UPGRADE BATTERY
My objective was increase the autonomy at least at 3h, to do that I needed +/- 1 KWh accumulated.
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1 Kwh is a lot of energy and potentialty dangerous, to reduce the risck and increas the life of cells I dived in two pack and weld a fuse each cells.
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Battery--> 2 pack whit 2 BMS, 7P7S 21700 cells 3.7V 3.27 Ah TOTAL 1185.80 Wh
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CELL
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After a logn serch I chose Samsun INR21700-33J because is the cells mounted on Tesla, and they have best value/cost.
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Pay attention! Difficult to spot weld, aluminum top
I bought single tag +0.15€, bottom pole is normal to weld.
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Samsung INR21700-33J 3270mAh - 6.4A - Single Tag (datasheet)
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DATA:
Capacity: 3270mAh
Rated Voltage 3.6V - 3.7V
Charging cycle termination voltage 4.20V ± 0.05V
max discharge current: 6.4A
Do not discharge deeper than 2.5V
Plus pool: Flat top
Chemistry: Li-ion
Weight: 62.8g
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Accord the datasheet, max discarge is 6.4A, at 0.5C (1.6A) the efficency of cell is 95%, enough to feed the engine.
The dpv adsorb from 200W to 800W so the cells work from 90% to 100% of their capacity (from 0.2C to 1C).
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Absortion of DPV (out of water)
To balance the cells:
I charged all and I storage and wait 10 days, then I checked the voltage (I suggest to write the voltage on battery to make easier the grouping) and divided and grouped by same voltage
gorup of 4.18V, 4.17V, 4.15V ecc.
BOM:
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-98 CELLS 21700
-4 CELLS HEADER
-2 BMS 7S 30A
-NIKEL STRIPS
-2 FUSE 30A
-POLIESTER RESIN 2KG (OPTIONAL)
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Solder work finished!
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The eletric scheme (download file for easyeda editor), this project is one module use 7 cells on series and 7 parallel and one bms, I made two module and parallel conected.
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To increase the safety I sealed by poliester resin.
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Blog di tecnologia ed elettronica subacquea
Augusto Pavan
It's better to be on the boat wishing you were in the water than
in the water wishing you were on the boat.