Paging Norm Dick

Discussion in 'Prius PHEV Plug-In Modifications' started by clue--less, Sep 30, 2020.

  1. clue--less

    clue--less New Member

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    I know this is a long shot but I try it anyway, maybe Norm, the creator of the excellent conversion equipment BMS+ still reads these fora. Or perhaps someone else can help us.

    We are building an experimental Vehicle-to-Grid solution, including both EVSE and the on–board unit. Budget is limited so we are opting for a 2007 Prius conversion. We want to use Norm's BMS+2 with a parallel pack built out of 18650 cells in a 70S7P configutation.

    We read Norm's suggestion on using the BMS+ in this setup as described on hybridinterfaces BMSnew html

    Second the more DIY approach of a parallel pack of typically 70 or so Lithium cells allows EV and mixed mode operation to the same (if not better) performance enjoyed by BMS+ and parallel Nimh packs. The OEM pack actually runs cooler than a standard Prius due to the current sharing and EV mode can be continuous at much higher current flows. The main difference is that a contactor is engaged during READY mode so that the OEM pack is no longer charged during house charging, thus avoiding any possibility of overheating it. With the correct number of lithium cells, charging them to near 100% involves a higher voltage than the OEM pack could stand. Once fully charged and connected via the contactor, an initial inrush current of <50A flows for under a minute which does not cause OEM heating and operation continues as 2 parallel packs until both have dropped to typically 210v at which point PHEV operation is discontinued until the pack can be recharged. At all times, full regen is allowed for both OEM and added pack

    My questions are these:
    1) Can I use the Tyco Kilovac EV200 contactor with the BMS+? It has a holding current of 130mA.
    2) When the parallel 18650 battery pack is fully charged and the car is in READY mode, the BMS+ engages the contactor (initial inrush current of <50A) doesn't it hurt the OEM battery? My battery pack consists of 18650 cells in 70S7P config.

    Many thanks for the kind response.
     
  2. planetaire

    planetaire Plug in 20 kWh 85 km/h or > 208km range

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    Hello,

    18650 is just a cell size. But they can be Lifepo4 or other chemistry.
    The cell/battery max voltage will not be the same.
    If Lifepo4 the max will be 70*3.65 = 255 Volts falling quickly after charging for example 70*2.40 = 238 Volts.
    If NCM or other it can be 70*4.1 = 287 Volts. LTO will have a lower voltage.

    287 Volts is much too high in my opinion, don't go over 240 Volts if using bms2 and the oem ecu
    The higher this voltage will be, the higher will be the amperage between the 2 packs, 50A is just a sample. It can be much more.

    You have to add the two lower IR (internal resistance) possible of the 2 packs in the higher temperature, usually in summer. Use the 2 pack delta voltage and you will have the max amperage. It will be a bit reduced because you will add a HRC fuse beetwen the 2 packs.
    That amperage must be possible during charging for the nimh pack and discharging for the 18650 pack.

    You should consider also cold temperature condition and check if the 2 packs can handle the inter pack current. See their datasheet.

    A+
     
  3. clue--less

    clue--less New Member

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    Thanks for the reply. I just registered the account and I can't post links, this is the actual cell:
    samsung inr18650 29e on the page eu.nkon.nl
     
  4. planetaire

    planetaire Plug in 20 kWh 85 km/h or > 208km range

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    These cells are NMC (LI Ni Mn Co). So their range is 4.1 Volts - 3 Volts (4.2 Volts would reduce cycle life)
    So 70S is too much, max voltage would be 287 Volts. Don't go over 240 V.
    And 7P is really not enough, you must to handle up to 100-125 A.

    A+
     
  5. clue--less

    clue--less New Member

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    These guys in Finland use 68 Nissan Leaf cells: pistokehybridi fi prius-konversio html
    Here 274V is recommended: priuschat com threads diy-plug-in-conversion-gen1-prius 147304
    Norm has also mentioned that but I cant find it now.
    The Enginer kit (4kW) has a steady current of 14Amps which is either charging the OEM battery pack or powering the drivetrain.

    Where do you get your numbers (240V/125A) from?
     
  6. planetaire

    planetaire Plug in 20 kWh 85 km/h or > 208km range

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    #6 planetaire, Oct 12, 2020
    Last edited: Oct 12, 2020