Is adding a second battery possible?

Discussion in 'Prius PHEV Plug-In Modifications' started by hyp3rmil3r, Dec 22, 2019.

  1. hyp3rmil3r

    hyp3rmil3r Junior Member

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    I see tons of traction batteries pulled from priuses for sale. Is it possible to wire one in conjunction with the one I already have in my car for double the battery capacity? It may sound naive but it would be awesome to boost the cars ev capabilities.

    I’m looking for an inexpensive alternative to the insanely price PHEV kits in favor for something more diy friendly.
     
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I would never call such a project impossible but it would be a very, very tall order as a DIY project.

    Three points:

    1. If you want to do this for extreme bragging points and cool-factor? I wish you the best- this would be big. Conversely, if you want to do this to save time, money or other resources, I urge you to stop now. You will rapidly exceed the affordability of PHEVs already available, to say nothing of those coming soon, all without ever matching their capability.

    2. Even doubling a Prius battery is not in the same zipcode of battery capacity as a typical PHEV. A Prius battery has about 1.3kWh capacity. Most storebought PHEVs these days offer 8kWh and up. So I would (not very seriously) suggest adding 3-5 more HV batteries as a starter goal. Obviously that vastly complicates things and yet still doesn't make much of a PHEV range-wise.

    3. The Prius Prime PHEV also includes a trick clutch between the combustion engine and the transaxle. This device allows the car to drive at highway speeds using electric power exclusively without also forcing the engine to spin in deadhead mode. Your car doesn't have this clutch, so your electric-only efficiency would suffer badly above roughly 40mph.
     
  3. Rmay635703

    Rmay635703 Senior Member

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    Assuming you have a generic Prius NIMH you could just charge your battery up, reset the computer and on your commute the car would burn off some of the three to five EV miles you built up.

    understand this wears the battery out faster and may cause your car to freak out with CELs and other unenjoyable nonsense

    another method of mild range extension is modifying your 12 volt battery to be a 14 ish volt deep cycle, this shuts off the dcdc and drives 250-600 watts to your battery.
    take care not to exceed the cars maximum voltage while recharging (hard to do) and it does have a real effect on fuel economy similar to an alternator delete.

    in terms of having two NIMH batteries it’s a fire hazard so don’t bother.

    I recommend visiting ecomodder for actual real world mods that work to get better economy and not high hanging fruit that wastes time and money

    good luck
    Ryan
     
    #3 Rmay635703, Dec 23, 2019
    Last edited: Dec 23, 2019
  4. jerrymildred

    jerrymildred Senior Member

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    Even if you added enough batteries to have useful range, you'd still have the speed and acceleration limitations that would make the car unusable for anything more than residential speeds. The MGs and inverter don't have enough power handling capability for highway speeds nor can the MGs spin fast enough because of the gearing and construction.
     
  5. The Electric Me

    The Electric Me Go Speed Go!

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    It's Hybrid Synergy Drive....don't mess with the Synergy.
     
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  6. bisco

    bisco cookie crumbler

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    no
     
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  7. hyp3rmil3r

    hyp3rmil3r Junior Member

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    Sounds like an ultimately unrealistic idea. I didn’t realize I’d need an excess of multiple batteries to make a difference. Also the lack of the clutch on my gen 2 mentioned on the prius prime would be a big issue. Really im not concerned about ev only mode, id just like the car to run in electric mode more often increasing MPGs.

    For example the prime runs in EV mode if you want, or in hybrid mode you achieve far more MPGs than a standard prius since the battery is much stronger. Then again I suppose it has a much much larger battery than just two gen 2 batteries. Thanks everyone.
     
  8. sam spade 2

    sam spade 2 Senior Member

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    THIS.
    All the computer systems expect to see a certain HV battery in place.
    Having one that is drastically different would likely cause DRASTIC results.

    So the answer is: NO. Not practical.
     
  9. bisco

    bisco cookie crumbler

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    prime only achieves a small amount of mpg's over lift back, if you're not using wall power, and will not run in ev mode if the wall charge is used up.

    and yes, compared to lift back, prime battery is umongous
     
  10. ice9

    ice9 Member

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    IF it was possible, and I won't say that it isn't, I would expect the only practical way of doing it would be to add a duplicate battery that could be electrically switched/swapped.
     
  11. Marine Ray

    Marine Ray Senior Member

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    You could alway get a Prius Prime :)
     
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  12. hyp3rmil3r

    hyp3rmil3r Junior Member

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    Seems like there’s two responses here:

    1. DONT mess with the sanctity of your $875 224k mile prius its PERFECT!

    2. Hey it’s possible but probably not practical.

    I’d like to thank the type 2 responses for your measured input haha!

    In response to the type 1’s... guys my car is a junker. I’m happy to modify it and would like to if there are easy budget friendly modifications to increase mpgs. All I was asking is if there was an obvious easy way to add battery capacity. No need to get frazzled. I won’t be adding a battery after reading these posts, so rest assured knowing my precious synergy will remain untouched!
     
  13. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Think about that. How do you run in electric mode? By supplying power from a charged battery. How do you charge the battery? By running the engine on gasoline, or by harvesting momentum. How do you harvest the momentum? Get the car rolling, then apply regenerative brakes. How do you get the car rolling? <loop to beginning>

    All of the energy comes in through the gas filler, and then some of it gets recycled via the regen function. But only some, due to efficiency loss. Hypothetically you could make a Prius even more fuel efficient by eliminating the electric end of the hybrid powertrain and just coupling the engine to the wheels. Less weight to carry and no conversion losses in the electrics. Downside: it would be almost undrivable and hopelessly incompatible with traffic and drivers' expectations.

    In a sense, the real secret of Prius fuel efficiency is the tiny gas engine. It's too weak to power a Prius-sized car alone, but when combined with the electrics of the HSD, it gains driveability.
     
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  14. hyp3rmil3r

    hyp3rmil3r Junior Member

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    I would have charged the battery via grid much like a prime, really though I’m not looking for any more replies here. Mods can feel free to delete thanks.
     
  15. Rmay635703

    Rmay635703 Senior Member

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    no worries

    nothing stops you from charging that battery for a small economy gain.

    many grid charge batteries to get life out of failing packs.

    and again

    ecomodder.com

    Darin, Neil B and Ben Nelson have all been there done that, start a thread there
     
  16. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Some electrical issues. If the batteries are in parallel you need twice the current to charge them, you don't have it.
    If the batteries are in series you need twice the voltage to charge them, you don't have that, and it is unlikely you can get it.

    The other choice is PHEV one battery, so you have more current. At that point the cheapest way it to buy a PHEV.

    There were a whole flurry of kits to do this in 2004, but those companies are went broke paying out liability claims.
     
  17. sam spade 2

    sam spade 2 Senior Member

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    OR you need the same current for twice as long. ;)
     
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