Difference between revisions of "DIY E-Bike Battery"

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(→‎Individual Cell Measurements: added out-of-the-box voltage measurements for Row 03)
(→‎Individual Cell Measurements: added capacity measurements!)
 
(22 intermediate revisions by one user not shown)
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−
A project by [[User:Jpt4]] and [[User:Avh.on1|AVH]] to homebuild batteries their personal ebikes.
+
A project by [[User:Jpt4|Jpt4]] and [[User:Avh.on1|AVH]] to homebuild batteries for their personal ebikes.
  
  
 
== Cells ==
 
== Cells ==
−
120 (total) LiFePO₄ 26650 cells purchased from [https://batteryhookup.com/products/full-case-of-120-k2-26650-3800mah-lifepo4-cells Battery Hookup] for the $228. Specifications:
+
120 (total) LiFePO₄ 26650 cells purchased from [https://batteryhookup.com/products/full-case-of-120-k2-26650-3800mah-lifepo4-cells Battery Hookup] for the $228. Their specifications are as follows:
  
 
* Make/Model: K2 LFP26650E
 
* Make/Model: K2 LFP26650E
Line 26: Line 26:
 
   3.2V 3.8AH(12.16Wh)
 
   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 [https://f-droid.org/en/packages/com.google.zxing.client.android/ Barcode Scanner] app, I found the codes could be scanned more reliably sideways.
+
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 [https://f-droid.org/en/packages/com.google.zxing.client.android/ Barcode Scanner] app, the codes could be scanned more reliably sideways, or at not-quite-90-degree angles.
  
−
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.
+
To make it easier for us to keep track of the cells, the first time each cell was removed from the packaging, it was given 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 ===
 
=== Individual Cell Measurements ===
  
−
{| class="wikitable"
+
{| class="wikitable" style="text-align: right;"
 
|+ K2 26650 Li-Ion Cells
 
|+ K2 26650 Li-Ion Cells
 
! scope="col"| Serial Number
 
! scope="col"| Serial Number
 
! scope="col"| Label
 
! scope="col"| Label
 
! scope="col"| Out-Of-The-Box Voltage
 
! scope="col"| Out-Of-The-Box Voltage
 +
! scope="col"| Self-Discharge Voltage
 +
! scope="col"| Capacity (watt-hours)
 +
! scope="col"| Remarks <!-- This column should be right-most. -->
 
<!-- ================ START OF ROW 00 ================ -->
 
<!-- ================ START OF ROW 00 ================ -->
 
|-
 
|-
Line 42: Line 45:
 
| 000
 
| 000
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.682
 
|-
 
|-
 
| PH190223-132415
 
| PH190223-132415
 
| 001
 
| 001
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.770
 
|-
 
|-
 
| PH190223-132362
 
| PH190223-132362
 
| 002
 
| 002
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.808
 
|-
 
|-
 
| PH190223-132351
 
| PH190223-132351
 
| 003
 
| 003
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.898
 
|-
 
|-
 
| PH190223-132270
 
| PH190223-132270
 
| 004
 
| 004
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.932
 
|-
 
|-
 
| PH190223-132286
 
| PH190223-132286
 
| 005
 
| 005
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.876
 
|-
 
|-
 
| PH190223-132393
 
| PH190223-132393
 
| 006
 
| 006
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.802
 
|-
 
|-
 
| PH190223-132397
 
| PH190223-132397
 
| 007
 
| 007
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.945
 
|-
 
|-
 
| PH190223-132328
 
| PH190223-132328
 
| 008
 
| 008
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.943
 
|-
 
|-
 
| PH190223-132317
 
| PH190223-132317
 
| 009
 
| 009
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.862
 
<!-- ================ START OF ROW 01 ================ -->
 
<!-- ================ START OF ROW 01 ================ -->
 
|-
 
|-
Line 83: Line 106:
 
