ElectroClassic EV
Classic Cars Reborn into the Electric Future

Battery Management Rethunk

enroute_pasadenaWith the batteries less than fully charged, my lovely wife and I headed toward Pasadena to visit friends. Even though the pack was not full, it had spent the entire previous night soaking up electrons, so I wasn’t particularly worried. The drive is only about 25 percent of my projected range, and the needle on my anxiety meter was snoozing. So when the low voltage alarm sounded just a couple miles from our destination, I suspected a loose signal loop wire or some such, and continued driving. That was until my ultra-cool EV came to an ultra-uncool dead stop just a quarter mile from the finish line. We grabbed our bags from the trunk and walked the rest of the way to my friend Michael’s house, who threw a box of straps in his Prius and towed the electric Porsche the last leg.

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michael_mb_1Once in the driveway, Michael set me up with an outdoor 110 volt outlet. I plugged-in and cycled the ignition switch to reset the MiniBMS control board. Unfortunately, the charger remained disabled and the alarm continued to sound. I popped the motor bay hatch to peek at the rear packs, and noticed that cell #9 BMS module was dark, causing me to think the module had gone bad. I removed the yellow signal path wires from #9 terminals and tied them together, bypassing the suspect module. The alarm stopped, so I cycled the ignition again to reset the BMS, and the charger began a new session. Voila. (Thanks to Penny for capturing this moment.)

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night_drive_tunnelBy the following afternoon, the charger had completed its final cycle and the pack was full. Furthermore, cell #9 module was glowing green again. I didn’t know if it would cause another event on the drive home, so I left the bypass in place. My little 914 took the old Arroyo Parkway like a bullet – swift, steady, and delivering us home in much less time than usual.

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bms_modules_ecuThe next day, an email exchange with CleanPowerAuto revealed that the cell module had behaved as designed. The module went dark to indicate that lithium iron phosphate cell #9 had edged into deep discharge. The restored green LED signaled the cell’s return from dangerous territory. Given these new revelations, here are my conclusions:

1 – Cell #9 was always undercharged, and probably never went into shunt mode during initial pack balancing.

2 – The entire pack was at a low charge state because the charger reached a heat threshold and throttled back.

3 – Since I had not yet installed a state-of-charge meter, I did not realize the entire pack was low.

4 – I need a more sophisticated BMS that will provide detailed battery data on a cell-by-cell basis.

5 – I want a BMS that will wirelessly transmit that data to a touch screen installed in the cockpit.

6 – I need a BMS that will perform a more controlled and exact balance on the entire pack on a cellular level.

7 – The true health of cell #9 will not be known until the new BMS is installed.

8 – If the new BMS reflects any possible injury to cell #9, the cell will need to be replaced.

9 – Unless I exclusively use more efficient 240 volt Level 2 charging, I will need to install better charger ventilation.

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The MiniBMS performed exactly as advertised, living up to its name by taking up minimal space. But I wanted more control over each cell, including monitoring, reporting, real-time display, automated pack balancing and CAN integration, so the MiniBMS came out. Above is the box-load of modules that were removed from each cell in the pack. I will bundle these with the small control board, the current sensor and state-of-charge meter, and probably turn the whole system around on Electric Car Forum or DIY Electric Car forums. It’s a good distributed BMS at a decent price, and should make somebody very happy who is looking for an economical BMS solution. By the way, here is a nifty little video that explains why the main pack load should be disconnected before working on any BMS.

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Shown above is the Orion Battery Management System, built by Ewert Energy. It was given high marks by HPEVS, the maker of my AC-50 drive motor – who is in the process of integrating it with the Curtis controller. With that endorsement, I ordered one for myself. I’m impressed that it performs a very controlled top-balance on the pack by selectively draining cells that reach capacity before the rest, giving all cells equal opportunity to rise to the fullest charge. It literally levels the playing field. It also monitors the health of the pack by collecting real-time data about the condition and performance of each cell. It creates logs of all the data streams for later inspection, and is programmable to allow software tweaking of key parameters. Finally, it allows a way to send that real-time data via Bluetooth to a touchscreen display that will look bitchin’ in my center console.

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After meditating on placement, I decided the best home for the Orion was under the passenger side dashboard. Because the Orion is a centralized BMS, it consolidates all monitoring and control into a single unit too large for the prior location. It also prefers to be away from moisture and the elements, eliminating the rear motor bay as a mounting location. Shown above is the fabricated mounting plate taped under the dash for test positioning. Located here, the Orion will be accessible yet out-of-the-way, and will be near most of the electrical connections it requires at the front of the car.

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After poring over the manual, I segregated the wires according to their connections; either inside the cockpit, or beyond the firewall. The bundle in black heat shrink traveling off to the right is the pack voltage sensor and main I/O leads that will access various power sources in the former fuel bay. The loop of white/orange wires at lower left provide a way to drive existing analog gauges using 0-5 volts. The yellow/brown loops at the top left are for cooling fan power and control. The two black loops are the CAN bus (Control Area Network) connections, and the white loop wires are undesignated in the manual.

