Currently Available Prius PHEV Mods?

Discussion in 'Gen 2 Prius Accessories & Modifications' started by pyromaster114, Jul 10, 2019.

  1. pyromaster114

    pyromaster114 New Member

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    I know there are reasons why the PHEV market has kind of dried up. But that's kind of a shame, I feel.
    With battery technology improving, and thus the potential all-electric range improving for a converted vehicle, there's absolutely no reason that there should not be hardware available to do this.

    And I have a great idea as to how to get it done, or at least I think, and wanted to get some feedback from people who might be more familiar with the car's systems than me.

    So, a Prius (Gen 2 and Gen 3, as I understand) has 14 'blocks' that the BMS pays attention to, which are each composed of 2 modules, each containing 6 NiMH cells.
    This gives us two options for creating a conversion kit, which require ABSOLUTELY NO DC-DC converter, and no (or very limited) ECU hacking.

    First off, we could do the obvious thing, and take (now extremely affordable) Lithium Ion cells, and make a series of 64 of them. Charge them to 3.9 Volts per Cell, and this gives us a pack voltage of 249.6 Volts. (And they'd be discharged down to about ~3.5 - 3.6 Volts per Cell, or about 230.4 Volts for the pack.)
    This pack is put in parallel (before the contactors) with the factory NiMH pack, separated by some high voltage relays that can be disengaged by the add-on pack BMS in case of over or under voltage.
    The add-on pack would keep the stock NiMH pack 'full' ('in the green' on the display in the gen 2) where the vehicle is inclined to try and activate 'EV mode' (which does exist in the Gen 2, just can't be activated manually, apparently... 0.o?) and not ignite the ICE until the add-on pack's BMS cut the high voltage relays connecting the add-on pack when it's 'empty'.

    This approach has some problems, namely that if the add-on pack has been emptied, and the car is parked with a low-charge state stock battery, serious battery-battery current flow could happen when the stock battery pack was reconnected the next morning to a now fully-charged add-on pack.
    This could potentially be solved by allowing a secondary path between the two packs to exist while charging, but with a resistor in-line, preventing the huge and dangerous / damaging current flow until the packs were at a fairly similar voltage.


    Second, and a bit more expensive and more hardware-modification intensive, we could take the individual block approach, completely replacing the factory cells with LiFePO4 cells. Each block would contain say, 6 LiFePO4 cells.
    With a minimum discharge voltage of 2 volts per cell, and a maximum charge of 3.2 volts per cell, this will actually exceed what the BMS computer thinks is an acceptable range for each block, thus allowing the stock BMS to prevent the batteries from over-charging, or for that matter, over-discharging.
    The system could treat them like the stock pack, and they'd sit in the middle of their voltage range (~2.3 - 3.0 Volts per Cell) forever, and should last an insane amount of time like this.
    One exception of course, would simply be that this add-on pack would be many times the size of the Prius' stock battery in terms of capacity, and would have an AC charger attached to it so that when the vehicle was parked, it could be charged from a standard 120 Volt (or 240 volt) outlet, using a high-voltage charger.

    The problem with this approach, while extremely simple electrically and ECU-wise, is the fact that we may run into the Prius' ECU not 'using' the whole pack's capacity, because it would think 'oh crap, I need to charge this' when the battery was only ~50% discharged.
    This could possibly be solved if we could do a small amount of hacking and activate this supposedly-hidden 'EV mode' in the Gen 2's, for example, allowing the vehicle to not ignite the ICE until the pack was closer to ~30% state of charge.
    The other problem of course, which is easy to solve, is that there would need to be a good failsafe BMS attached to the LiFePO4 pack, to prevent over-charging or over-discharging, because there are safety concerns (though not as much with other Lithium chemistry) if such a pack were to go over-voltage. There'd simply have to be a BMS that could keep an eye on cell voltages and just cut the pack out entirely. Sure, you'd end up with a dead vehicle until you repaired the pack, but I've learned that's far from impossible with a stock Prius pack, as mine is currently waiting on parts to (hopefully) get the thing running again.