| 010
 
| 010
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.824
 
|-
 
|-
 
| PH190223-132442
 
| PH190223-132442
 
| 011
 
| 011
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.835
 
|-
 
|-
 
| PH190223-132426
 
| PH190223-132426
 
| 012
 
| 012
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.908
 
|-
 
|-
 
| PH190223-132378
 
| PH190223-132378
 
| 013
 
| 013
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.915
 
|-
 
|-
 
| PH190223-132265
 
| PH190223-132265
 
| 014
 
| 014
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.880
 
|-
 
|-
 
| PH190223-132281
 
| PH190223-132281
 
| 015
 
| 015
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.873
 
|-
 
|-
 
| PH190223-132457
 
| PH190223-132457
 
| 016
 
| 016
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.876
 
|-
 
|-
 
| PH190223-132424
 
| PH190223-132424
 
| 017
 
| 017
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.640
 
|-
 
|-
 
| PH190223-132392
 
| PH190223-132392
 
| 018
 
| 018
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.710
 
|-
 
|-
 
| PH190223-132344
 
| PH190223-132344
 
| 019
 
| 019
 
| 3.29
 
| 3.29
−
<!-- ================ START OF ROW 00 ================ -->
+
| 3.33
 +
| 10.737
 +
<!-- ================ START OF ROW 02 ================ -->
 
|-
 
|-
 
| PH190223-132367
 
| PH190223-132367
 
| 020
 
| 020
−
| 0.00 😭
+
| 0.00
 +
| 3.21
 +
| 8.886
 
|-
 
|-
 
| PH190223-132350
 
| PH190223-132350
 
| 021
 
| 021
 
| 3.29
 
| 3.29
 +
| 3.34
 +
| 10.678
 
|-
 
|-
 
| PH190223-132334
 
| PH190223-132334
 
| 022
 
| 022
 
| 3.29
 
| 3.29
 +
| 3.34
 +
| 10.845
 
|-
 
|-
 
| PH190223-132233
 
| PH190223-132233
 
| 023
 
| 023
 
| 3.29
 
| 3.29
 +
| 3.34
 +
| 10.792
 
|-
 
|-
 
| PH190223-132269
 
| PH190223-132269
 
| 024
 
| 024
 
| 3.29
 
| 3.29
 +
| 3.34
 +
| 10.758
 
|-
 
|-
 
| PH190223-132462
 
| PH190223-132462
 
| 025
 
| 025
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.813
 
|-
 
|-
 
| PH190223-132398
 
| PH190223-132398
 
| 026
 
| 026
−
| 3.19 🙁
+
| 3.19
 +
| 3.32
 +
| 9.369
 
|-
 
|-
 
| PH190223-132414
 
| PH190223-132414
 
| 027
 
| 027
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.759
 
|-
 
|-
 
| PH190223-132413
 
| PH190223-132413
 
| 028
 
| 028
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.788
 
|-
 
|-
 
| PH190223-132333
 
| PH190223-132333
 
| 029
 
| 029
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.646
 
<!-- ================ START OF ROW 03 ================ -->
 
<!-- ================ START OF ROW 03 ================ -->
 
|-
 
|-
Line 165: Line 228:
 
