Planning: Using holders for cells vs no holders - 18650 24v pack for mobility device

deswong

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Joined
Jan 20, 2021
Messages
22
Question for the group - Should I use holders for a 18650 24v LiPO battery pack or not?

I have built some packs for e-bikes in the past but due to space I simply pack them tightly and then spot weld them together. No fuses per cell.

Looking to replace some of the SLA batteries that I am using in a mobility scooter and electric wheelchair, both are 24V devices. Looking to build one to be equivalent of or greater capacity of 15Ah first up for the mobility scooter, then the big one is the electric wheelchair, stock is 50Ah SLA which will take a while to build!

Planning to use a Daly 7s LiPo BMS with these setups, Bluetooth for info/setup, set max to 4.1v per cell, and then having to mod a 7s LiPo charger to charge based on that.

Since joining this group and having over 1000 18650 cells to now sort out and determine what ones I will use for the pack, I have been thinking if there is another practical reason for using the standard 18650 holders that I am seeing people use.

Example image: https://secondlifestorage.com/index.php?attachments/image_vuzozr-jpg.19309/

I am guessing that the advantage is that the cells are air-gapped - similar to one I have found with the Ego 56v batteries, which means that if one cell gets excessively hot, the others are not affected as much. I am also thinking that you could take out a faulty cell easier if you find one that requires replacement? (Dreading this bit so planning carefully and working out the best matched cells to do this with!)

Are there any other advantages? I have space to do this in these devices, and however means that I cannot pack them with more power with the gaps.
 

Wolf

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Sep 25, 2018
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1,427
which means that if one cell gets excessively hot, the others are not affected as much
In all technicality if your cells are carefully tested and checked you should not have an "excessively hot" cell.
With all the information on cell testing that is available on this board there is no reason anyone should be putting a battery together that may even remotely include a "hot" cell. Careful selection and proper building technique should give you a reliable battery that is sized to your requirements and perform without incident for a reasonable time frame. As far as mobility batteries goes, one of the important things to consider is vibration and shock. In my opinion sturdy cell holders are a must and good spot welding a necessity. Additionally any form of vibration dampening would be a good idea also.
Wolf
 

OffGridInTheCity

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Joined
Dec 15, 2018
Messages
1,522
For me, they serve as a simple 'structural' component for a 100p or larger (as apposed to 20p). Using these with twist-ties create a physically hardy unit. This in turn makes it pretty easy to do bus-bars or spot-weld. In addition, you can actually replace individual cells that go bad by popping them thru and pushing in replacements. I've tried a few smaller batteries where I just taped them together... but round cells taped or glued together are still a bit of work no matter what you do. :)
 
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