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I heard a rumor at InsightFest-Columbus that someone has probed the Fit BCM board with some slight success. I overheard a discussion about this board in which Mudder was involved, and he suggested half of that board was immediately discard-able and the other half could be probed easily and rather quickly by a knowledgeable, experienced person with resources in order to figure out if / how this board might be utilized in the insight with its parent LTO pack to manage its voltage. Does anyone have a knowledge of this?
 

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Yes - I was analyzing some of these boards last year and came to the same conclusion. The board has two circuits almost entirely separated save for an optocoupler. One side of the board appears to be primarily for CAN communication while the vehicle is on. The other appears to be the actual battery management and balancing circuitry.

If I remember correctly it appeared the battery management side was powered entirely by the battery, and I have a theory that it will keep the battery internally balanced as long as it is present and working, without any input the the CANBus.

One of the boards I had led me to believe it was doing exactly this. The other wasn't, but I believe it to have been broken - possibly the reason the battery was pulled.
 

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Yes, battery management side appears to be entirely self-contained and powered by battery section it is monitoring. The chip numbers don't relate to any shipping product, but just looking at the package suggested to me that it is a rebadged TI part. It certainly isn't an LTC6804... anywho, at some point I'll pin out that IC's pins based on how the PCB is configured, and then I'll use that info to find whatever BMS chip has the same pinout. Note that that IC has a really strange TSSOP configuration: it's missing six total pins, which aren't manually broken off, but rather they were never there in the first place.

The big thing is that this (presently) unknown IC has an unpopulated programming header, which almost certainly uses a standard SPI (or isoSPI) interface. If we can figure out that comm bus, the actual IC maker likely won't matter. The easiest way to do this would be to populate that missing connector and then watch the data sent across the port while the battery is in its OEM host. To do that, someone will need to get their hands on the OEM car.
 

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Very useful info as the BMS could be left attached to the packs to at least keep them balanced as a block.

Tim's LTO car which we are hopefully finishing today had very well balanced blocks which also suggest this is correct..

The only issue might be very long term storage...As there must be a very small parasitic load if the BMS is active when connected.

If the LTO BMS remains fitted, then simply monitoring block voltages with the BCM Replacer taps should give a good picture of the overall balance etc..
 

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If assuming pack level balancing is automatic when using the Fit BMS boards, two potential concerns come to mind. Of course this is purely hypothetical at the moment.

It may be possible for 24-cell packs to balance to different voltages.

If one were to use a half pack in the 84 cell configuration, possibly the balance wouldn't work on the 12 cell pack.
 
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