    Personally, I'd be really interested in knowing some more about how the prius acts at different voltage ranges of the stock pack, because option 2 here sounds like the holy-grail of Gen 2 (and maybe 3?) Prius modification. Replacing an ancient NiMH chemistry with a pretty much literal drop-in replacement, while potentially adding PHEV functionality.
    Any help and feedback is appreciated, and sorry for the long-winded post!
     
  2. doctor126

    doctor126 New Member

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    im following..
     
  3. bisco

    bisco cookie crumbler

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    welcome!

    sorry, no one here has the expertise for this, except to tell you why it can't be done. (of course it can)
    . as you said, it ran out of steam years ago.
     
  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I'd think it would be a heck of a lot simpler to stay isolated from the native HV system and add a powered rear axle. Then you just need to harmonize the throttle & direction select- maybe even simplify that by only having it active for forward motion.

    That way you aren't fighting the Prius native stuff while still getting a pretty big pluggy benefit.

    Still wouldn't be easy, but it would be a heck of a lot easier than trying to get in the middle of all the hybrid stuff.
     
  5. donbright

    donbright Junior Member

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    I do still find something very interesting about this. plain Prius gen 2 and gen 3 battery capacity is 1.310 kilowatt hours. So. If we disregard a lot of details for a moment, and simply look at price per kilowatt hour, let's compare options for someone with a Prius and a dead HV battery:

    Dealership new OEM box + install, about $5,000.00 or $3,816.79 per kwh
    Texashybridbatteries new box + install: $2,250.00, or $1,717.56 per kwh
    Newpriusbatteries cylindrical DIY battery kit: $1,600.00, or $1,221.37 per kwh
    Mythical dealership new box DIY install: $1,600.00 or $1,221.37 per kwh
    Texashybridbatteries rebuilt used + install: $950.00 or $725.00 per kwh

    Now let's look at some Lithium battery packs (which currently lack the necessary electronics):

    New LG Chem pack from EV West: $735.00 for 2.6kwh, or $282.69 per kwh
    Used Tesla module from EV West: $1,580.00 for 5.3 kwh, or $298.11 per kwh
    Used Tesla module from rando website: $1,150.00 for 5.2 kwh, or $221.00 per kwh
    New Panasonic 18650s from EV West: $490.00 for 180 cells,*3.03Ah*3.6v~=1.96 kwh or about $249.56 per kwh
    Elon Musk and Panasonic apparently have a goal build packs for $100.00 per kwh by 2020

    So if you want to build a 1.3 kwh battery out of Lithium, your battery cell cost is theoretically already under $300.00 and going down every year, possibly to $130.00 by 2020. If that happens, it will literally cost you more to replace your broken AC vent covers than to buy the HV battery cells.

    So as an amateur my question is... can you build the electronics (charging, monitoring, regen, cooling) to integrate into the Prius for less than the difference in price? And can you keep it from starting an unquenchable Lithium fire like Rich Rebuilds did to Daisy the Disney car?
     
  6. bisco

    bisco cookie crumbler

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    absolutely (not me, but some really really smart electronics genius)
     
  7. donbright

    donbright Junior Member

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    I wonder if any of the old PHEV kits did any "faking" of signals to the Toyota BMS? Someting like this:

    bms.png

    If the magic box + wiring could be made for less than $220.00 then it would be competitive on price for a replacement of stock HV battery, possibly much lighter weight....and maybe a modular design would allow "upgrades" to PEHV or higher capacity...

    See also State of Charge | PriusChat
     
  8. bisco

    bisco cookie crumbler

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    i don't think there was much cost beyond batteries in the day's, and as you've said, batteries have come down considerably.
    there are plenty of old detailed threads here, but the one guy who really pulled it off kept everything secret
     
  9. SynEco@eVehicle.co.nz

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    You can parallel install a LiFePO4 pack with the existing pack. For 2004-2008 PRIUS we used a "man in the middle controller"
    that updated the SOC from the BMS CANbus to 90% SOC while PHEV pack had usable SOC . This forces the HEV ECU into "EV run mode" to pull the pack below 90% SOC.
    The controller is out of production but could make a run of these if we had sufficient folks to order the units???
     
  10. bisco

    bisco cookie crumbler

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    nice. i don't understand why more people aren't doing this. what about 2009?
     
  11. bisco

    bisco cookie crumbler

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    what say you, oh master of pyro?
     
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