Detecting single cell reversals in long series batteries

Discussion in 'The Projects Forum' started by Mr. Mik, Oct 26, 2010.

  1. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Hello forum members! :)

    I'm new here and would like some help with a project that aims at developing a simple electronic Battery Management System (BMS) for NiMH serial batteries in an electric Vectrix scooter or other electric vehicles. I call it the IDeA for "Imbalance Detection Apparatus".

    The "IDeA" would have at least 2 separate functions:

    1) Warning the rider of battery imbalance when the stock system is unaware of this, by illuminating a warning light but not cutting power. The rider will have the choice to continue to use all power that the stock system provides, but at the expense of the reversing cell; this keeps the vehicle roadworthy for longer in case it occurs in dangerous traffic conditions.

    2) Automatically cut power during automated deep discharges once imbalance due to a single reversing cell is detected.

    The IDeA is supposed to compare battery segment voltages to each other and trigger the "Imbalance" response if a voltage difference of maybe 0.8V is detected between any two of them.


    The IDeA should run on the same 12V DC as the cooling impellers.


    The IDeAs output must be galvanically isolated from the battery to keep everything as safe as possible.


    Here is some background to help understand the problem to be solved:

    All the effort for BMS development seems to go into Lithium BMS at the moment; I cannot find any decent NiMH system (except maybe the Prius and Insight systems, but they are not easily adaptable).

    The cell voltage (of 1.2-1.5V) per NiMH cell means that the cell numbers are much higher than in comparable Lithium batteries. Any cell-level-BMS becomes expensive due to this large number of cells. And there may not be enough space in the batteries to install multiple per-cell-systems without interfering with the forced airflow usually needed for cooling NiMH batteries.

    It appears to me that the usual approach to NiMH battery management is to overcharge them at C/10 (or less) to equalise the cells. The more often this is done, the quicker the entire battery ages. But if the EQ charging is not done, then sooner or later cell reversal occurs during discharge. If the cell reversal goes undetected, then it will soon kill the affected cells and bring down the entire battery pack.

    Alternatively, the SOC (State of Charge) is kept in a relatively narrow band around the 50% SOC area most of the time, like 40%-60% SOC. My hypothesis for how this works is this: It allows some cells to fall behind in SOC until they are being cycled between maybe 10%-30% SOC, while the highest cells cycle around 70%-90% SOC. Because the self-discharge rate (SDCR) is higher at higher SOC, they drift apart until the SDCR of the low cells is so low (and that of the high-SOC cells so high) that the difference in SOC stabilises. The battery is then imbalanced, but no cell reversal occurs, because only a small part of the capacity is ever used.
    This approach might work well for hybrid vehicles, but if only such a small portion of the capacity is being accessed it restricts the range too severely for EV (electric vehicle) use.

    Lithium BMSystems need to monitor every cell because the cells suffer quite severe damage if they are discharged to deeply or if they are over-charged. Once the over-charge or over-discharge has occurred, it is generally too late for Lithium cells.

    But NiMH cells are much more resilient in this respect and I think that a system that detects the sudden drop by about 1.4V will prevent serious damage to the reversing cell - if the discharge is then stopped.

    The reversal of a single cell in a NiMH battery string should be the latest point at which the discharge is terminated. If the discharge continues for too long, particularly if at a high current rate, then the cell will become irreversibly damaged.

    Complicating all this is the fact that NiMH cell voltage is very dependent on discharge (or charge) current, SOC and temperature. It is very difficult - if not impossible - to reliably determine the remaining charge from the voltage of a NiMH cell.

    And occasional deep discharges are required in order to remove voltage depression effects from the cells and sometimes to synchronise the "Fuel gauge", which progressively gets out of sync with the real SOC if it only relies on coulomb counting.

    This graphs shows the voltage drop from a single reversing cell in a Vectrix 102s 30Ah NiMH battery pack. It is this small drop in pack voltage (at 12hrs:33min) that I want the IDeA to detect.

    [​IMG]

    Red curve: Pack voltage (x100)
    Blue curve: Current (x 1/10)
    X-axis: hrs:min:sec:msec

    So what you can see there is a drop in voltage from about 123V to 122V over a minute or so, under a current draw of about 1.1A .

    Done on the bench with a constant current discharge it is easy to spot.

    But under a, say, 200A current draw the battery voltage would immediately drop to about 105V. During on-road use, the constantly changing discharge currents (or charge from regenerative braking) make it impossible to spot such a small drop in voltage - unless one compares equal sub-strings to each other.

    That's where the IDeA (Imbalance Detection Apparatus) comes in!

    It compares the voltages of equal parts of the battery to each other, while they are experiencing identical charge and discharge currents. The cell temperatures would hopefully be similar enough to not introduce too much voltage difference between these sub-strings.

    For the Vectrix pack of 102 serial connected cells, three segments of 34 cells each might be the best option to implement the IDeA.

    Two segments of 51 cells would make it much more likely that a reversing cell occurs in each segment at the same time, making it invisible to the IDeA. Synchronous reversal of equal numbers of cells in 3 or 6 segments are much less likely, but monitoring six segments of 17 cells each involves a lot of dismantling and installation of cables and fuses close to live parts.

    The 3x34 cells option could be installed easily, because all the relevant cells are in the top layer (of three layers) in the battery.


    The work done so far is based on a circuit by G. La Rooy, Christchurch, New Zealand.

    described here: http://www.siliconchip.com.au/cms/A_30610/article.html and here: http://www.extremecircuits.net/2009/12/battery-equality-monitor-circuit.html

    This circuit was then extended to work for three battery segments by "Mikemitbike" here: http://visforvoltage.org/forum/9675...trix-battery-it-becomes-damaged#comment-54426

    I did then play around with resistor values to tweak it a bit so that transistors with a hFE of 50 can be used, but the simulation was otherwise already complete. It was made using the applet at http://www.falstad.com/circuit/

    Here is what it looks like:
    [​IMG]

    Unfortunately the applet does not seem to have opto-couplers to simulate with, so LED's take their place.
    Here is a schematic that shows it more clearly:
    [​IMG]

    To see the simulation in action, paste the code (coming in the next post because it exceeds the 10000 chracter limit!) into the "Import" window of the applet. You can also run this applet from your computer after downloading it. Then change the voltages of the three battery parts a little bit (right click on components and select "Edit") to see what happens (the LED's light up). I assume I will not be able to post a reply to this first post immediately, so in the meantime you can grab the code from this post: http://visforvoltage.org/forum/9675...trix-battery-it-becomes-damaged#comment-54490



    I have made a simulation to show how the IDeA part on the output side of the optocouplers will hopefully work with the rest of the Vectrix scooter:

    [​IMG]

    The code for this simulation will also have to follow in the next post due to character limits of the forum software.
    In the meantime you can grab it from here: http://visforvoltage.org/forum/9675...trix-battery-it-becomes-damaged#comment-54731

    I better stop here before the post becomes completely unreadable - if it is not already!

    I'll specify the questions I have in the next post. They mainly relate to the best approach for turning this from a simulation into a real prototype device....
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,696
    904
    I would like to see that verified in a fault situation, like you show. Do you have evidence it holds true under all discharge/charge scenarios?