| 030
 
| 030
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.740
 
|-
 
|-
 
| PH190223-132361
 
| PH190223-132361
 
| 031
 
| 031
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.785
 
|-
 
|-
 
| PH190223-132345
 
| PH190223-132345
 
| 032
 
| 032
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.798
 
|-
 
|-
 
| PH190223-132329
 
| PH190223-132329
 
| 033
 
| 033
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.863
 
|-
 
|-
 
| PH190223-132296
 
| PH190223-132296
 
| 034
 
| 034
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.697
 
|-
 
|-
 
| PH190223-132280
 
| PH190223-132280
 
| 035
 
| 035
 
| 3.29
 
| 3.29
 +
| 3.34
 +
| 10.765
 
|-
 
|-
 
| PH190223-132409
 
| PH190223-132409
 
| 036
 
| 036
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.776
 
|-
 
|-
 
| PH190223-132425
 
| PH190223-132425
 
| 037
 
| 037
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.696
 
|-
 
|-
 
| PH190223-132440
 
| PH190223-132440
 
| 038
 
| 038
 
| 3.29
 
| 3.29
 +
| 3.33
 +
| 10.765
 
|-
 
|-
 
| PH190223-132360
 
| PH190223-132360
 
| 039
 
| 039
 
| 3.29
 
| 3.29
 +
| 3.32
 +
| 10.744
 +
<!-- ================ START OF ROW 04 ================ -->
 +
|-
 +
| PH190223-134729
 +
| 040
 +
| 3.29
 +
| 3.33
 +
| 10.620
 +
|-
 +
| PH190223-134648
 +
| 041
 +
| 3.29
 +
| 3.33
 +
| 10.757
 +
|-
 +
| PH190223-134519
 +
| 042
 +
| 3.29
 +
| 3.33
 +
| 10.762
 +
|-
 +
| PH120223-134644
 +
| 043
 +
| 3.29
 +
| 3.33
 +
| 10.798
 +
|-
 +
| PH190223-134515
 +
| 044
 +
| 3.29
 +
| 3.33
 +
| 10.669
 +
|-
 +
| PH190223-134691
 +
| 045
 +
| 3.29
 +
| 3.33
 +
| 10.822
 +
|-
 +
| PH190223-134713
 +
| 046
 +
| 3.29
 +
| 3.33
 +
| 10.874
 +
|-
 +
| PH190223-134628
 +
| 047
 +
| 3.29
 +
| 3.33
 +
| 11.145
 +
|-
 +
| PH190223-134632
 +
| 048
 +
| 3.29
 +
| 3.33
 +
| 11.249
 +
|-
 +
| PH190223-134760
 +
| 049
 +
| 3.29
 +
| 3.33
 +
| 10.829
 +
<!-- ================ START OF ROW 05 ================ -->
 +
|-
 +
| PH190223-134552
 +
| 050
 +
| 3.29
 +
| 3.33
 +
| 10.393
 +
|-
 +
| PH190223-134712
 +
| 051
 +
| 3.29
 +
| 3.33
 +
| 10.558
 +
|-
 +
| PH190223-134631
 +
| 052
 +
| 3.29
 +
| 3.33
 +
| 10.480
 +
|-
 +
| PH190223-134708
 +
| 053
 +
| 3.29
 +
| 3.33
 +
| 10.497
 +
|-
 +
| PH190223-134595
 +
| 054
 +
| 3.29
 +
| 3.33
 +
| 10.558
 +
|-
 +
| PH190223-134755
 +
| 055
 +
| 3.29
 +
| 3.33
 +
| 10.590
 +
|-
 +
| PH190223-134536
 +
| 056
 +
| 3.29
 +
| 3.33
 +
| 10.520
 +
|-
 +
| PH190223-134692
 +
| 057
 +
| 3.29
 +
| 3.33
 +
| 10.628
 +
|-
 +
| PH190223-134696
 +
| 058
 +
| 3.29
 +
| 3.33
 +
| 10.599
 +
|-
 +
| PH190223-134599
 +
| 059
 +
| 3.29
 +
| 3.33
 +
| 10.622
 +
<!-- ================ START OF ROW 06 ================ -->
 +
|-
 +
| PH190223-134756
 +
| 060
 +
| 3.29
 +
| 3.38
 +
| 10.739
 +
|-
 +
| PH190223-134675
 +
| 061
 +
| 3.29
 +
| 3.33
 +
| 10.715
 +
|-
 +
| PH190223-134697
 +
| 062
 +
| 3.29
 +
| 3.33
 +
| 10.767
 +
|-
 +
| PH190223-134584
 +
| 063
 +
| 3.29
 +
| 3.33
 +
| 10.809
 +
|-
 +
| PH190223-134744
 +
| 064
 +
| 3.29
 +
| 3.33
 +
| 10.879
 +
|-
 +
| PH190223-134596
 +
| 065
 +
| 3.29
 +
| 3.33
 +
| 10.633
 +
|-
 +
| PH190223-134740
 +
| 066
 +
| 3.29
 +
| 3.33
 +
| 10.695
 +
|-
 +
| PH190223-134643
 +
| 067
 +
| 3.29
 +
| 3.33
 +
| 11.051
 +
|-
 +
| PH190223-134681
 +
| 068
 +
| 3.29
 +
| 3.33
 +
| 10.863
 +
|-
 +
| PH190223-134568
 +
| 069
 +
| 3.29
 +
| 3.33
 +
| 10.842
 +
<!-- ================ START OF ROW 07 ================ -->
 +
|-
 +
| PH190223-134579
 +
| 070
 +
| 3.29
 +
| 3.38
 +
| 10.666
 +
|-
 +
| PH190223-134739
 +
| 071
 +
| 3.29
 +
| 3.33
 +