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Each cell in the pack needs to have a tap lead that delivers real-time data back to the Orion BMS main unit. Shown above are three bundles of 12 cell taps that will connect directly to the battery terminals. The red bundle will pass through the dash firewall into the ex-fuel bay, and the two orange bundles will travel to the rear pack through the ex-heater duct on the passenger side. I used a cable snake to pull them down through the duct inside the rocker panel, emerging in the motor bay under the battery packs.

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After entering the engine compartment, the cell taps were separated into two groups, bundled with heat shrink tubing, and directed to the tops of the rear battery packs. Each bundle has one ground lead, one temperature sensor wire pair for the thermistor, and a tap lead for all of the 12 cells in the packs.

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Here is the Orion securely mounted under the passenger side dash. Half of the main I/O harness is threaded through the bulkhead into the ex-fuel bay, and the remaining dangling wires will be either routed or tied-off. The three cell tap ports visible on the right side of the Orion provide management for up to 108 cells on this unit, though I will only use 36.

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orion_rear_packsHere are the cell tap wires routed and dressed-out for both rear packs. Notice the taps run to the positive terminal of each cell, in the same serial order as the cells in the pack. The MiniBMS didn’t care about numerical cell order, but the Orion tracks cells individually, so I renumbered them in serial order for better indexing. The thermistors are tucked down between the ribbed sides of the center cells of both packs to a depth of about 4 inches. The right pack thermistor wires can be seen ducking down between cells #33 and #30 above.

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front_pack_tapsHere’s the finished front pack with dressed-out cell tap wiring. It looks pretty straightforward, but both the above two images involved some main cable rerouting and represents about 8 hours of very tedious work.

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control_box_reduxNext comes an overhaul of the control box in the front fuel bay area. The MiniBMS control board was extracted, leaving room for a couple essential Orion BMS components. This includes a 12 volt DC power supply that provides a charging signal for the new Orion. It’s the TDK Lambda unit seen above in blue, mounted on the DIN rail to the right of the white heater power circuit fuse holder. Another essential component is a relay for the charger safety shutoff, visible in the lower right corner of the control box. A longer terminal bus was also included to provide routing for all of the new BMS signal wiring. Although better organized, the remaining items are the same, including the heater contactor at left, and fan speed switch snubber diodes at top right.

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wires.pins.diagramThe control box wiring is basic enough to warrant a simple flow diagram, rather than a full schematic. So I whipped one up in notepad, listing the box contents on one side, and all external connections on the other. My plan puts a 16-pin connector smack between the two, so I can easily connect and disconnect the control box when it needs servicing. Shown above are all of the control box connections, labeled, crimped and ready for hard-wiring.

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connector_spreadI really miss browsing a serious electronics store, with aisles of really cool lights, switches, relays, and connectors. A place where you can see and touch any component before you buy it. Conversely, wading online through the myriad of connectors at sites like Mouser, DigiKey, McMaster-Carr, Newark, Allied and Del City was an abstract and tedious undertaking. Unless you stumble on a complete connector kit, it requires locating both the male and female sides of the connector, and finding the correct pins and sockets to match them. Not knowing what to expect, I ordered a couple different connectors, hoping at least one would fit the bill. As luck would have it, either of the 16-pin connectors shown above are perfect for the main artery of the BMS, connecting the Orion to the control box and the rest of the car.

As a public service, I’m listing the connectors here:

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molex_assembled_heldIn my hand above is the male side of the Molex connector packed with all wires from the control box, including signal and control paths for the BMS charge circuits, and connections for the heater core and fan speed circuits. The female half shown beneath it will be connected to the car side, with recessed sockets that will isolate and protect the hot power leads carrying ignition and accessory power.

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molex_female_populatedHere is the female half of the Molex connector wired into the car-side harness, which includes the ignition lead, 12 volt DC power from the DC/DC converter and auxiliary battery, chassis ground, heater fan speed switch leads, and the Orion BMS harness. To avoid full pack voltage intermingling with all the other sensitive BMS wiring, the pack voltage sensor leads from the BMS will connect separately outside the box.

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all_carside_plugsThe remaining car-side leads are routed through various connectors, so each component can easily be disconnected for servicing, diagnosis, removal, and/or replacement. The rest of this paragraph is for EV builders who are truly interested in the above shot. If that’s not you, the following will be pretty boring. The female 16-pin Molex connector is shown above with the white mating face inserted. The 2-pin white Molex connectors at top and bottom allow the Orion to sense pack voltage. The black cord entering from the upper left routes live and neutral AC power leads from the J1772 charge receptacle to the TDK DC power supply, providing the BMS charge signal and powering the auxiliary cooling fan. The light blue terminals at middle right are the positive and ground connections for the same fan. Lastly, the big, flat Anderson connector in the middle delivers full pack voltage to the heater core and contactor. Kudos if you read this far; you are truly dedicated.

