Tesla 5.3 kWh Battery Module Monitoring Board - Part 1

The recent availability of salvaged Tesla battery packs has led to efforts to repurpose them for solar applications (see reference at end below) and it might be possible to use them in this BMW 325i EV conversion project as well.   The primary concerns with using salvaged Lithium ion batteries include the condition of the batteries when received, and the additional requirement of safe handling when later charging and discharging the batteries after installation.  For safety, either the purchase or the development of a battery monitoring system capable of controlling 6 or more of the Tesla modules, each containing essentially 6 batteries (36 total) is a must.  For purpose of better understanding and possible reverse engineering of the Tesla battery control board, a monitoring board was purchased from K-Ash on Ebay.  (Picture DSC05118)



Picture DSC05118 of the component side of the Tesla battery control board.  There is one of these boards located on each battery module.

The board as received was copyright 2012, and it is labeled PCAB (1020796).  It has a white sticker labeled 1021749-00-REV 03 and 0314C60002094.  The board is designed to monitor the 6 cell groups contained in each module. 

The black 16 pin chip (U4) on the upper left of the board is an SI8642 and it is an isolator chip to separate high voltage from ground.  http://www.silabs.com/Support%20Documents/TechnicalDocs/Si864x.pdf

The black 64 pin chip (U1) in the lower center (largest chip) of the board is a Texas Instruments TI BQ76PL536A battery monitoring chip.  http://www.ti.com/lit/ds/symlink/bq76pl536a-q1.pdf

The C8051F536 microprocessor (U100) that controls the board is immediately to the left (and slightly higher) than the 64 pin battery monitor chip (U1).   http://www.silabs.com/Support%20Documents/TechnicalDocs/c8051f52x-f53x.pdf 

                     

 Picture DSC05126 showing the  three connectors used on the reversed side of the Tesla battery control board.

The long 15 pin white connector (J3) is a JST S15B-PASK-2 (the mate to this connector is JST PAP-15V-S and it uses SPHD-001T-P0.5 crimp pins).  It is labeled as Cell 6, 4, 2, 0, 1, 3, 5, with every other pin left unconnected for further voltage isolation.   The cable that attaches to this connector is terminated at six different locations on the battery pack.  

The large black 10 pin connector (J1) is a Molex Mini-Fit Jr Series 5569 and it is available from DigiKey ( http://www.digikey.com/product-detail/en/molex-llc/0015978102/0015978102-ND/3157084 ). 

The corresponding mate to J1 can be purchased here:  http://www.digikey.com/product-detail/en/molex-connector-corporation/15-97-5101/WM4772-ND/1624637

The small white connector (J6) is a JST S4B-PASK-2 and the mate is JST PAP-4V-S.  The pins are labeled TS1+, TS2+, TS2-, TS1-.  These are the thermistor leads (Temperature Sensor).

The Tesla PC board is fastened to the module housing with four black attachment pins.

Picture DSC05236 showing one of the mounting points with the inserted attachment pins.  Using a pair of needle nose pliers the small center pin can be pulled out (DSC05237).

Picture DSC05237, once the pins are fully removed, the remaining black piece pulls smoothly away from the battery module's plastic frame.  




Picture DSC05127 showing the dimensions of the Tesla battery control board.  These dimensions can be used to fabricate a proto board that can be directly attached to the existing 5.3 kWh Tesla battery module. 
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UPDATED 12-31-2016
Error: the 102.5 noted as the horizontal distance between the left and right mounting points in the picture above is actually 92.5 mm.

Picture DSC05357 showing that the BMS side of the board actually has a total of six mounting points that may be used when fabricating a replacement printed circuit board.  The left four were described above, but the right two were discovered upon further examination.  The top row of three mounting points are all 49 mm above the bottom row of three mounting points.  The distance between the far left pair and the center holes is 92.5 mm, and the distance between the center pair and the far right pair is 79 mm.
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Examples of Tesla Modules being used in a Solar Project

An example of a solar project is http/wk057  where an off grid battery system was constructed that used 36 batteries (191.25 kWh) from 2.25 salvaged 85 kWh Tesla cars. ( https://teslamotorsclub.com/tmc/threads/plan-off-grid-solar-with-a-model-s-battery-pack-at-the-heart.34531/ ).  The project also includes an attempt to produce a custom BMS controller as a plug in replacement for the Tesla battery control board.  Some pictures of that project can be found here:   
(  https://teslamotorsclub.com/tmc/threads/in-development-inexpensive-custom-bms-for-tesla-battery-modules.51095/  )


Par 2 of this blog was posted on 2/5/2018?