    John
     
  3. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Here is the code to be pasted into the applet at: http://www.falstad.com/circuit/


    First, the code for the part of the circuit on the output side of the optocouplers:


    Code ( (Unknown Language)):
    1.  
    2. $ 1 5.0E-6 2.275989509352673 32 5.0 43
    3. t 224 240 256 240 0 1 -11.554883047560514 0.24839342266879083 100.0
    4. 178 416 384 416 432 0 1 0.2 -2.0654999999009103E-9 0.05 3390000.0 0.00922 1000.0
    5. 162 400 304 400 256 1 2.1024259 1.0 0.0 0.0
    6. r 400 304 400 352 0 910.0
    7. w 400 352 400 432 0
    8. w 464 208 400 208 0
    9. w 400 208 400 256 0
    10. w 384 208 400 208 0
    11. v 688 432 608 432 0 0 40.0 12.0 0.0 0.0 0.5
    12. v 880 224 880 160 0 0 40.0 135.0 0.0 0.0 0.5
    13. 178 864 432 864 480 0 1 0.2 0.03518515660907174 0.05 1000000.0 0.02 300.0
    14. d 560 432 560 368 1 0.805904783
    15. x 21 46 109 55 0 40 IDeA
    16. x 45 358 166 362 0 15 Optocouplers 1 - 4
    17. x 589 404 752 410 0 24 Key or Charger
    18. x 35 374 180 377 0 10 (closed if imbalance detected)
    19. x 910 220 1045 226 0 24 110-154VDC
    20. x 534 181 609 187 0 24 12VDC
    21. x 607 464 695 468 0 15 12VDC Stock
    22. v 576 144 528 144 0 0 40.0 12.0 0.0 0.0 0.5
    23. 178 624 64 624 144 0 1 0.2 -0.3552164188922481 0.05 1000000.0 0.02 380.0
    24. w 608 144 576 144 0
    25. w 624 64 672 64 0
    26. w 864 32 576 32 0
    27. w 576 32 576 64 0
    28. w 592 64 592 48 0
    29. w 592 48 704 48 0
    30. w 416 144 384 144 0
    31. w 368 384 256 384 0
    32. w 432 432 448 432 0
    33. w 384 384 384 368 0
    34. w 384 368 368 368 0
    35. w 368 208 384 208 0
    36. w 416 384 432 384 0
    37. w 432 384 432 160 0
    38. w 384 144 384 160 0
    39. w 384 160 432 160 0
    40. w 384 144 320 144 0
    41. x 330 106 442 110 0 15 Cooling Impellers
    42. w 320 144 272 144 0
    43. w 272 144 256 144 0
    44. x 648 382 686 385 0 10 ON/OFF
    45. x 365 456 432 461 0 20 Relay 1
    46. x 821 508 888 513 0 20 Relay 2
    47. x 623 23 989 27 0 15 (not needed - just simulating galvanic isolation by SMPS)
    48. s 624 368 704 368 0 0 false
    49. w 320 144 320 80 0
    50. w 528 80 528 208 0
    51. s 448 80 528 80 0 0 false
    52. w 464 208 528 208 0
    53. w 528 208 544 208 0
    54. w 576 208 672 208 0
    55. w 416 144 528 144 0
    56. w 544 208 576 208 0
    57. s 624 304 720 304 0 1 false
    58. w 864 320 864 400 0
    59. w 704 48 848 48 0
    60. w 848 48 848 448 0
    61. w 864 400 864 432 0
    62. w 848 448 848 480 0
    63. d 784 432 736 432 1 0.805904783
    64. w 816 432 784 432 0
    65. w 560 368 624 368 0
    66. w 816 368 704 368 0
    67. w 816 368 832 368 0
    68. w 736 432 688 432 0
    69. w 608 432 560 432 0
    70. w 832 432 832 368 0
    71. w 864 32 880 32 0
    72. w 880 32 880 160 0
    73. w 864 320 880 320 0
    74. w 880 320 880 224 0
    75. w 448 432 464 432 0
    76. w 816 240 816 432 0
    77. w 832 368 832 304 0
    78. x 910 192 1044 198 0 24 Main Battery
    79. x 575 269 739 273 0 15 Deep Discharge On/OFF
    80. x 577 284 738 288 0 15 or Parking Cooling Timer
    81. x 345 269 385 273 0 15 Dash-
    82. x 346 287 383 291 0 15 board
    83. x 351 303 380 307 0 15 LED
    84. w 672 208 816 208 0
    85. w 816 208 816 240 0
    86. w 608 304 624 304 0
    87. w 832 304 720 304 0
    88. w 816 208 816 64 0
    89. w 816 64 672 64 0
    90. x 639 180 793 186 0 24 ABCool SMPS
    91. x 471 97 509 100 0 10 ON/OFF
    92. w 368 368 304 368 0
    93. w 304 368 304 208 0
    94. w 304 208 368 208 0
    95. x 653 319 691 322 0 10 ON/OFF
    96. x 934 163 1006 169 0 24 Vectux
    97. x 554 26 621 31 0 20 Relay 3
    98. x 126 37 478 43 0 24 (Imbalance Detection Apparatus)
    99. s 64 176 112 176 0 1 false
    100. s 64 224 112 224 0 1 false
    101. s 64 272 112 272 0 1 false
    102. s 64 320 112 320 0 1 false
    103. w 48 176 64 176 0
    104. w 48 224 64 224 0
    105. w 48 272 64 272 0
    106. w 48 320 64 320 0
    107. r 320 80 384 80 0 1.5
    108. r 384 80 432 80 0 1.5
    109. w 432 80 448 80 0
    110. t 112 176 144 176 0 1 -11.456343502368767 0.09853954519174213 100.0
    111. t 112 224 144 224 0 1 -11.456343502368767 0.09853954519174213 100.0
    112. t 112 272 144 272 0 1 -11.456343502368767 0.09853954519174213 100.0
    113. t 112 320 144 320 0 1 -11.456343502368767 0.09853954519174213 100.0
    114. w 160 144 160 160 0
    115. w 160 160 144 160 0
    116. w 160 160 160 208 0
    117. w 160 208 144 208 0
    118. w 160 208 160 256 0
    119. w 160 256 144 256 0
    120. w 160 256 160 304 0
    121. w 160 304 144 304 0
    122. w 144 192 192 192 0
    123. w 192 192 192 240 0
    124. w 192 240 224 240 0
    125. w 144 240 192 240 0
    126. w 144 288 192 288 0
    127. w 192 288 192 240 0
    128. w 144 336 192 336 0
    129. w 192 336 192 288 0
    130. x 376 483 412 486 0 10 12V DC
    131. x 664 193 758 196 0 10 125V DC --> 12v DC
    132. x 834 531 876 534 0 10 250V DC
    133. x 472 455 523 460 0 20 Diode
    134. x 460 467 534 470 0 10 stops Stock 12V
    135. x 821 520 892 523 0 10 Normally Open
    136. x 356 471 433 474 0 10 Normally Closed
    137. d 496 432 496 368 1 0.805904783
    138. w 464 432 496 432 0
    139. w 496 368 496 304 0
    140. w 608 304 496 304 0
    141. x 470 499 519 502 0 10 on start-up
    142. x 445 487 556 490 0 10 due to driving Impellers
    143. 162 16 176 48 176 1 0.1 1.0 0.0 0.0
    144. 162 16 224 48 224 1 2.1024259 1.0 0.0 0.0
    145. 162 16 272 48 272 1 2.1024259 1.0 0.0 0.0
    146. 162 16 320 48 320 1 2.1024259 1.0 0.0 0.0
    147. w 16 144 16 176 0
    148. w 16 176 16 224 0
    149. w 16 224 16 272 0
    150. w 16 272 16 320 0
    151. x 67 343 116 346 0 10 Simulated
    152. x 476 477 517 480 0 10 overload
    153. w 256 224 256 144 0
    154. w 256 256 256 384 0
    155. w 256 144 160 144 0
    156. w 128 112 128 96 0
    157. w 128 96 112 96 0
    158. w 112 96 112 112 0
    159. w 112 112 96 112 0
    160. w 96 112 96 96 0
    161. w 96 96 80 96 0
    162. w 80 96 80 112 0
    163. w 80 112 64 112 0
    164. w 64 96 64 112 0
    165. w 64 96 48 96 0
    166. w 48 96 48 112 0
    167. w 48 112 32 112 0
    168. w 32 112 16 112 0
    169. w 16 112 16 144 0
    170. x 38 87 147 90 0 10 This wire does not exist
    171. x 49 129 135 132 0 10 in the real device!
    172. w 160 144 160 112 0
    173. w 128 112 144 112 0
    174. w 160 112 144 112 0
    175. w 960 336 960 320 0
    176.  