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box_w_plug2 The Orion is too pricey to risk hooking up without a final inspection. I double-checked all wiring against my schematics and flow diagrams, and tested the circuits one-by-one. It was very exciting watching everything check out, although this description may get technical. I started by disconnecting the charger and plugging the car in, sending AC to just the TDK power supply and confirming its correct output . Then I connected the TDK output to the DC fan to check its polarity and proper functioning. I used the same output to confirm the operation of the BMS charger safety relay. Click-click. I disabled the emergency shutoff, completing the battery pack power circuit, and then fired up the Elcon charger. Touching and separating the charger DIN wires toggled the Elcon ON and OFF. Happy times. Finally, I mated all connectors and mounted the control box on its support bracket in the trunk. Please take special notice of the installed 16-pin Molex at the lower right. There’s a lot of geek pride wrapped up in it.

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celltap_check2Before the cell taps are plugged into the BMS unit, they need to be tested to make sure all 36 leads are connected properly. If any wires are crossed, the Orion could malfunction and even suffer severe internal damage. Ewert Energy, maker of the Orion, rents out an electronic tap validation tool that plugs directly into each connector and confirms the proper polarity and serial order of each cell’s tap wire. However, Ewert also outlines a process in their install manual that forgoes the validation tool and operates directly on individual connector pins with a multimeter. With the black probe of the meter tied directly to the most negative terminal of the pack, each of the connector positions can be tested with the positive probe for cumulative pack voltage, adding ~3.4 volts per cell sequentially through the tap lead connectors until full pack voltage is reached. After running this sequence a few times for good measure, I confirmed all tap leads were in the proper polarity and sequence. More happy times.

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orion_final_installHere is the Orion fully installed under the right-side dash between the center console and glovebox. It’s hidden pretty well, and only the leading corner of the cooling fins are visible from the passenger seat. The cell tap bundles are seen connecting to the Orion from the right, traveling to the battery packs either through the firewall or heating ducts. The main I/O, pack voltage sensor, and current sensor connectors have been plugged into the opposite side of the Orion. The unused parts of the I/O harness were heat-shunk, coiled, and dropped into the console cavity. I didn’t want to delete them because they may eventually find a future use. Two shielded pairs remain for the CAN interface, which will be covered in the next post.

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dc_fan_speakerA very important addition is this auxiliary fan that will increase circulation around the charger. It’s mounted under the dashboard on the passenger heater port above the speaker, and will draw air across the charger’s cooling fins from the matching port on the driver side. This will prevent thermal events that cause the charger to throttle back and undercharge the pack. The choice was between a 12 volt DC or a dual-voltage AC fan. The AC fan moves more air (47CFM) and will run directly off the charger supply current, but is fairly noisy at 48DB. The DC fan is a tad quieter at 34DB, pushes slightly less air (42CFM) and would run off the same 12 volt supply as the BMS charge signal. Because the DC fan is quieter, it won out. If I need more oomph, I can easily swap in the AC fan at a future date. Maybe I’ll get schmancy one day and add a thermistor that will stop the fan when the charger shuts off.

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8 Responses to “Battery Management Rethunk”

  1. Can’t wait to see the touch-screen console…

  2. ditto…thank you for sharing.

  3. Can’t wait to see the touch-screen console (your adding)…because… I LOVE the graphical representation of data. I just get mesmerized by the graphs and bars that show the efficiency of the hybrid car, such as with the Prius. Nothing like stats, graphs and charts to remind & rationalize the buyer of why they spent the extra $$$$$ & reinforce the perceived value. Exaggerating perception is key!

  4. I’m also using the Orion BMS to manage my LiFePO4 battery bank (195AH compared to your 180AH). One of the things I still need to add, however, is a charge safety relay (I also use an Elcon charger). I looked at your parts list and what is listed doesn’t match up with what you have pictured. You show a solid state relay (Solid State AC Relay SSR with heat sink) in your parts list, but the pictures clearly show something different being used.

    What relay switch did you use, and did you also need to include a separate pull-up relay between that and the Orion BMS?

    • Hey Patrick,

      Ignore the solid state relay from the earlier parts list. That original SSR was going to externally cut AC power to the charger, but when I discovered that the Elcon has a built-in safety disable input, the design changed.

      Here is the exact relay I used, as recommended by Ewert: Omron G8P-1A2T-F DC12.

      The relay needs external 12VDC power as long as the charger is on, which supplies signal to the built-in cutoff on the Elcon (red & green DIN plug wires). The lower amp driving signal comes directly to the relay from Orion connector pin #6. This way, when the Orion decides that your pack is charged, it cuts the signal from pin #6, the relay opens, the Elcon loses the 12V signal, and the charger shuts off. This way, you can program the Orion to charge the pack to whatever level you desire.

      (This is mostly from memory, so I would double-check everything I’ve said here!)

      Cheers,
      Mark

  5. […] *** NOTE – After some end-user issues with the MiniBMS, I decided to pop the extra cash for the Orion BMS. That entry is here. […]

  6. […] *** NOTE – The MiniBMS performed perfectly as advertised, but at a later date I decided I wanted access to more pack data with a better display option, so decided to pop the extra cash for the Orion BMS. That entry is here. […]


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