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Why Can't Toyota's Plug-In Prius Recharge Its Larger Battery?

 
5,506 views May 11, 2010
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prototype 2012 Toyota Prius Plug-In Hybrid, April 2010

2010 Toyota Prius Plug-In Hybrid, 2009 Los Angeles Auto Show

2010 Toyota Prius Plug-In Hybrid, 2009 Los Angeles Auto Show

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Toyota has come under some fire from electric-vehicle enthusiasts for what some perceive as a grudging, halfhearted approach to building vehicles that plug in.

Its first U.S.-market plug-in vehicle--not including a thousand or so RAV4 electric crossovers a decade ago--will be the 2012 Toyota Prius Plug-In Hybrid.

It's a modified Prius with a larger 5-kilowatt-hour lithium-ion battery pack that recharges on wall current, giving up to 12 miles of electric range at speeds as high as 62 miles per hour. The pack is, in fact, three packs: a main one plus two sub-packs.

Toyota has built 600 Prius Plug-In Hybrid prototypes. We'll see 150 of them in the U.S., with 200 to be deployed in Europe. The U.S. cars are now being distributed to the fleets that will test them over the next year.

Last month, we test-drove a 2012 Prius Plug-In Hybrid prototype. And we were shocked to learn that it does not use regenerative braking to recharge the two extra battery packs that provide the added electric range.

In other words, once the added battery capacity has discharged, the Prius Plug-In behaves just like a plain old 2010 Prius hybrid until it's plugged in again--using only its main pack, which holds the same 1.6 kWh of energy, slightly more than the 1.3 kWh of as a standard nickel-metal-hydride Prius pack.

When we questioned Toyota about this, Dave Lee (a former technical trainer on the program) said that it was occasionally possible to top up the extra packs for 1 or 2 miles of range, if the two auxiliary packs were still largely charged.

But Lee admitted that the ability to recharge the larger pack on the fly "just wasn't the way they designed it."

Why? He said a Toyota engineer told the technical trainers that the battery relays hadn't been designed for repeated opening and closing during driving.

Hmmmmmmmm. This seems odd, to say the least.

Whether or not the Prius Plug-In competes against cars with much longer electric ranges, like the 2011 Nissan Leaf (100 miles) or 2011 Chevrolet Volt (40 miles), it seems wasteful not to provide as much electric driving as possible from the packs it carries around.

And in fact, "I would anticipate us making a change," Lee said carefully. "That would make sense" to use regenerative braking for the added packs, rather than switching on the engine to use up the current.

"What we have in this car," he said, "may not be what we offer going forward."

Let us hope.


HI-RES GALLERY: prototype 2012 Toyota Prius Plug-In Hybrid, April 2010




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Comments (18)

  1. By Desertstraw Posted: 5/11/2010 8:47am PDT

    Advice to Toyota. Start building Rav4 Electrics. Experience has shown that they were great vehicles.
    As one of the first buyers of the Prius, I am not considering another. They were fine cars for their time. I am on the list for a Nissan Leaf but will consider a better electric car if someone sells one.
     
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  2. By usbseawolf2000 Posted: 5/11/2010 9:22am PDT

    "In other words, once the added battery capacity has discharged, the Prius Plug-In behaves just like a plain old 2010 Prius hybrid until it's plugged in again--using only its main pack, which holds the same 1.6 kWh of energy as a standard nickel-metal-hydride Prius pack."
    That statement is inaccurate. PHV Prius has 5.2kWh pack. Each pack has 1.73 kWh (5.2 divided by 3). The standard Prius with NiMH pack has 1.31 kWh.
    PHV Prius in hybrid mode using the Lithium main pack still has 32% bigger battery to store more regen.
     
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  3. john_v avatar John Voelcker Posted: 5/11/2010 10:01am PDT

    @usbseawolf2000: I'll double-check those energy capacity figures. Another factor that I didn't include is that the Li-ion pack uses more of its charge capacity, from roughly 20-80% instead of 30-70% for the NiMH, which gives it more *effective* energy capacity.
    But I wouldn't read too much into any of these figures since, as the article notes, the Prius Plug-In that Toyota sells here may have a different pack arrangement and, most likely, a different chemistry of Li-ion cells too:
    http://www.greencarreports.com/blog/1041538_why-the-2010-toyota-prius-doesnt-have-a-lithium-ion-battery
     
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  4. By Bob Posted: 5/11/2010 12:38pm PDT

    Battery cars are a waste of recources and loose charge capacity after so many charges. Which means as the years go on the less MPG you will get. Diesel is the way to go !!! Also if the prius is so great then why did Toyota stop producing the Echo which got similar MPG with no BATTERY !! Its all hype to make the public think your doing something better for the environment when infact your actually getting shafted in the bum.
     
