Difference between revisions of "DIY E-Bike Battery"

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Revision as of 20:06, 27 July 2021

A project by User:Jpt4 and AVH to homebuild batteries their personal ebikes.


Contents

Cells

120 (total) LiFePO₄ 26650 cells purchased from Battery Hookup for the $228. Specifications:

  • Make/Model: K2 LFP26650E
  • Size: 26650
  • Voltage: 3.2
  • Capacity: 3.8 amp-hours (12.16 watt-hours)
  • Maximum Voltage: 3.65 (safe) 4.1 (maximum)
  • Minimum Voltage: 2.5 (safe) 2.0 (minimum)
  • Continuous Discharge Current: 12 amps
  • Maximum Discharge Current: 28 amps for 30 seconds
  • Recommended Charging Current: 3.8 amps

Packaging

The cells arrived in a tightly-fitting two-piece vacuum-formed plastic package that holds all the cells vertically in a 10x12 grid. The top of half of the package had some splits and cracks near one corner. The package, along with a desiccant pack, was in a thin plastic bag, zip-tied shut, in an exactly-fitting cardboard box.

Labels and Markings

Each cell is marked from the factory: 

  Li-Ion IFpR27/65
+ K2 Energy LP26650E-3800-21 -
  3.2V 3.8AH(12.16Wh)

Also, each cell has a serial number in a QR code near the negative terminal, (usually, but not always) on the side opposite the label. The dot-matrix printer that made the codes wasn't perfectly aligned, so many cells have codes that are slightly distorted and difficult to scan. Using the Barcode Scanner app, I found the codes could be scanned more reliably sideways.

To make it easier for us to keep track of the cells, the first time each cell was removed from the packaging, we gave them a three-digit number corresponding to the row and column they were from in the box. 000 is from the top-left, 009 is from the top-right, 110 is from the bottom-left, and 119 is from the bottom-right. The labels are written in permanent marker on the ample blank, white space on the cell wrappers, and underlined so that there is no ambiguity which way the number is supposed to be read.

Individual Cell Measurements

K2 26650 Li-Ion Cells
Serial Number Label Out-Of-The-Box Voltage
PH190223-132431 000 3.29
PH190223-132415 001 3.29
PH190223-132362 002 3.29
PH190223-132351 003 3.29
PH190223-132270 004 3.29
PH190223-132286 005 3.29
PH190223-132393 006 3.29
PH190223-132397 007 3.29
PH190223-132328 008 3.29
PH190223-132317 009 3.29
PH190223-132458 010 3.29
PH190223-132442 011 3.29
PH190223-132426 012 3.29
PH190223-132378 013 3.29
PH190223-132265 014 3.29
PH190223-132281 015 3.29
PH190223-132457 016 3.29
PH190223-132424 017 3.29
PH190223-132392 018 3.29
PH190223-132344 019 3.29
PH190223-132367 020 0.00 😭
PH190223-132350 021 3.29
PH190223-132334 022 3.29
PH190223-132233 023 3.29
PH190223-132269 024 3.29
PH190223-132462 025 3.29
PH190223-132398 026 3.19 🙁
PH190223-132414 027 3.29
PH190223-132413 028 3.29
PH190223-132333 029 3.29
PH190223-132394 030 3.29
PH190223-132361 031 3.29
PH190223-132345 032 3.29
PH190223-132329 033 3.29
PH190223-132296 034 3.29
PH190223-132280 035 3.29
PH190223-132409 036 3.29
PH190223-132425 037 3.29
PH190223-132440 038 3.29
PH190223-132360 039 3.29

Cell Testing

Out-Of-Box Voltage

When the package arrived, cell voltage was measured with the Ballantine 3028A bench multimeter.

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