| 10.820
 +
|-
 +
| PH190223-134761
 +
| 072
 +
| 3.29
 +
| 3.33
 +
| 10.769
 +
|-
 +
| PH190223-134680
 +
| 073
 +
| 3.29
 +
| 3.33
 +
| 10.719
 +
|-
 +
| PH190223-134551
 +
| 074
 +
| 3.29
 +
| 3.33
 +
| 10.741
 +
|-
 +
| PH190223-134676
 +
| 075
 +
| 3.29
 +
| 3.33
 +
| 10.765
 +
|-
 +
| PH190223-134563
 +
| 076
 +
| 0.65
 +
| 3.33
 +
| 10.773
 +
|-
 +
| PH190223-134723
 +
| 077
 +
| 3.29
 +
| 3.33
 +
| 10.813
 +
|-
 +
| PH190223-134745
 +
| 078
 +
| 3.29
 +
| 3.33
 +
| 10.811
 +
|-
 +
| PH190223-134664
 +
| 079
 +
| 3.29
 +
| 3.33
 +
| 10.754
 +
<!-- ================ START OF ROW 08 ================ -->
 +
|-
 +
| PH190223-134728
 +
| 080
 +
| 3.29
 +
| 3.33
 +
| 11.277
 +
|-
 +
| PH190223-134564
 +
| 081
 +
| 3.29
 +
| 3.33
 +
| 11.429
 +
|-
 +
| PH190223-134724
 +
| 082
 +
| 3.29
 +
| 3.33
 +
| 10.742
 +
|-
 +
| PH190223-134627
 +
| 083
 +
| 3.29
 +
| 3.33
 +
| 10.689
 +
|-
 +
| PH190223-132318
 +
| 084
 +
| 3.29
 +
| 3.33
 +
| 10.815
 +
|-
 +
| PH190223-132446
 +
| 085
 +
| 3.29
 +
| 3.33
 +
| 10.787
 +
|-
 +
| PH190223-132365
 +
| 086
 +
| 3.29
 +
| 3.33
 +
| 10.836
 +
|-
 +
| PH190223-134709
 +
| 087
 +
| 3.29
 +
| 3.33
 +
| 10.706
 +
|-
 +
| PH190223-134693
 +
| 088
 +
| 3.29
 +
| 3.33
 +
| 10.729
 +
|-
 +
| PH190223-132399
 +
| 089
 +
| 3.29
 +
| 3.33
 +
| 10.863
 +
<!-- ================ START OF ROW 09 ================ -->
 +
|-
 +
| PH190223-134535
 +
| 090
 +
| 3.29
 +
| 3.33
 +
| 10.736
 +
|-
 +
| PH190223-134660
 +
| 091
 +
| 3.29
 +
| 3.33
 +
| 10.719
 +
|-
 +
| PH190223-134531
 +
| 092
 +
| 3.29
 +
| 3.33
 +
| 10.742
 +
|-
 +
| PH190223-134707
 +
| 093
 +
| 3.29
 +
| 3.33
 +
| 10.785
 +
|-
 +
| PH190223-132382
 +
| 094
 +
| 3.29
 +
| 3.33
 +
| 10.732
 +
|-
 +
| PH190223-132301
 +
| 095
 +
| 3.29
 +
| 3.33
 +
| 10.804
 +
|-
 +
| PH190223-132445
 +
| 096
 +
| 3.29
 +
| 3.33
 +
| 10.636
 +
|-
 +
| PH190223-134516
 +
| 097
 +
| 3.29
 +
| 3.33
 +
| 10.610
 +
|-
 +
| PH190223134757
 +
| 098
 +
| 3.29
 +
| 3.32
 +
| 10.635
 +
|-
 +
| PH190223-132223
 +
| 099
 +
| 3.29
 +
| 3.40
 +
| 10.686
 +
<!-- ================ START OF ROW 10 ================ -->
 +
|-
 +
| PH190223-132441
 +
| 100
 +
| 3.29
 +
| 3.33
 +
| 10.723
 +
|-
 +
| PH190223-132376
 +
| 101
 +
| 3.29
 +
| 3.32
 +
| 10.736
 +
|-
 +
| PH190223-132349
 +
| 102
 +
| 3.24
 +
| 3.32
 +
| 10.813
 +
|-
 +
| PH190223-132430
 +
| 103
 +
| 3.29
 +
| 3.36
 +
| 10.786
 +
|-
 +
| PH190223-132297
 +
| 104
 +
| 3.29
 +
| 3.32
 +
| 10.668
 +
|-
 +
| PH190223-132302
 +
| 105
 +
| 3.29
 +
| 3.33
 +
| 10.730
 +
|-
 +
| PH190223-134521
 +
| 106
 +
| 3.29
 +
| 3.33
 +
| 10.600
 +
|-
 +
| PH190223-134762
 +
| 107
 +
| 3.29
 +
| 3.33
 +
| 10.628
 +
|-
 +
| PH190223-132410
 +
| 108
 +
| 3.29
 +
| 3.33
 +
| 10.682
 +
|-
 +
| PH190223-132383
 +
| 109
 +
| 3.29
 +
| 3.33
 +
| 10.619
 +
<!-- ================ START OF ROW 11 ================ -->
 +
|-
 +
| PH190223-132312
 +
| 110
 +
| 3.28
 +
| 3.33
 +
| 10.486
 +
|-
 +
| PH190223-132456
 +
| 111
 +
| 3.29
 +
| 3.34
 +
| 10.401
 +
|-
 +
| PH190223-132429
 +
| 112
 +
| 3.29
 +
| 3.34
 +
| 10.522
 +
|-
 +
| PH190223-132285
 +
| 113
 +
| 3.24
 +
| 3.32
 +
| 11.400
 +
|-
 +
| PH190223-132377
 +
| 114
 +
| 3.29
 +
| 3.33
 +
| 14.682
 +
|-
 +
| PH190223-132366
 +
| 115
 +
| 3.29
 +
| 3.32
 +
| 10.532
 +
|-
 +
| PH190223-134633
 +
| 116
 +
| 3.29
 +
| 3.33
 +
| 10.617
 +
|-
 +
| PH190223-134585
 +
| 117
 +
| 3.29
 +
| 3.33
 +
| 10.706
 +
|-
 +
| PH190223-132218
 +
| 118
 +
| 3.29
 +
| 3.33
 +
| 10.610
 +
| Slightly torn wrapper
 +
|-
 +
| PH190223-132447
 +
| 119
 +
| 3.29
 +
| 3.32
 +
| 8.131
 +
 