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  5. By  Doug Korthof Posted: 5/11/2010 5:24pm PDT

    The secret is that Toyota was slapped with a lawsuit for using NiMH batteries, due to cooperation between Chevron and GM, and Toyota is unwilling to actually sell a plug-in car using the only battery proven to work, NiMH, until Chevron's patent rights expire in 2015. It's true that Chevron sold part of the rights to Samsung/Bosch last year, but they retained their stranglehold on Toyota, which still forbids Toyota from using NiMH on plug-in cars until 2015.
     
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  6. By Paul Posted: 5/11/2010 5:24pm PDT

    OBVIOUSLY Toyota are still paranoid about high cycle rates on their Lithium Ion cells. (lack of product confidence is the EXACT reason they are so late with a commercial plug-in and .... why they are now doing PR about an FC car in 2015) Panasonic Li-ion batteries must be rubbish.
     
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  7. By  doug korthof Posted: 5/11/2010 5:30pm PDT

    Bob, your opinion is a mistake common to many. Our Toyota RAV4-EV, last sold in Nov., 2002, is still driving over 100 miles range over 100K miles. But let's look at the life-cycle cost. Building the fleet of NiMH RAV4-EV involves resources. But after the batteries wear out, perhaps 100K miles or 200K miles, or more, they can easily be remelted down using THE SAME MATERIALS, no new mining needed. So in reality, the price of the batteries is vanishingly low; if, as CARB estimated in 2000, a NiMH pack in mass production would cost $8500 new, that's less than 8 cents per mile -- and the electric is free, if you have a home rooftop solar system, a I do. After that time, the old batteries, with all the alloys and materials, can be remelted for significantly less than $8500 -- perhaps $1000 or less.
     
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  8. By  Doug Korthof Posted: 5/11/2010 5:59pm PDT

    John, the NiMH Prius pack is 1.3 kWh; at 288v nominal, that's about 4 amp/hours, well within the bounds of Chevron's patent rule (no NiMH pack larger than 10 amp/hours). But if they are using Lithium, it may be larger; most likely they will only cycle it from 50% to 80% to reduce wear and prolong battery life, as they do currently, no matter whether it's Li or NiMH.
    The reason for not recharging the Li battery pack via regen braking is simple: Toyota is afraid of battery degradation via "mini-cycles".
    What they call a "cycle" is from 100% to 0%, which puts a strain on any deep-cycle battery. That's why we generally fill only to 95% or so and only discharge to 20% or so; but sometimes we go beyond those limits due to the exigencies of driving, or because we want to level the battery pack.
    There are hundreds of "mini-cycles", when you go up a hill or accelerate, you draw down from the battery pack; when regenerating, you get most of that back. That's a "mini-cycle" every time you start up (and stop).
    Toyota may be concerned that this "mini-cycling" would kill the battery prematurely; indicating once again that Toyota doesn't think Lithium is ready for 100K-plus driving.
    Supposedly, there is a LEAF with over 180K on the same pack, so maybe Toyota is wrong. I hope so.
    By restricting recharging of the additional packs to the wall-charging events, they maximize the number of cycles. NiMH doesn't have this problem in the RAV4-EV, of course.
     
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  9. john_v avatar John Voelcker Posted: 5/12/2010 1:30am PDT

    @Doug et al: Interesting and contentious comment stream. I can add that Toyota told me they cycle the Li-ion packs in the current design of the Prius Plug-In from roughly 20 to 80 percent, giving them a wider State of Charge (SoC) range than the current NiMH pack in the standard Prius, which is roughly 30 to 70 percent. And I did, btw, confirm that the standard Prius pack is 1.3 kWh and have changed the story accordingly; my error, for which I apologize.
     
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  10. By usbseawolf2000 Posted: 5/12/2010 7:06am PDT

    John,
    PHV Prius main pack has 1.73 kWh, not 1.6 kWh.
    We can find out the usable capacity from the information given by Toyota, 60% for Lithum and 40% for NiMH.
    Lithium: 1.73 kWh x 0.6 = 1.04 kWh (usable)
    NiMH: 1.31 kWh x 0.4 = 0.52 kWh (usable)
    As you can see, PHV Prius in hybrid mode can store about twice more energy in hybrid mode than a regular Prius.
     