    Next, the code for the part of the circuit that is in contact with the up to 153V of the Vectrix battery on the input side of the optocouplers (The battery segments are set to 51.9V, 51V and 51V, so one LED/optocoupler is already ON):


    Code ( (Unknown Language)):
    1.  
    2. $ 1 5.0E-6 4.818269829109882 48 5.0 50
    3. v 848 256 848 160 0 0 40.0 51.9 0.0 0.0 0.5
    4. v 848 352 848 256 0 0 40.0 51.0 0.0 0.0 0.5
    5. w 352 160 272 160 0
    6. t 208 112 272 112 0 1 -23.28459012772871 0.6286731540496523 50.0
    7. t 96 160 160 160 0 1 -0.25321565946262226 0.643783895068311 50.0
    8. t 208 208 272 208 0 -1 50.25521623645125 -0.26832640048128104 50.0
    9. w 208 112 160 112 0
    10. w 160 144 160 112 0
    11. w 208 208 160 208 0
    12. w 160 208 160 176 0
    13. r 160 112 160 64 0 3300.0
    14. r 160 208 160 256 0 3300.0
    15. r 96 160 96 208 0 5900.0
    16. w 160 112 96 112 0
    17. w 160 208 96 208 0
    18. r 272 96 272 48 0 3300.0
    19. r 272 224 272 272 0 3300.0
    20. 162 272 0 272 48 1 1.18 1.0 0.0 0.0
    21. 162 272 272 272 320 1 1.18 1.0 0.0 0.0
    22. w 352 320 272 320 0
    23. w 352 0 272 0 0
    24. w 160 64 160 0 0
    25. w 160 0 272 0 0
    26. w 160 256 160 320 0
    27. w 160 320 272 320 0
    28. w 272 128 272 160 0
    29. w 272 192 272 160 0
    30. w 352 160 432 160 0
    31. w 432 160 544 160 0
    32. w 544 160 544 192 0
    33. 162 432 160 432 224 1 1.18 1.0 0.0 0.0
    34. r 432 224 432 272 0 3300.0
    35. t 480 288 432 288 0 1 -49.79248593413201 0.448118488677018 50.0
    36. v 848 448 848 352 0 0 40.0 51.0 0.0 0.0 0.5
    37. w 432 304 432 320 0
    38. w 352 320 432 320 0
    39. r 544 192 544 256 0 3300.0
    40. w 544 256 544 288 0
    41. w 480 288 544 288 0
    42. t 480 368 432 368 0 -1 49.79248593411766 -0.44811848868142334 50.0
    43. w 432 352 432 320 0
    44. r 432 384 432 432 0 3300.0
    45. t 576 336 544 336 0 1 -0.25254264597874965 0.6436943313796917 50.0
    46. w 544 288 544 320 0
    47. w 544 352 544 368 0
    48. w 544 368 480 368 0
    49. 162 432 432 432 480 1 1.18 1.0 0.0 0.0
    50. w 432 480 352 480 0
    51. w 432 480 544 480 0
    52. w 544 480 544 464 0
    53. r 544 464 544 400 0 3300.0
    54. w 544 400 544 368 0
    55. w 544 256 608 256 0
    56. w 544 400 608 400 0
    57. r 608 400 608 336 0 5900.0
    58. w 576 336 608 336 0
    59. w 432 160 432 112 0
    60. w 352 0 432 0 0
    61. w 432 0 432 48 0
    62. w 848 160 848 96 0
    63. w 848 448 848 512 0
    64. w 352 480 272 480 0
    65. w 272 480 272 448 0
    66. w 272 320 272 384 0
    67. r 432 48 432 112 0 3300.0
    68. r 272 384 272 448 0 3300.0
    69. x 929 321 999 327 0 24 To MC
    70. w 848 160 784 160 0
    71. s 736 352 784 352 0 0 false
    72. s 736 256 784 256 0 0 false
    73. s 736 160 784 160 0 0 false
    74. w 848 256 784 256 0
    75. w 848 352 784 352 0
    76. s 736 448 784 448 0 0 false
    77. w 848 448 784 448 0
    78. w 848 96 960 96 0
    79. w 960 96 960 288 0
    80. w 848 512 960 512 0
    81. w 960 512 960 336 0
    82. w 544 480 688 480 0
    83. w 688 480 736 448 0
    84. w 544 160 624 160 0
    85. w 160 320 160 512 0
    86. w 576 512 736 352 0
    87. w 160 512 576 512 0
    88. w 624 160 736 256 0
    89. w 688 160 736 160 0
    90. w 688 160 512 0 0
    91. w 432 0 512 0 0
    92. x 846 73 1000 79 0 24 Vectrix Battery
    93. x 725 504 822 510 0 24 Relais 4x
    94. 174 64 144 96 176 0 1240.0 0.5 Resistance
    95. 174 80 336 80 368 0 1000.0 0.5 Resistance
    96. 174 64 288 96 320 0 1000.0 0.5 Resistance
    97. w 64 144 64 112 0
    98. w 64 112 96 112 0
    99. 174 640 320 608 352 0 1240.0 0.5 Resistance
    100. w 640 320 640 256 0
    101. w 640 256 608 256 0
    102. o 15 64 0 291 89.89929842676084 0.028093530758362767 0 -1
    103. o 16 64 0 33 5.462437423415176E-5 6.991919901971428E-5 1 -1
    104. o 31 64 0 33 0.013409991983252661 6.704995991626331E-5 2 -1
    105. o 41 64 0 33 0.01953125 9.765625E-5 3 -1
    106. o 17 64 0 35 5.0 0.025 4 -1
    107.  


