diMy Powerwall

mayson14

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My high tech rubber band setup.. until my 18650 holders show up..

Capacity testing every cell is going to take a very long time
image_jgmclm.jpg
 

daromer

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Note that if you dont et proper contact your readings may be off by several %.
 

mayson14

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daromer said:
Note that if you dont et proper contact your readings may be off by several %.

good to know.. im actually just charging this one. i wont do capacity tests until i get a proper setup.
 
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I'm not sure if it affects readings or not, but before I got cell holders I was using magnets.

Just soldered a small bit of nickel strip (recycled out of a pack) on end of wire, put that against the terminals and held it in place with a small rare earth magnet. The magnet never touched the cell. It worked really well, except on some Moli cells which seemed to have a non-attractive positive terminal.

Might provide better contact then rubber bands.
 

daromer

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Yeah proper magnets generally hold better in my experience. I have used clamps or a vice when testing like that so i know i have good contact :)
 

daromer

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Coool!
 

Alec_J

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I got two of the hover board packs this week. Man what a nightmare to disassemble! You have your work cut out for you! Good cells though.
 

mayson14

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Alec_J said:
I got two of the hover board packs this week. Man what a nightmare to disassemble! You have your work cut out for you! Good cells though.
It's not fun. But I found some help. Almost done!

Cleaning them and getting the glue off is the worst part. Im about over that.. I have a pack design in mind that might hide all the cells anyway.. stay tuned!
 

mayson14

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Im working on sizing my bus wires.. can you guys help me with the load on each pack? 14s70p, i will probably have a 4kw inverter. What kind of amperage could each pack see?
 

daromer

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On 14s and 4kw. Is it 4kw max? If not you need to calculate base don max current.

14*3.7=51,8

4000/51,8 = 77A

Thats just above 1A per cell. On my pack that is designed per basis MAX 1A per cell and 80A per pack i have 6*2.5mm2 copper wires twisted together. They should easily take the load without any larger loss. Reason for 2.5mm2 is because thats easy to find here for scrap value.

This is how i make them:
 

Korishan

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4000W/48V = 83A
83A / 70Cell = 1.186A/cell

I think I got my math right there. If that is correct, I would recommend going up in P size. 100p would make it .83A/Cell, and 120p would be .69A/Cell



Daromer beat me to it. :p but we kinda came close to the same amp/cell based on what you gave. 1A/cell is kinda the high end of what you want to pull.
 

mayson14

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I have access to a lot of cool stuff. This solid copper wire is #8 which I think is rated for 40amps. It seems too thick to double up but I could try it
image_tbovkw.jpg
 

Korishan

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Wish I had access to kind of wire! :)
 

mayson14

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I could up the pack size... would need to buy more cells though. Maybe i'll shoot for 80P
 

Korishan

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Or at least make your packs expandable so you can add more in parallel as you get more batches in. That was each time you add a layer of parallel, you drop the A/cell values
 

mayson14

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My wire guy says this solid copper is good for 95amps. Plus with two runs of it, it should only need to carry half the load.. just need to make sure my bus connection at the end can carry the full load..

Still brain storming design ideas
image_avytbi.jpg
 

mayson14

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what happens during discharge if one of the packs is a smaller capacity. For example (not that i plan on doing this) if you had 13s80p and the 14th in the series was only 40p? does that pack pull less amperage than the others so they all fall evenly?
 
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