|}
 
|}
  
Line 207: Line 780:
 
==== Out-Of-Box Voltage ====
 
==== Out-Of-Box Voltage ====
  
−
When the package arrived, cell voltage was measured with the [[Ballantine 3028A bench multimeter]].
+
When the package arrived, each cell's voltage was measured with the [[Ballantine 3028A | bench multimeter]]. (Also, its QR code was scanned, and its label written on.)
 +
 
 +
==== First Charge ====
 +
 
 +
A custom 5-cell holder was made from wood and brass strips (26650 cell holders are wiedly expensive , given how cheap 18650 cell holders are) and plugged in to a [https://www.toolkitrc.com/m7 ToolkitRC M7], which was plugged in to the benchtop power supply. This setup was used to charge 5 cells at a time (24 times) to charge the cells to 3.65V, the maximum setting the M7 can charge LiFePO₄ cells to. Then, the cells were charged 2 at a time on a [https://www.nitecorestore.com/Nitecore-D2-DigiCharger-p/chg-nite-d2.htm NiteCore Digicharger D2] to 3.70V.
 +
 
 +
==== Self-Discharge ====
 +
 
 +
This unintentional test was the result of effectively shelving the project for 16 months after the cells were charged. Cells with greater self-discharge (bad) will show lower voltages; cells with voltages closer to 3.65V have low self-discharge. Voltages were measures the same way out-of-box voltage was measured.
 +
 
 +
The results of this test were very encouraging. The cells held a much more consistent voltage than they had had out of the box, even the ones that had arrived severely discharged. This bodes well for their long-term performance in a battery.