    Give it a go, the applet is very easy to use!
     
    Last edited by a moderator: Oct 28, 2010
  4. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    No, I have no evidence for all scenarios. There are too many possible scenarios - and I need to build the thing first!

    But what I have done is make multiple manual voltage measurements during the assessment of a used Vectrix battery, during charging and discharging. All the measurements have been consistent with my impression that it will work well - but I might of course be deluding myself! The details can be found in this post and the posts following it: http://visforvoltage.org/forum/8406-how-would-you-diagnose-and-restore-vectrix-battery#comment-54326

    Because I built a manual BMS to nurse my damaged Vectrix battery pack along, I have been able to measure the voltages of 15 individual cells as well as voltages of all modules of 8 or 9 cells in the battery under all charging and riding conditions for over 7000km of on-road use. See https://www.endless-sphere.com/forums/download/file.php?id=40868
    and https://www.endless-sphere.com/forums/viewtopic.php?f=14&t=6853&start=45#p281768
    The results from this are also consistent with my impression that even somewhat damaged (= capacity reduced) NiMH cells will hold remarkably similar voltages, including under load - until they suddenly go over the knee in the discharge curve.

    So, as far as I can, I have verified that it should work. That does however only relate to the measurement and comparison of the three battery segment voltages, not to the IDeA device. That unfortunately only exists as schematics, simulations and loose parts waiting for the soldering iron!
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You might find this thread relevant:
    http://forum.allaboutcircuits.com/showthread.php?t=35567
    It involves a discussion of monitoring multiple batteries wired in series using OptoMOS relays to select which battery will be tested.

    You're using relays in your circuits. Relay coils use a good bit of power when they are energized, and don't last forever.
     
  6. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Thank you, I had a read of the thread and found it interesting, although much of it was too complicated for me. If I understand it correctly, the relays (optical) you suggested for that circuit are used to switch individual cells in or out so their actual voltage can be measured without shorting the cells to other parts of the battery.

    This is however not an issue with the relays in the circuit I am working on. They can be switched on or off at any time without any shorts occurring in the battery as a result. This circuit does not measure voltage of the three battery parts, it only compares them to each other. In normal operation the voltages of the three battery segments would range from 34V each to 51V each. Whenever there is a difference of more than 0.5-1V between any of the three segments, one or two of the 4 LED's (or optocouplers) will light up.
    The optocoupler output can then be used to trigger whatever action is wanted: To light a warning LED or shut down an automated discharge.

    Having read the thread you recommended, I now wonder if solid state relays could be used instead of optocouplers! If I understand it correctly, then it's an "all-or-nothing" response when an SSR is used, versus a gradual rise in output current for an optocoupler (depending on it's CTR = Current Transfer Ratio).

    Am I right that an optical relay (= SSR?) has no CTR? Just an all-or-nothing response?

    As far as deterioration due to frequent mechanical switching is concerned, that should not be an issue in the IDeA design, either. The relays would only be switching a few times each day: When turning the scooter (or other EV) on and off; and very rarely when the first reversing cell is detected during the automated deep discharge - maybe once every three months. That should be OK for decades or centuries of use.

    Vibration due to on-road use is an issue where SSR's have a big advantage. However, the only "action" that the IDeA system takes during riding is to light a warning LED if imbalance is detected. That could happen if some of the poles of the relays between the 4 battery tabs and the transistor circuit were to briefly open due to vibration. I imagine the red LED would occasionally blink when riding over rough spots on the road. That would be easily distinguishable from the throttle -dependent state of the warning LED when it is due to a cell reversal.

    I do not know how to choose the appropriate voltage rating for the relays (optical or mechanical) between the battery tabs and the transistor circuit. Do I need to use >150V rated because of the max 153V of the battery, or is >51V enough because that is the maximum difference between one tab and the next?

    I found mechanical relays with 220VDC contact ratings, but those SSR's that I could find with a high contact voltage rating are very expensive.

    Would the relays (Avago ASSR-1228-302E http://au.element14.com/avago-techn...2a-60v-dip8-smd/dp/1708434?Ntt=ASSR-1228-302E ) discussed in the LED-Bargraph LM3914 thread be used for the IDeA circuit? They have a 60V contact rating.
    Could they be used for the battery tab switching AND also to replace the optocouplers?

    Regarding the energy consumption by the relays vs. SSR's:
    I think the energy consumption is insignificant in this particular application.
    The relays are only consuming power while the vehicle is either running, or charging, or performing a deliberate deep discharge of the battery to remove voltage depression.
    During charging about 1.6kW are drawn from the grid to charge the battery, for several hours.
    During riding, the battery will only last for between 20min (full throttle 100km/h) and 2hrs (extremely gentle and slow driving). It uses up the 3.7kWh in the battery during this time. Typically it would be empty in about one hour of driving.
    If each of the 3 relays that are usually "ON" were using 0.5W (I think it is likely less), then a maximum of 1/2400th of the batteries energy would go into the relays during a typical drive. This results in a range reduction of about 24meters!

    I made a new simulation, it does not reflect 100% how the stock 12V system and the auxiliary SMPS 12V system interact, but it is close enough to show the principle. The relays which I think could be the above mentioned Opto-relays are marked SSR 1 to SSR8.

    Do you think this would work?

    [​IMG]

    The code for the simulator applet has to be posted in the next post, it got too long again!
     
  7. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    And here is the code to see in action in the applet simulation at http://www.falstad.com/circuit/
    (Relates to the immediate prior post):

    The battery segment voltages are set to 34V, 33.5V and 34V. At that level of imbalance none of the SSR1-4 are triggered. If you reduce the voltage of the middle battery segment to 33.4V it all starts to happen. Check what happens when the ON/OFF switch and the keyswitch are turned on and off, with and with out imbalance of >0.5V between any of the three battery segments.