Tesla 5.3 kWh Battery Modules Overview

Six Tesla Model S battery modules, rated 24V, 250Ah, 5.3kWh, and comprised of 444 Panasonic 18650 3400mAh cells, configured 6S74P, were purchased from A-Kash on Ebay.  These batteries will provide the same 144 volt nominal pack voltage as the Yellow tops currently being used, but since they can be discharged more completely, better range will be achieved.  These batteries will initially be monitored using an Orion controller and conveniently, the Orion is directly compatible with the Eltek 67.115.0 charger already being used and described in this blog's May 15, 2016 posting.

Comparison of 6 Tesla Batteries Versus 12 Yellow Top Batteries

The total pack voltage is approximately the same at 144 volts.
Weight of the 6 Tesla batteries is about 330 pounds compared to 717.6 pounds for the 12 Yellow Top 8050-160-FFP-D31T batteries.
The 6 Tesla batteries should provide 31.8 kWh and it is anticipated that about 80% of the contained energy will be available for use.  The 12 Yellow Tops provide about 10.8 kWh of which about 50% of the contained energy is expected to be available.  It is estimated that this 1992 325i EV conversion requires about 400 watt-h for each mile travelled, then the Tesla batteries should allow for a range of about 63.6 miles compared to the Yellow Tops expected range of 13.5 miles.

Upon arrival the modules measured between 23.09 and 23.12 volts. These batteries were extracted from a 2015 Tesla Model S (vin 5YJSA4H29FFP74017)  which originally used a 85 kWh pack.  The VIN can be decoded here: https://teslamotorsclub.com/tmc/threads/decoding-tesla-model-s-vins.7638/

Each battery module is labeled with a sticker that indicates both a part number and a serial number.  All of the batteries received were part number (P) TPN 1009312-00-E.  The following serial numbers and corresponding module voltages were recorded:

Tesla Batteries Ability to Hold Charge

                                         12/7/2016           1/29/18                              1/26/19                             5/25/20
(S) TSN T14G824536     23.09 volts          23.07 volts    (-0.09%)       23.03 volts   (-0.17%)    22.86 volts   (-0.74%)
(S) TSN T14G824283     23.11 volts          22.29 volts * (-3.55%)       21.74 volts * (-2.47%)   21.60 volts*  (-0.64%
(S) TSN T14G824610     23.11 volts          23.10 volts    (-0.04%)       23.07 volts    (-0.13%)   23.07 volts    (0.00%)
(S) TSN T14G824617     23.12 volts          23.08 volts    (-0.17%)       23.03 volts    (-.022%)   22.81 volts    (-0.96%)
(S) TSN T14G824692     23.12 volts          23.09 volts    (-0.13%)       23.06 volts    (-0.13%)   23.05 volts    (-0.04%)
(S) TSN T14G824708     23.12 volts          22.30 volts *  (-3.55%)      21.76 volts *  (-2.42%)  21.72 volts*  (-0.18%)
Updated 1/29/18;  1/26/19;  5/25/20 
                                  6/14/2021    compared to voltage on 12/7/2016
(S) TSN T14G824536     22.7 volts    (-0.39 volts, or -1.69% from 12/7/2016)
(S) TSN T14G824283     15.6 volts *  ouch
(S) TSN T14G824610     22.8 volt      (-0.31 volts, or -1.34% since 12/7/2016)
(S) TSN T14G824617     22.5 volts     (-0.62 volts, or -2.68% since 12/7/2016)
(S) TSN T14G824692     22.8 volts     (-0.32 volts, or -1.38% since 12/7/2016)

(S) TSN T14G824708     21.5 volts *        

Updated 6/14/21 

Note that over the period of 12/7/16 to 5/25/20 (1265 days) the average loss in voltage for the six batteries amounted -2.567% per battery over a 1265 day (3.518 years) period.  This is a loss of about 0.73% of the original voltage level per year.