Latest revision as of 20:19, 21 September 2023

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


Contents

[edit] Cells

120 (total) LiFePO₄ 26650 cells purchased from Battery Hookup for the $228. Their specifications are as follows:

  • 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

[edit] 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.

[edit] 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, the codes could be scanned more reliably sideways, or at not-quite-90-degree angles.

To make it easier for us to keep track of the cells, the first time each cell was removed from the packaging, it was given 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.

[edit] Individual Cell Measurements

K2 26650 Li-Ion Cells
Serial Number Label Out-Of-The-Box Voltage Self-Discharge Voltage Capacity (watt-hours) Remarks
PH190223-132431 000 3.29 3.33 10.682
PH190223-132415 001 3.29 3.33 10.770
PH190223-132362 002 3.29 3.33 10.808
PH190223-132351 003 3.29 3.33 10.898
PH190223-132270 004 3.29 3.33 10.932
PH190223-132286 005 3.29 3.33 10.876
PH190223-132393 006 3.29 3.33 10.802
PH190223-132397 007 3.29 3.33 10.945
PH190223-132328 008 3.29 3.33 10.943
PH190223-132317 009 3.29 3.33 10.862
PH190223-132458 010 3.29 3.33 10.824
PH190223-132442 011 3.29 3.33 10.835
PH190223-132426 012 3.29 3.33 10.908
PH190223-132378 013 3.29 3.33 10.915
PH190223-132265 014 3.29 3.33 10.880
PH190223-132281 015 3.29 3.33 10.873
PH190223-132457 016 3.29 3.33 10.876
PH190223-132424 017 3.29 3.33 10.640
PH190223-132392 018 3.29 3.33 10.710
PH190223-132344 019 3.29 3.33 10.737
PH190223-132367 020 0.00 3.21 8.886
PH190223-132350 021 3.29 3.34 10.678
PH190223-132334 022 3.29 3.34 10.845
PH190223-132233 023 3.29 3.34 10.792
PH190223-132269 024 3.29 3.34 10.758
PH190223-132462 025 3.29 3.33 10.813
PH190223-132398 026 3.19 3.32 9.369
PH190223-132414 027 3.29 3.33 10.759
PH190223-132413 028 3.29 3.33 10.788
PH190223-132333 029 3.29 3.33 10.646
PH190223-132394 030 3.29 3.33 10.740
PH190223-132361 031 3.29 3.33 10.785
PH190223-132345 032 3.29 3.33 10.798
PH190223-132329 033 3.29 3.33 10.863
PH190223-132296 034 3.29 3.33 10.697
PH190223-132280 035 3.29 3.34 10.765
PH190223-132409 036 3.29 3.33 10.776
PH190223-132425 037 3.29 3.33 10.696
PH190223-132440 038 3.29 3.33 10.765
PH190223-132360 039 3.29 3.32 10.744
PH190223-134729 040 3.29 3.33 10.620
PH190223-134648 041 3.29 3.33 10.757
PH190223-134519 042 3.29 3.33 10.762
PH120223-134644 043 3.29 3.33 10.798
PH190223-134515 044 3.29 3.33 10.669
PH190223-134691 045 3.29 3.33 10.822
PH190223-134713 046 3.29 3.33 10.874
PH190223-134628 047 3.29 3.33 11.145
PH190223-134632 048 3.29 3.33 11.249
PH190223-134760 049 3.29 3.33 10.829
PH190223-134552 050 3.29 3.33 10.393
PH190223-134712 051 3.29 3.33 10.558
PH190223-134631 052 3.29 3.33 10.480
PH190223-134708 053 3.29 3.33 10.497
PH190223-134595 054 3.29 3.33 10.558
PH190223-134755 055 3.29 3.33 10.590
PH190223-134536 056 3.29 3.33 10.520
PH190223-134692 057 3.29 3.33 10.628
PH190223-134696 058 3.29 3.33 10.599
PH190223-134599 059 3.29 3.33 10.622
PH190223-134756 060 3.29 3.38 10.739
PH190223-134675 061 3.29 3.33 10.715
PH190223-134697 062 3.29 3.33 10.767
PH190223-134584 063 3.29 3.33 10.809
PH190223-134744 064 3.29 3.33 10.879
PH190223-134596 065 3.29 3.33 10.633