    Code ( (Unknown Language)):
    1.  
    2. $ 1 5.0E-6 0.15814360605671443 48 5.0 50
    3. w 384 160 304 160 0
    4. t 240 112 304 112 0 1 -26.92352425166807 0.5929273226132352 50.0
    5. t 128 160 192 160 0 1 -0.18780107204514707 0.6331487532779221 50.0
    6. t 240 208 304 208 0 -1 33.272198589745315 -0.22802250270983393 50.0
    7. w 240 112 192 112 0
    8. w 192 144 192 112 0
    9. w 240 208 192 208 0
    10. w 192 208 192 176 0
    11. r 192 112 192 64 0 3300.0
    12. r 192 208 192 256 0 3300.0
    13. r 128 160 128 208 0 5900.0
    14. w 192 112 128 112 0
    15. w 192 208 128 208 0
    16. w 384 0 304 0 0
    17. w 192 64 192 0 0
    18. w 192 256 192 320 0
    19. w 192 320 304 320 0
    20. w 304 128 304 160 0
    21. w 304 192 304 160 0
    22. w 384 160 464 160 0
    23. w 464 160 576 160 0
    24. w 576 160 576 192 0
    25. t 512 288 464 288 0 1 -33.2728145437011 0.2274066209650485 50.0
    26. w 464 304 464 320 0
    27. w 384 320 464 320 0
    28. r 576 192 576 256 0 3300.0
    29. w 576 256 576 288 0
    30. w 512 288 576 288 0
    31. t 512 368 464 368 0 -1 26.765071538402285 -0.5935459889131991 50.0
    32. w 464 352 464 320 0
    33. r 464 384 464 432 0 3300.0
    34. t 608 336 576 336 0 1 -0.18780338906383776 0.6331492208144098 50.0
    35. w 576 288 576 320 0
    36. w 576 352 576 368 0
    37. w 576 368 512 368 0
    38. w 464 480 384 480 0
    39. w 576 480 576 464 0
    40. r 576 464 576 400 0 3300.0
    41. w 576 400 576 368 0
    42. w 576 256 640 256 0
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    47. w 384 0 464 0 0
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    50. r 352 352 352 416 0 3300.0
    51. w 576 160 656 160 0
    52. w 192 320 192 512 0
    53. w 192 512 608 512 0
    54. w 464 0 544 0 0
    55. x 915 237 991 243 0 24 Battery
    56. 174 96 144 128 176 0 1240.0 0.5 Resistance
    57. w 96 144 96 112 0
    58. w 96 112 128 112 0
    59. w 672 256 640 256 0
    60. 178 752 208 816 208 0 1 0.2 -0.0030456852722884537 0.05 1000000.0 0.0030 10.0
    61. 178 752 128 816 128 0 1 0.2 -0.0030456852722818145 0.25 1000000.0 0.0030 10.0
    62. w 608 512 752 288 0
    63. w 576 480 656 480 0
    64. v 880 352 880 320 0 0 40.0 34.0 0.0 0.0 0.5
    65. v 880 272 880 240 0 0 40.0 33.5 0.0 0.0 0.5
    66. v 880 192 880 160 0 0 40.0 34.0 0.0 0.0 0.5
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    73. 178 752 368 816 368 0 1 0.2 -0.0030456852722884507 0.05 1000000.0 0.0030 10.0
    74. 178 752 288 816 288 0 1 0.2 -0.0030456852722884503 0.05 1000000.0 0.0030 10.0
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    96. w 752 160 704 160 0
    97. 178 352 224 384 224 0 1 0.2 8.965145962491747E-10 0.25 1000000.0 0.0030 10.0
    98. 178 352 48 384 48 0 1 0.2 0.001957052172124008 0.25 1000000.0 0.0030 10.0
    99. 178 512 208 544 208 0 1 0.2 8.746986120296267E-10 0.25 1000000.0 0.0030 10.0
    100. 178 512 416 544 416 0 1 0.2 0.00200608688124587 0.25 1000000.0 0.0030 10.0
    101. w 192 0 288 0 0
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    111. w 352 352 352 320 0
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    124. w 640 304 640 336 0
    125. w 672 288 672 256 0
    126. 174 640 272 672 304 0 1240.0 0.5 Resistance
    127. 178 816 496 864 496 0 1 0.2 4.790419161676646E-5 0.25 1000000.0 0.02 500.0
    128. w 704 400 704 448 0
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    141. w 704 544 496 544 0
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    150. w 544 432 544 560 0
    151. w 416 560 544 560 0
    152. w 544 560 800 560 0
    153. w 800 560 800 544 0
    154. w 800 544 816 544 0
    155. w 48 544 48 224 0
    156. w 48 48 48 224 0
    157. x 806 521 832 523 0 8 Relay 1
    158. 178 1040 464 976 464 0 1 0.2 0.023999978043697263 0.05 1000000.0 0.02 500.0
    159. w 736 416 736 432 0
    160. w 736 432 784 432 0
    161. w 704 544 704 576 0
    162. s 816 496 816 432 0 0 false
    163. w 784 432 816 432 0
    164. w 864 432 816 432 0
    165. w 800 496 816 496 0
    166. w 800 496 800 528 0
    167. w 800 528 816 528 0
    168. w 864 512 864 528 0
    169. r 864 528 912 528 0 1000.0
    170. 162 912 528 912 576 1 2.1024259 1.0 0.0 0.0
    171. w 912 576 704 576 0
    172. w 1040 464 1040 432 0
    173. w 1040 432 912 432 0
    174. w 880 480 928 480 0
    175. w 928 480 944 480 0
    176. w 1040 528 1040 512 0
    177. w 944 480 976 480 0
    178. w 1040 464 1040 496 0
    179. w 1040 576 1040 528 0
    180. s 944 576 1008 576 0 0 false
    181. x 914 180 985 186 0 24 Vectrix
    182. x 924 293 975 299 0 24 IDeA
    183. x 916 344 1032 350 0 24 Segments
    184. x 808 558 834 560 0 8 NC/NO
    185. x 732 523 768 526 0 10 12V DC
    186. x 822 459 842 462 0 12 Key
    187. x 738 535 768 538 0 12 Stock
    188. w 864 432 912 432 0
    189. w 912 576 944 576 0
    190. w 1040 576 1008 576 0
    191. x 958 590 996 593 0 10 ON/OFF
    192. x 933 569 1023 572 0 12 Deep Discharge
    193. x 798 174 830 177 0 12 SSR8
    194. x 342 39 374 42 0 12 SSR1
    195. x 378 268 410 271 0 12 SSR2
    196. x 501 198 533 201 0 12 SSR3
    197. x 508 402 540 405 0 12 SSR4
    198. x 799 413 831 416 0 12 SSR5
    199. x 802 335 834 338 0 12 SSR6
    200. x 800 253 832 256 0 12 SSR7
    201. x 820 469 856 472 0 12 Switch
    202. w 768 496 800 496 0
    203. w 960 368 992 368 0
    204. o 63 64 0 35 40.0 0.1 0 -1
    205. o 62 64 0 35 40.0 0.1 1 -1
    206. o 61 64 0 35 40.0 0.1 2 -1
    207.  
     
    Last edited by a moderator: Oct 28, 2010
  8. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If you put an led across the cell leads, backwards, then the LED will light when the cell reverses.

    Use an opto to detect this.

    You can then get the signal from the cell or cells that have reversed via the opto completing the circuit.

    No relays needed.
     
  9. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Thanks for the suggestion, I don't think this would work. The cells initially only reverse to -0.25V, not enough to light an LED.

    Besides, attaching 102 LED's and 102 opto's to the battery sounds like pretty much the exact opposite of what I'm trying to do!

    I don't want to monitor individual cells, I just want to know when any cell is reversing, not which cell.
     
  10. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    I have improved the schematic so it now fits into the one simulation.

    [​IMG]


    The code below (for use with http://www.falstad.com/circuit/ ) has segment 2 of the traction battery set to 50.71V - just enough imbalance to trigger the warning LED when the other segments are at a super-full 152V each.