Updated  5/25/20, 6/14/21 

If we ignore the two batteries that were damaged, the average voltage of the remaining 4 batteries is 22.7 volts.  The average voltage of the same four batteries on 12/7/2016 was 23.11 volts.  This represents an average change of -0.41 volts (-1.77%) over a 1650 day period (4.521 years).  
Updated 6/14/21 

  
*  These two batteries were installed in the battery box and briefly shorted with a socket wrench (blog entry 6/18/17, picture DSC05985).  The other four batteries have never had a load placed on them.  Note that the voltages suggest essentially no leakage during 13 months of storage.

This will probably be the end of the long term stability test for the batteries and the installation of the Orion BMS will now begin.

Updated 5/25/2020

Picture DSC05178.  After removing the orange rubber terminal protectors on the left, this module (serial # 4610) was found to be partially charged and 23.11 volts. The terminal landing areas (Picture DSC05298  ) under the orange plugs are 37 mm x 37 mm with a M8 x 27 mm center bolt.

Picture DSC05298 of the low voltage terminal (left side when viewed from the top) after removal of the orange cover.

Updated 5/13/18

Picture DSC05176.  Each battery module has a BMS control PC board located at one end.  The yellow tape (one at the left and two at right)  secure the top and bottom plastic vacuform type covers to the module.  The tape appears to be a Polyamideimide tape (likely Kapton, see https://www.uline.com/BL_6407/Kapton-Tape?pricode=WE491&AdKeyword=kapton%20tape&AdMatchtype=e&gclid=CPWO2_v4y9ACFZA2aQod4YMFgQ&gclsrc=aw.ds  )

Picture DSC05191 After removal of the four black mounting pins the control board can be pulled away from the module to reveal a pair of white connectors.  The white left 15 pin connector is used to measure the voltage of six battery subgroups of cells.  The right connector  with pairs of blue and yellow wires are connected to temperature probes.  The white connectors can each be removed by first pressing the top center tab (corrected 4/28/17) and gently prying upward while pulling on the connector.  The Gold surfaces at the top of the picture are the tape covered bent ends of the module's heating/cooling coils.

Picture DSC05196  showing the four wires that travel on the top of the pack (black, red, yellow, and blue) and the three wires on the bottom of the module (green, blown and orange).  Each of the wires is connected to a different region of the battery surface (Picture DSC05186) and provide different voltage measurements (see below).

Picture DSC05186 showing one of the wires that is welded to a region of the metal face plate.

Picture DSC05192 showing a close up of the right side temperature sensor (TS) which is connected to the BMS board with a pair of blue wires.  The left side (yellow wires) temperature sensor measured 13.74 k ohms and the blue sensor wires measured 13.79 k ohms.

Picture DSC05195 showing the measurement wires that are terminated (welded, picture DSC05186 above) to different regions on the face of the battery module.  The silver surfaces appear to be contiguous, but actually they are cut to provide four separate regions on one side of the battery and three separate regions on the reverse side.

A Klein Tools CL2000 digital Voltmeter was used for all measurements.  The CL2000 can measure up to 1000 volts DC and up to 400 amps DC.   The following voltages were measured from Left Terminal (when viewed from the top with the bms board close to the viewer ) of a battery (serial # 4610) to each of the sensor wires:

Cell 6 - blue    -   23.10  volts
Cell 4 - yellow -   15.40  volts
Cell 2 - red      -     7.70   volts
Cell 0 - black   -     0.00   volts
Cell 1 - brown -     3.86   volts
Cell 3 - orange -   11.55   volts
Cell 5 - green   -    19.26   volts

Voltage between Left Terminal  (-) to Right Terminal  (+) = 23.1 volts

Updated 1/29/18
Updated 5/13/18

The pack is considered to be 0% State of Charge (SOC) when the module measures 18.6 volts.  A 70% charge typically measures 23.1 volts, and a 100% charge is about 24.9 volts.