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  11. By richard schumacher Posted: 5/12/2010 1:22pm PDT

    How could the car know when it was about to be parked near a recharge point, and thus that it should drain the plug-in batteries so that they can accept a nice non-fossil-carbon charge? (You *do* have a non-fossil source of electricity with which to recharge them, right? Otherwise the whole exercise is pointless from a global warming perspective.) Simpler to just use 'em up immediately and then drag them around.
     
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  12. By richard schumacher Posted: 5/12/2010 2:06pm PDT

    Musing further: the usual non-plugin battery is already about as large as it needs to be, enough to hold the energy of one launch to about 60 MPH. Making it bigger might improve fuel economy fractionally or increase battery life, but all of that energy would ultimately still come from the fuel. In contrast a plugin-only battery guarantees a more significant reduction in gasoline consumption and therefore a greater increase in MPGs. Whether that also results in a net reduction of fossil-derived CO2 depends on what the user plugs it into.
     
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  13. By walter lee Posted: 5/12/2010 4:54pm PDT

    Why cant "mini-cycle" charges be temporarily aggregated fed back to the seconardary traction batteries at a later date?
     
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  14. john_v avatar John Voelcker Posted: 5/12/2010 6:18pm PDT

    @Richard Schumacher (re/comment # 11): Actually, even if the battery recharges using grid power that is NOT from non-fossil energy, the carbon profile is lower for the average U.S. grid and all but a few edge cases (e.g. North Dakota's entirely coal-fired grid) even against a 50-mpg combustion vehicle. (See much-cited EPRI-NRDC study of 2-3 years ago.) So the whole exercise is NOT "pointless from a global warming perspective." Put another way, don't set up the perfect to be the enemy of the good.
     
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  15. fb_1376616026 avatar Doug Korthof Posted: 5/13/2010 9:21am PDT

    Excellent answer to the "powered by coal" argument. We hear this so many times...ironically, when talking about how to charge up EVs, all the electric seems to come from coal, but when making Hydrogen, they claim all the electric comes from solar. Amazing how those electrons know what to do and where to go! In reality, the upstream costs of oil dwarf any cost of electric you can name.
    Just the cost of refining, in energy alone, is 12% of the energy in oil. That 12%, if used to power an EV, would take the EV as far as the REST of the barrel takes our average oil-fired car. That doesn't include the cost of oil wars, oil diplomacy, patrolling oil supply lines, oil spills, oil exploration, oil transmission, the natural gas used in refining, the potable water (20 to 60 gallons for each barrel) used in the refining process...
    So when we hear these weak arguments about "EVs have a long extension cord reaching into the coal mine" it's difficult to retain a straight face and even disposition.
     
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  16. fb_1376616026 avatar Doug Korthof Posted: 5/13/2010 9:21am PDT

    The Prius battery, according to Priuschat and some Toyota execs I've spoken with, cycles from 40% to 80%, or about .5 kWh, about 3 miles all-electric range (if you go very slow). But it's easy to understand why other folks could cite other numbers: one authority says 50% to 80%, but a lot depends on the condition of the battery and the voltage.
    We are clear about one thing: the Toyota engineers who designed the Prius were not the same as those who designed the RAV4-EV. The approach of the former is bass-ackward; they looked at it as a gas car with a battery assist. The RAV4-EV uses the full power of its 30 kWh battery pack to go from 1.45 volts per cell down to 1.0 volts per cell, or lower, for a nominal "range" of 100% to 0%.
     
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  17. fb_100000458268753 avatar Neil Blanchard Posted: 5/13/2010 11:59am PDT

    Hi John,
    Between this news and the recent announcement from Toyota about a $50,000 hydrogen fuel cell extended range EV in 2015, I am thinking that Toyota is going to let others lead us into the age of EV's. Remember, this plug-in Prius may not be released in quantity until 2012, or later?
    As others have already mentioned: Toyota *please* give us a RAV4 EV along with a Matrix/Corolla EV (virtually the same drivetrain?) and an iQ EV, and a plug-in CH-FT with 80-100 miles of electric range!
    Sincerely, Neil
     
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  18. By  Efried Posted: 5/15/2010 1:57am PDT

    There are successful big OEMS, Me-Toos and plenty of start-ups. Toyota has learned how to use the halo effect from the Prius to sell V8 Landcruisers and Lexus fuel guzzlers but they will not invest into unsure ground. That's the reason why the PHEV design is half baken. But I bet once they have the same brilliant idea like the THSII they will present a sound PHEV or serial hybrid design. I guess they are just waiting for the markets reactions on the GM-Volt.
     
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