    Code ( (Unknown Language)):
    1.  
    2. $ 1 5.0E-6 0.27182818284590454 42 5.0 50
    3. t 128 96 192 96 0 1 -33.723390524028275 0.6033653583422023 50.0
    4. t 16 144 80 144 0 1 -0.5582865790365759 0.6188987897802036 50.0
    5. t 128 192 192 192 0 -1 45.02376829088657 -0.5738200104745772 50.0
    6. w 128 96 80 96 0
    7. w 80 128 80 96 0
    8. w 80 192 80 160 0
    9. r 80 96 80 48 0 6200.0
    10. r 80 224 80 272 0 6200.0
    11. r 16 144 16 192 0 255.0
    12. w 80 96 16 96 0
    13. w 80 192 16 192 0
    14. w 256 0 176 0 0
    15. w 192 112 192 144 0
    16. w 192 176 192 144 0
    17. t 384 240 336 240 0 1 -45.060609860833516 0.5736400916558253 50.0
    18. w 336 256 336 272 0
    19. r 464 144 464 208 0 6200.0
    20. t 384 304 336 304 0 -1 33.605355321683675 -0.6035472503406183 50.0
    21. r 336 320 336 368 0 5600.0
    22. t 448 272 416 272 0 1 -0.5582878564905513 0.6188994855058922 50.0
    23. r 480 400 480 336 0 6200.0
    24. r 512 336 512 272 0 255.0
    25. w 256 0 336 0 0
    26. r 352 64 352 128 0 6200.0
    27. r 240 272 240 336 0 6200.0
    28. x 821 207 897 213 0 24 Battery
    29. 178 624 128 688 128 0 1 0.2 -0.0029953769258922835 0.05 1000000.0 0.0030 10.0
    30. 178 624 48 688 48 0 1 0.2 -0.002995376925901064 0.25 1000000.0 0.0030 10.0
    31. v 752 272 752 240 0 0 40.0 51.0 0.0 0.0 0.5
    32. v 752 192 752 160 0 0 40.0 50.71 0.0 0.0 0.5
    33. v 752 112 752 80 0 0 40.0 51.0 0.0 0.0 0.5
    34. w 688 144 752 144 0
    35. w 752 128 752 112 0
    36. w 752 192 752 224 0
    37. w 688 224 752 224 0
    38. w 752 224 752 240 0
    39. 178 624 288 688 288 0 1 0.2 -0.002995376925892281 0.05 1000000.0 0.0030 10.0
    40. 178 624 208 688 208 0 1 0.2 -0.0029953769258922805 0.05 1000000.0 0.0030 10.0
    41. w 752 160 752 144 0
    42. w 752 128 752 144 0
    43. w 752 304 752 272 0
    44. w 752 304 688 304 0
    45. w 752 80 752 64 0
    46. w 752 64 688 64 0
    47. r 608 400 608 352 0 3900.0
    48. w 608 336 624 336 0
    49. w 624 320 608 320 0
    50. w 608 320 608 256 0
    51. w 608 256 624 256 0
    52. w 624 240 608 240 0
    53. w 608 240 608 176 0
    54. w 608 176 624 176 0
    55. w 624 160 608 160 0
    56. w 608 160 608 96 0
    57. w 608 96 624 96 0
    58. 178 240 208 272 208 0 1 0.2 9.113273295939559E-4 0.25 1000000.0 0.0030 10.0
    59. 178 240 32 272 32 0 1 0.2 0.00297118474243825 0.25 1000000.0 0.0030 10.0
    60. 178 384 160 416 160 0 1 0.2 9.047922759184787E-4 0.25 1000000.0 0.0030 10.0
    61. 178 384 336 416 336 0 1 0.2 0.002992880963330499 0.25 1000000.0 0.0030 10.0
    62. w 80 0 176 0 0
    63. r 192 80 240 80 0 5600.0
    64. w 240 64 240 48 0
    65. w 336 224 336 208 0
    66. r 336 208 384 208 0 5600.0
    67. 178 688 432 736 432 0 1 0.2 0.023604149461962105 0.25 1000000.0 0.02 500.0
    68. w 672 480 688 480 0
    69. w 0 32 0 208 0
    70. x 668 454 709 457 0 12 Relay 1
    71. 178 544 496 480 496 0 1 0.2 0.1527023648816179 0.05 1000000.0 0.02 1000.0
    72. w 608 336 608 352 0
    73. w 672 464 688 464 0
    74. w 736 448 736 464 0
    75. r 736 464 784 464 0 1000.0
    76. 162 784 464 784 512 1 2.1024259 1.0 0.0 0.0
    77. s 784 336 848 336 0 0 false
    78. x 820 171 906 177 0 24 Traction
    79. x 680 494 706 496 0 8 NC/NO
    80. x 393 531 450 535 0 16 12V DC
    81. x 938 479 1012 482 0 12 Key / Charger
    82. x 827 390 899 393 0 12 Stock 12VDC
    83. x 799 350 843 353 0 10 ON / OFF
    84. x 775 362 865 365 0 12 Deep Discharge
    85. x 670 94 702 97 0 12 SSR8
    86. x 266 77 298 80 0 12 SSR1
    87. x 270 253 302 256 0 12 SSR2
    88. x 415 207 447 210 0 12 SSR3
    89. x 409 381 441 384 0 12 SSR4
    90. x 671 333 703 336 0 12 SSR5
    91. x 674 255 706 258 0 12 SSR6
    92. x 672 173 704 176 0 12 SSR7
    93. x 956 400 1018 403 0 12 Relay 2 NO
    94. r 16 144 16 96 0 220.0
    95. r 512 272 512 224 0 220.0
    96. w 80 224 80 192 0
    97. x 773 102 813 105 0 10 34 cells
    98. x 769 262 809 265 0 10 34 cells
    99. x 769 184 809 187 0 10 34 cells
    100. w 240 48 80 48 0
    101. w 240 32 0 32 0
    102. w 80 0 80 48 0
    103. w 128 192 80 192 0
    104. w 240 256 240 272 0
    105. w 240 272 336 272 0
    106. w 336 272 336 288 0
    107. w 384 192 384 176 0
    108. w 384 176 352 176 0
    109. w 352 176 352 160 0
    110. w 272 48 288 48 0
    111. w 416 320 432 320 0
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    113. w 416 240 384 240 0
    114. w 416 288 416 304 0
    115. w 416 304 384 304 0
    116. w 432 320 448 320 0
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    118. w 432 464 304 464 0
    119. w 384 368 336 368 0
    120. w 240 336 240 384 0
    121. w 240 384 240 400 0
    122. w 240 400 384 400 0
    123. w 384 384 384 400 0
    124. w 384 400 480 400 0
    125. w 416 240 416 224 0
    126. w 416 224 464 224 0
    127. w 464 224 464 208 0
    128. w 464 144 464 128 0
    129. w 464 128 352 128 0
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    133. w 416 304 480 304 0
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    157. w 368 496 224 496 0
    158. r 192 208 192 240 0 5600.0
    159. w 240 240 192 240 0
    160. x 454 530 500 534 0 16 SMPS
    161. 178 1040 352 1072 352 0 1 0.2 0.021161957829434558 0.05 1000000.0 0.02 500.0
    162. w 384 336 368 336 0
    163. w 368 336 368 352 0
    164. w 416 176 432 176 0
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    183. r 64 528 112 528 0 1.5
    184. r 144 528 192 528 0 1.5
    185. s 224 528 272 528 0 0 false
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    188. w 544 480 592 480 0
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    190. w 0 496 160 496 0
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    197. w 608 400 608 448 0
    198. w 656 448 608 448 0
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    200. d 752 384 752 352 1 0.805904783
    201. w 752 416 752 384 0
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    204. v 912 400 912 368 0 0 40.0 12.0 0.0 0.0 0.5
    205. d 912 448 912 416 1 0.805904783
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    208. w 992 544 1072 544 0
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    213. s 944 448 992 448 0 0 false
    214. w 1024 560 1024 448 0
    215. w 912 448 944 448 0
    216. w 912 336 848 336 0
    217. x 759 86 819 89 0 12 Segment 3
    218. x 759 169 819 172 0 12 Segment 2
    219. x 759 249 819 252 0 12 Segment 1
    220. x 949 464 993 467 0 10 ON / OFF
    221. w 592 560 384 560 0
    222. w 384 560 336 560 0
    223. w 336 560 336 528 0
    224. w 336 528 304 528 0
    225. w 304 528 272 528 0
    226. w 192 528 224 528 0
    227. w 144 528 112 528 0
    228. w 64 528 0 528 0
    229. w 0 528 0 512 0
    230. w 0 512 0 496 0
    231. x 56 560 286 564 0 18 Cooling Impellers   ON / OFF
    232. x 801 484 895 488 0 16 Warning LED
    233. x 812 501 867 505 0 16 on dash
    234. x 374 545 500 548 0 10 (Relay represents isolation)
    235. x 525 540 579 543 0 10 90-156VDC
    236. x 821 137 879 143 0 24 NiMH
    237. x 432 35 520 44 0 40 IDeA
    238. x 385 50 565 53 0 12 (Imbalance Detection Apparatus)
    239. x 820 240 978 245 0 20 (102 cells x 30Ah)
    240. x 412 65 548 68 0 12 Vectrix version - untested
    241. x 13 331 194 335 0 14 SSR 1-8 = ASSR-1228-302E
    242. w 560 416 208 416 0
    243. w 208 416 208 272 0
    244. w 80 272 208 272 0
    245. w 208 272 240 272 0
    246. w 560 416 560 208 0
    247. x 10 400 175 404 0 14 12V SMPS: 4A continuous
    248. x 910 318 983 321 0 10 Tab 1 to SMPS
    249. x 12 356 163 360 0 14 PNP transistors: BF 470
    250. x 12 379 163 383 0 14 NPN transistors: BF 469
    251. w 496 144 576 144 0
    252. w 576 144 576 464 0
    253. w 496 464 576 464 0
    254. w 576 464 672 464 0
    255. w 608 48 576 48 0
    256. w 576 48 576 112 0
    257. w 576 112 400 112 0
    258. w 400 112 384 112 0
    259. w 384 64 352 64 0
    260. w 384 64 384 112 0
    261. x 712 299 743 302 0 10 Tab 1
    262. x 708 219 742 222 0 10 Tab 35
    263. x 708 140 742 143 0 10 Tab 69
    264. x 699 60 739 63 0 10 Tab 103
    265. x 909 301 994 304 0 10 Tab 103 to SMPS
    266. w 752 64 768 64 0
    267. w 992 336 1008 336 0
    268. w 1008 336 1008 384 0
    269. w 1008 384 1040 384 0
    270. w 1040 400 1024 400 0
    271. w 1024 400 1024 448 0
    272. w 1024 448 992 448 0
    273. w 1008 560 1024 560 0
    274. w 1072 544 1072 368 0
    275. w 1056 528 1088 528 0
    276. w 1088 528 1088 288 0
    277. w 976 304 1040 304 0
    278. w 1040 304 1040 352 0
    279. w 768 64 784 64 0
    280. w 784 64 1088 64 0
    281. w 1088 64 1088 288 0
    282. x 775 112 809 115 0 10 30-52V
    283. x 769 194 803 197 0 10 30-52V
    284. x 770 273 804 276 0 10 30-52V
    285.  
    286.  
     