DSC05180 showing the side of the module opposite to the electrical control side.  Each coolant line was shipped sealed with black caps to prevent residual coolant from leaking out during shipment. The three gold regions are the Kapton covered u-bends of the serpentine cooling tubes that make 8 lengthwise passes through the battery pack.  Note that the vertical positions of the nipples are different.  The left side (input) is lower than the right side (output).  

Picture DSC05232 showing a close up of  the 5/16" coolant nipple after the black cap was removed.   

The cooling loop uses a pair of 5/16" (ID) tubing nipples that appeared to a Dorman 800-080 or 800-120 type Fuel Line Quick Connector.  Although these connectors were tested both bottomed out when installed and neither snapped tight as anticipated.  Although one can probably install straight tubing with hose clamps, we are still looking to source the correct couplings.
Details of Dorman connectors can be found here:  http://www.dormanproducts.com/gsearch.aspx?type=keyword&origin=keyword&q=fuel+line+connector  .  These connectors can also be purchased (Dorman, ebay.com and Amazon.com) and they are available for different tubing sizes, as straight, 45 degree and 90 degree angled fittings.

------------------
UPDATED 12-19-2016

It was found that Dorman 800-116 Fuel Line Connectors (Summit Racing, part RNB-800-116, at $7.97 per pair) appear to work very well.  These fittings are described as 5/16" Steel to 5/16" (8 mm) Nylon Straight and the connectors  snap on tightly yet can still be removed easily by pressing the tab located on the side.

Picture DSC05324 of the Dorman 800-116 connector after one was snapped onto the Tesla battery cooling fitting.  Some pale blue coolant fluid spilled out during the effort.

Picture DSC05325 close up of both sides of the fitting.  Release tab is evident on left side of the bottom fitting.

Picture DSC05327 of the blue colored fluid that was recovered from the module.   In one of Tesla's battery patents ( http://www.google.com/patents/US20140178722  ) this fluid is described only as " water or another coolant, such as any conventional anti-freeze mixed with water, oil, or even cold air ".   The blue color suggests that the fluid is Propylene glycol, but time permitting, this fluid will later be tested for both concentration and identity.

---------------------

Picture DSC05287:  Each Tesla battery module has a "fin" on each side which extends the majority of the length of the module.  When looking at the modules from the battery terminal end, the right side "fin" has a maximum width of 0.5" (top unit, the rounded section with 7/32" holes) and the remainder of the "fin" is 5/16".  The left side "fin" has a width of  0.375" (bottom unit).  These fins will be used to support the modules in a Mounting Frame that is being constructed that will support 4 batteries.  The Mounting Frame will then be isolated within a Stainless Steel battery box, and the battery box finally placed within the trunk located wheel well of the 325i.   

Picture DSC05230  showing close up of the rear portion of the left hand rail (or "fin") that is 0.375" wide and 0.125" thick.   

Battery Charger for the 144 volt Pack of Optima Yellow Top Deep Discharge Batteries

The 12 individual Yellow Top batteries have until now been individually charged using a Sears battery charger.  This process, although adequate for testing, is not conducive to using the car as a daily ride.  Consequently, different battery chargers were investigated to see which one might work for this project.  The design criteria included that the batteries and the charger must at all times be isolated from the chassis and it must be able to provide about 171.6 DC volts.  For the initial charger tests an Eltek 67.115.0 was selected (Picture DSC04736) from evolve electric  ( http://evolveelectrics.com/ ).  The charger ($1261.48 including shipping) can also be purchased with a liquid cooling chill plate ($314 extra).  Since the charger will be located in the trunk and for the moment there are no cooling lines available, the charger was modified in David's shop with the addition of an Aluminum heat sink and twin 12 volt fans (Pictures DSC04743 and DSC04731).

Picture DSC04736 showing the original Eltek 67.115.0 charger (6.29 kg after adding wiring connections on the left side).

Picture DSC04737 showing the name plate specifications of the Eltek 67.115.0 charger.