PH190223-134740 066 3.29 3.33 10.695
PH190223-134643 067 3.29 3.33 11.051
PH190223-134681 068 3.29 3.33 10.863
PH190223-134568 069 3.29 3.33 10.842
PH190223-134579 070 3.29 3.38 10.666
PH190223-134739 071 3.29 3.33 10.820
PH190223-134761 072 3.29 3.33 10.769
PH190223-134680 073 3.29 3.33 10.719
PH190223-134551 074 3.29 3.33 10.741
PH190223-134676 075 3.29 3.33 10.765
PH190223-134563 076 0.65 3.33 10.773
PH190223-134723 077 3.29 3.33 10.813
PH190223-134745 078 3.29 3.33 10.811
PH190223-134664 079 3.29 3.33 10.754
PH190223-134728 080 3.29 3.33 11.277
PH190223-134564 081 3.29 3.33 11.429
PH190223-134724 082 3.29 3.33 10.742
PH190223-134627 083 3.29 3.33 10.689
PH190223-132318 084 3.29 3.33 10.815
PH190223-132446 085 3.29 3.33 10.787
PH190223-132365 086 3.29 3.33 10.836
PH190223-134709 087 3.29 3.33 10.706
PH190223-134693 088 3.29 3.33 10.729
PH190223-132399 089 3.29 3.33 10.863
PH190223-134535 090 3.29 3.33 10.736
PH190223-134660 091 3.29 3.33 10.719
PH190223-134531 092 3.29 3.33 10.742
PH190223-134707 093 3.29 3.33 10.785
PH190223-132382 094 3.29 3.33 10.732
PH190223-132301 095 3.29 3.33 10.804
PH190223-132445 096 3.29 3.33 10.636
PH190223-134516 097 3.29 3.33 10.610
PH190223134757 098 3.29 3.32 10.635
PH190223-132223 099 3.29 3.40 10.686
PH190223-132441 100 3.29 3.33 10.723
PH190223-132376 101 3.29 3.32 10.736
PH190223-132349 102 3.24 3.32 10.813
PH190223-132430 103 3.29 3.36 10.786
PH190223-132297 104 3.29 3.32 10.668
PH190223-132302 105 3.29 3.33 10.730
PH190223-134521 106 3.29 3.33 10.600
PH190223-134762 107 3.29 3.33 10.628
PH190223-132410 108 3.29 3.33 10.682
PH190223-132383 109 3.29 3.33 10.619
PH190223-132312 110 3.28 3.33 10.486
PH190223-132456 111 3.29 3.34 10.401
PH190223-132429 112 3.29 3.34 10.522
PH190223-132285 113 3.24 3.32 11.400
PH190223-132377 114 3.29 3.33 14.682
PH190223-132366 115 3.29 3.32 10.532
PH190223-134633 116 3.29 3.33 10.617
PH190223-134585 117 3.29 3.33 10.706
PH190223-132218 118 3.29 3.33 10.610 Slightly torn wrapper
PH190223-132447 119 3.29 3.32 8.131

[edit] Cell Testing

[edit] Out-Of-Box Voltage

When the package arrived, each cell's voltage was measured with the bench multimeter. (Also, its QR code was scanned, and its label written on.)

[edit] First Charge

A custom 5-cell holder was made from wood and brass strips (26650 cell holders are wiedly expensive , given how cheap 18650 cell holders are) and plugged in to a ToolkitRC M7, which was plugged in to the benchtop power supply. This setup was used to charge 5 cells at a time (24 times) to charge the cells to 3.65V, the maximum setting the M7 can charge LiFePO₄ cells to. Then, the cells were charged 2 at a time on a NiteCore Digicharger D2 to 3.70V.

[edit] Self-Discharge

This unintentional test was the result of effectively shelving the project for 16 months after the cells were charged. Cells with greater self-discharge (bad) will show lower voltages; cells with voltages closer to 3.65V have low self-discharge. Voltages were measures the same way out-of-box voltage was measured.

The results of this test were very encouraging. The cells held a much more consistent voltage than they had had out of the box, even the ones that had arrived severely discharged. This bodes well for their long-term performance in a battery.

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