    Last edited: Oct 30, 2010
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    Have you run any experiments on a battery cell to see how fast it will reverse under your expected current draw?
     
  12. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Sure have!

    In the first post of this thread you can see that it takes about 1min at 1.1A for one of these cells to go over the knee in the discharge curve.

    Under full throttle, >200A current draw it takes less than a second.

    The voltage of these cells bounces back up t about 1.2 V if the reversal was brief and they have some charge left.

    The higher the current draw, the faster the reversal.

    I'll try to dig up some of the graphs showing it more clearly.
     
  13. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Here is an overlay of graphs showing how empty 30Ah cells go over the discharge knee at 20A discharge current:

    [​IMG]


    They drop from about 1.17V to 1.1V within a few seconds. From there, it's almost vertically down to -0.250V (not shown).
     
  14. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Now to my questions on how to build this simulated circuit:

    1) What minimum voltage rating do I need to use for the transistors (for collector-base, collector-emitter and emitter-base voltage)?

    Each segment of the battery being measured has a maximum voltage of 51V. But the whole battery has a maximum of 153V.
    Do I need to use transistors rated for >51V or for >153V? This maximum voltage is not going to be reached very often, but during the occasional equalisation charge it could remain close to this voltage for several hours. Most of the time the segment voltages will be between 42V and 49V (126V to 147V total).

    How much safety margin is usually recommended for the transistor voltage ratings?
    Do transistors comfortably cope with running at their maximum voltage ratings or does it shorten their life?
     
  15. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    The simulated circuit continues to slowly mature.... nothing has been built as prototype yet.

    Below is the code for the latest version of the simulation. It is to be used in the applet at http://www.falstad.com/circuit/

    The simulated measurements which I have performed to evaluate the various permutations of this circuit are the following (among others). They all relate to the sensitivity (in mV) to imbalance at various battery SOCs ( = voltages).

    The questions to be answered were:

    What current flows through the opto-relays when there is no imbalance?
    What level of imbalance causes 0.8mA current through the opto-relays? (=> opto-relays should be opening again when current falls below 0.8mA);
    What level of imbalance causes 3mA current to the opto-relays (=> closing and triggering the "imbalance detected" response)

    Following are the answers to these questions for a number of different SOC's (for a 102s NiMH battery):

    At 154V ( = 51.33V/segment 25.67Vx2/segment 1.51V/cell ): (Battery voltage does not normally get that high - it is just to test with a safety margin)
    without imbalance: 46microA to opto-relays; just <800microA @ 180mV ; 3mA @ 370-390mV imbalance.

    At 151V ( = 50.33V/segment 25.17Vx2/segment 1.48V/cell) :
    without imbalance: 44microA to opto-relays; just <800microA @ 180mV ; 3mA @ 370mV imbalance.

    At 145V ( = 48.33V/segment 24.17Vx2/segment 1.42V/cell): (This is about the final charge voltage for n EQ "Freddy" charge at 0.3A @ 32degC)
    without imbalance: 41microA to opto-relays; just <800microA @ 190mV ; 3mA @ 370-390mV imbalance.