Picture DSC04743 showing the charger (on the left) after the addition of a 6.5" x 14" x 1.375" Aluminum heat sink.  The control cover (right side) has twin fans, a control box with output display, and a computer port for connection to laptop and programming.

Picture DSC04731 showing the end on view with the heat sink and control cover in place.  The air is pulled through the heat sink and exhausted away from the unit.  The complete charging system was 7.3 kg.

Operation of the Eltek 67.115.0 Charger

The Eltek 67.115.0 charger is a 3 KW charger and it is controlled via the CAN bus.  It can provide between 78 and 180 volts DC and a maximum of  23 amps.  The Eltek technical manual can be found here:  http://evolveelectrics.com/PDF/Eltek/Eltek%20Guide%20IP67.pdf   

Upon application of power, the charger begins continuously transmitting an identifier statement as it waits for instructions.  An 18F Series PIC microcontroller with CAN interface was selected by David due to his previous experience with the device.  The PIC under software control provides messages on the CAN bus that include current limit, voltage limit, power limit, and enable command.  The PIC sends the charger these commands several times each second, and if the Eltek charger does not receive a command within 1000 milliseconds. then the charger outputs an error condition, shuts down, and reverts to sending only its  identifier statement.  When the charger receives the control command, it then responds by sending (about 5 times per second) 3 different messages.  Status 1 (a lot of data which also includes voltage and current), Status 2 (more data which also includes power and temperature), and Errors.  The PIC uses these status messages to provide information to the display and to collect data that it can provide to an external data logger program.

Manufacturer Recommended Charging Cycles

The requirements for charging Yellow Top batteries (and many others) can be found at http://batteryuniversity.com/  or by review of some Xantrex charger's technical data sheets.  Each type of battery has a manufacturer's recommended charging cycle which must be followed to avoid causing damage to the cells, and the requirements for Lead acid batteries are very different from Lithium batteries.   In the case of the 12 volt Yellow Top batteries, each battery is initially charged at 14.3 volts followed by a trickle charge at 13.4 volts.

Algorithm for the charge cycle

The software was written by Chris in about 20 hours and is about 500 lines of C code.  With all the drivers and libraries the program is about 1300 lines.

The start of the charging cycle is called the Stage 1 Bulk Charging Mode in which the charger is amperage limited.   The Eltek 67.115.0 can provide 23 amps, but we elected to limit it to 20 amps.  The battery voltage gradually rises at the fixed amperage, and the Bulk Charging is continued until the voltage reaches 14.3 volts per battery, or 14.3 x 12 (batteries) = 171.6 volts for the pack.  After reaching the maximum voltage, Stage 2 (Absorption) charging begins where the voltage provided by the charger remains constant (at 171.6 volts), but the amperage drawn by the batteries gradually decreases.  Stage 2 ends when either the amperage falls to 2% of battery capacity ( Yellow Tops are 75 amp hour, thus 0.02 x 75 amp hours = 1.5 amps) or, a total of 3 hours has passed while in Stage 2 (this is a safety limit we elected).  Upon completion of Stage 2, Stage 3, or the Float Charge Stage, begins.  In the Float Charge Stage the Eltek voltage output is reduced to the manufacturer's recommended 13.4 volts per battery (or 13.4 x 12 = 160.8 volts for the pack).

Picture showing the bench testing of the display.  The 12 volts required to operate the PIC microcontroller and the display was derived from the J-1772 plug.  Two fuses were added within the charger, and then the power was supplied to a 12 volt power supply located within the control box. (Picture DSC01604).

DSC01604 showing the computer interface (black far left), reverse side of the display board (green), and the 12 volt power supply located within the control box.  (updated 9/7/2017)

Picture of the resistor banks that David used for the initial testing of the charger.

The next step will be to establish the wiring diagrams that will connect the J-1772 charging port (on the side of the car), the Eltek 67.115.0 charger, the batteries, and a J-1772 AVC2 board (to provide handshaking to public charging stations).   Finding a good location within the trunk and the fabrication of mounting brackets will then finalize the effort.