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 Junior 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???
     
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  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?
     
  12. SynEco@eVehicle.co.nz

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    The data was taken of the CANbus post 2008/9 (genIII)
     
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  13. doctor126

    doctor126 Junior Member

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    i am wondering how much is this?
     
  14. Ragnorok

    Ragnorok New Member

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    I would expect doing this "right" would require lots and lots of data regarding how the BMS interacts with the pack. Once enough of that is obtained, by definition of enough, it should be possible to "shim" it with a SoC to work with about anything. No idea how to go about that. Probably start with a complete shop manual and read anything that seemed related to battery management, and hope that same manual has a run-down of the CAN bus data. Patch something in, getting parallel data from the BMS and direct measurement, which would probably require designing some high impendance sensing. Drive around until "enough" data is acquired. Start off with some standard 12v batteries in the back, set up to replace the 1.3kwh NiMH pack via the "shim". I say 12v because they're less likely to burst into flames if one is a bit aggresive with their electrons. Work the kinks out with that setup. Swap in whatever battery/tech you want. Done. Easy Peasy. ROFL

    After typing all that I see some guy in Oz has done something like this already. See:

    BMS plus or alternative | PriusChat

    should have looked first...
    - Rags
     
  15. bisco

    bisco cookie crumbler

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    yup, it's no mean feat
     
  16. ericbecky

    ericbecky Hybrid Battery Hero

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    I'd be interested in something like this.
    Is there a place where I could read more about it?
     
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  17. richmke

    richmke Junior Member

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    I wouldn't put a relay to connect/disconnect the Additional Battery Pack (ABP). When you put the pack back on-line, you have to make sure there is virtually no voltage differential between the ABP and the Traction Battery. Otherwise, you are looking at sparks, and lots of power flowing between the batteries.

    The Gen II prius has EV Mode, but it was not included in USA versions of the Prius. Here are instructions to add the EV Mode button:
    http://www.calcars.org/prius-evbutton-install.pdf

    Once you have the EV Mode button, you can add the ABP in parallel. Once you turn off EV mode, the ICE will charge both battery packs. I have no idea how the charging circuit will react to the additional capacity. Maybe it will think you have weak cells.

    Instead of putting the ABP in Parallel with the Traction Battery, you could use a Transfer Switch, so only 1 pack is connected at a time. When the ABP is drained, you switch back to the Traction Battery and turn off EV mode. If you want to be cute, you can use circuits on the ABP side to sense when the ABP battery is connected, and flip a relay to turn on EV mode.

    Note: The Transfer Switch has to be designed so that there is no chance that both batteries are connected at the same time, even if only for a moment.

    Note 2: I have no idea how the ECU will respond when the Traction Battery is disconnected - individual voltages of each cell does not match the total battery power it sees. For example, you could have a charged Traction Battery, and the cells are showing 16 volts, which totals 224v for the pack. As you drain the ABP, the voltage available could drop to 209v. It might confuse the ECU.
     
  18. love2drivefaster

    love2drivefaster Junior Member

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    What about just stripping the ICE & Hybrid and converting to straight electric? Has anyone done this yet?
     
  19. Ragnorok

    Ragnorok New Member

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    This is something I've been wondering about, but the 34mph limit is a little annoying. Why doesn't it go to 42mph like it normally does? Only about four miles of my trip has speed limits that low, and I'm typically already doing EV those places by using the throttle.

    What'd I'd really like is a way to tell it not to use the ICE, even if it has to slow down to keep from stressing the battery. Ofc if the battery gets too low, hit the ICE, but if it's half full and I have 100m where I'd like to force Wembley to use electrons and shed minimal momentum, that would be cool.
     
  20. donbright

    donbright Junior Member

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    Saw a fascinating snippet today, in an article by Bengt Halvorson at Green Car Reports ( Lithium-ion vs. nickel-metal hydride: Toyota still likes both for its hybrids )

    "According to Prius chief engineer Shoichi Kaneko, in an interview this past week at the LA Auto Show, most of Toyota’s current hybrid lineup are capable of easily trading off between the two battery types"​

    Now... it made me wonder. What exactly does he mean by trading off? Which generation of Prius is capable of easily trading off, and how does it accomplish this? And how feasible is it for a customer to flip the car back and forth between the two chemistries?

    Is it build into the hardware of the car, and they plug and switch out the battery pack and battery computer? Then reprogram the car to use which ever battery type they installed? At the inverter level, I am wondering if the inverter has two operating modes - one for LiON and one for NiMH? How does this get triggered or commanded?

    Or does the car require a completely different inverter and ECU?

    I guess the question for Gen 2 - can you "back port" the inverter and LiON batteries from a Gen4 to a Gen2? Along with perhaps the plugin pieces from a Prius Prime?
     
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