    At 140V (46.67V/segment 23.33Vx2/segment 1.37V/cell) : (Voltage settles about here after a normal charge)
    without imbalance: 38microA to opto-relays; just <800microA @ 190mV ; 3mA @ 380mV imbalance.

    At 125V (41.67V/segment 20.83Vx2/segment 1.23V/cell) :
    without imbalance: 32microA to opto-relays; just <800microA @ 190mV ; 3mA @ 390mV imbalance.

    At 91.8V (30.6V/segment 15.3Vx2/segment 0.9V/cell) : (Most of the time it will not get that low)
    without imbalance: 16-19microA to opto-relays; 745mA at 230mV imbalance ; 3mA at 400mV - 420mV imbalance.


    Segment currents at 154V (mA): (causing imbalance if unequal)
    Segment 1 : 175.27mA
    Segment 2 : 175.24mA
    Segment 3 : 175.27mA

    Max power at balancing resistors at 154V : 263mW

    Hope it makes some sense to you!

    I would very much appreciate if someone could check if the chosen components are suitable for the voltages they will experience in the circuit!
    Data sheets here:
    http://www.nxp.com/documents/data_sheet/BC846_BC546_SER.pdf
    http://www.nxp.com/documents/data_sheet/BC856_BC857_BC858.pdf
    http://www.farnell.com/datasheets/358205.pdf

    The code needs to follow in the next post due to the 10000 character limit.

    Don't worry if you don't now if NiMH batteries can be managed that way or not - I am after advice on how to choose the appropriate components for this circuit. Real world tests can then show if (or if not) it is suitable!
     
  16. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Here is the code relating to the previous post: ( for the applet at http://www.falstad.com/circuit/ which can also be installed on you computer).


    Code ( (Unknown Language)):
    1.  
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    192. x 784 494 878 498 0 16 Warning LED
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    195. x 525 540 579 543 0 10 90-156VDC
    196. x 432 35 520 44 0 40 IDeA
    197. x 385 50 565 53 0 12 (Imbalance Detection Apparatus)
    198. x 412 65 548 68 0 12 Vectrix version - untested
    199. x 13 331 194 335 0 14 SSR 1-8 = ASSR-1228-302E
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    350.  
     
    Last edited: Nov 8, 2010
  17. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I'd select transistors rated for at least 20% more voltage than the max expected, and de-rate their current capacity at least 50% from specifications.

    For example, a 2N3904 is rated for Vceo=40v, Ic=200mA. However, if you use it with Vceo>32v or Ic>100mA, your chances of it working for any length of time go down considerably.

    Don't forget about power dissipation issues.

    Be conservative.
     
    Mr. Mik likes this.
  18. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Thanks for that explanation!

    It seems like the components can just sneak in within the limits you suggest!

    The three battery segments should in normal operation never be above 154V/3= 51.33V. Unless I have missed some possible failure mode, this is the maximum emitter-collector voltage that the transistors can be exposed to.

    51.33V x 120% = 61.6V; The data sheet specifies a Vceo of 65V - there is the first tick!

    The maximum current Ic from the transistors through the opto-isolators is about 9mA - that's only 10% of the 100mA rating in the data sheet - another tick!

    Ahem, yes, I would have forgotten that, thank you!

    I guess the problem lies here: The transistors can take 65Vceo; or they can take 100mA Ic; but they cannot take 65V at 100mA = 6.5W. Nowhere near that much! The rating is between 150mA and 250mW, depending on the form factor:
    SOT23 - 250 mW
    SOT323 - 200 mW
    SOT416 - 150 mW
    SOT54 - 500 mW
    [​IMG]
    With the components shown in the last circuit simulation it looks like the power dissipation always remains under the 150mW maximum limit per transistor, but I'd like to reduce it even more, if possible. I hope this would keep the transistor temperature more stable, that's important because the hFE increases with increasing temperature.

    But, is this actually the correct way to calculate the power dissipation of a transistor? By multiplying Vceo with the Ic current that is present at the same time?

    For example I calculate the power dissipation as 25.87V x 4.54mA = 117mW (the peak value I could find) - is that the way to calculate it?
    [​IMG][​IMG]
     
  19. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You tried to host files from your computer to the Internet. That doesn't work; you must first upload them to AAC using the "Go Advanced" and "Manage Attachments" buttons.

    Power dissipation issues:
    You need to look at power dissipation when the transistor is saturated. In many datasheets, typical saturation curves are shown where Ib=Ic/10. Basically, you want to stick with that formula; whatever you expect to see as the collector current, provide 1/10 of that for the base current. If you fail to provide enough base current, the transistor will drop out of saturation, and power dissipation in the transistor will increase dramatically.

    Enhanced-mode power MOSFETs are vaguely similar to transistors, but they are controlled by voltage instead of current. Instead of a "base", they have a "gate"; instead of an "emitter" they have a "source", instead of a "collector" they have a "drain".

    Very basically, the "gate" is the "valve" that controls current flow between the drain and source terminals. When Vgs (voltage on the gate referenced to the source terminal) is equal to zero, the MOSFET is "off"; there is nearly infinite resistance between the source and drain terminals.

    For standard MOSFETs, when Vgs=10v (-10v for P-channel) the MOSFET is considered to be turned fully ON, and the resistance between drain and source terminals is specified as Rds(ON). There are also logic-level enhanced MOSFETs; you will recognize them by looking in the datasheets and seeing Rds(ON) specified with a Vgs of 4.5v or 5v.

    MOSFETs have a "gate charge", which is normally specified in nC's (nano Coulombs). Basically, they act more or less like capacitors; you have to charge and discharge the gates.
     
  20. Mr. Mik

    Thread Starter New Member

    Oct 26, 2010
    23
    0
    Thanks for your detailed reply.
    I guess it's time for me to read up on the basics about semiconductors and transistors....then I shall understand this.
    Thank you so much for this explanation!

    Yesterday I was almost ready to throw in the towel on this approach to the "IDeA" circuit. Now I think that the Opto-Mosfets may be particularly suitable for the job, with some added resistors to control at what current they turn on.

    Here is what I wrote on another forum about it, before I re-read your above explanations and then understood that the results of my little experiment were exactly what you were trying to explain to me!


    Well, now I'll look into this with new vigour, because it seems to me that the "capacitance of a Mosfet gate" should make it possible to control for differences between individual devices by adding closely matched resistors across their input. If the Mosfets for some reason have different capacitances, then it will take different lengths of time for them to turn on, but they will eventually turn on at practically identical currents supplied by the transistors in the IDeA circuit! It does not matter in this application if it takes 50us or 2s - as long as they turn on within a couple of seconds!

    Here is a schematic showing the circuit with all that resistance - but the LED still lights up! The resistor labelled "R adjust" changes this: With a 330ohm resistor the opto-mosfet switches on when there are about 3mA flowing.
    [​IMG]

    Now I have another question: How on earth does an Opto-Mosfet manage to achieve optical isolation when only using 1uA on the supply side? I don't think that is enough to create a detectable amount of photons to cross that "optical isolation" barrier line in the schematic? Or what am I misunderstanding this time?
    http://www.farnell.com/datasheets/358205.pdf
     
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