuse wire or nickel strip?
What's important is that connection strips/plates/bars are capable of carrying the max amps your load needs. You should calculate that based on the motor you have. A 500W load on a 14s battery makes about 10amps. Better to have an over-dimensioned connection.
 

foot8sativa

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Aug 12, 2021
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Ah best choice, good choice, I'm just thinking of the recharge rate of .9A, max of 1.5A, and the IR. Also 0.61A standard discharge rate which basically means that the battery was designed for that in mind. At 6p thats 3.66A. Sure max discharge is at 10A but that's pushing the cell to its limits and your longevity will be impacted.
Hi Wolf,
The motor will be a 1500w (1800w max) hub motor with a 45amp controller this will mean it will be drawing roughly 29-34.61amps (4.8-6amps per cell) at max power. I will most likely limit the max current draw to 35amps. I will be planning to use a 5amp charger.
My main concern is the internal resistance, because these cells are used the IR varies alot. Will having a difference of 8-12mohm per cell, will the battery voltage drop too much under load?
 

cak

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Mar 14, 2021
Messages
64
I wonder if someone has done a max continues load capacity test on the NCR BD cells? I think I have a few hanging around but I will have to figure out a constant 10A load...
 
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