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HV Battery Pre-Heat... Anybody tried it?

Discussion in 'Gen II Prius Technical Discussion' started by Rokeby, Jan 25, 2009.

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  1. Rokeby

    Rokeby Member

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    HV Battery Pre-Heat; possibly an overlooked cold weather FE/MPG tweak.

    This thread is an attempt to give stand-alone visibility and direct access to
    an idea that was embedded in another more general thread. I'll begin by
    extracting, and editing for brevity where appropriate, the relevant posts.













    Ok, that's the introduction.

    Once again, has anybody tried something like this? If so, any pics? Any
    comments, suggestions, dire warnings are welcomed.

    As a preliminary concept, I'm thinking of something that would have maybe
    100-200 watts heating output, enough to get ~75 degF air, and a small muffin
    fan to move the air through the existing battery cooling ducting. It would be used
    along with a electric block heater EBH for two or three hours before start-up on
    cold mornings.

    I'm still hunting around for some pics/drawings of the HV battery and the
    associated ductwork, especially on the exhaust side. When I find something,
    I'll post it.

    Of course, if you have something ready-at-hand, your posting it is welcomed.
  2. statultra

    statultra uber-Senior Member

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    My 2001 Prius has a issue where the battery gets hot and the fan stays on almost all the time, ( i live in florida ) the gas mileage is pretty amazing to say the least, hopefully one day when I drive it ill post a video of my speed vs mpg
  3. Celtic Blue

    Celtic Blue New Member

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    From what I gathered in the recent regeneration discussion the best way to preheat it is probably to charge it--as in plug in charging. It would seem to be considerably more efficient than external heating.

    An ideal system would do this on some sort of timer. It would be nice to hit a switch and start a warm up sequence (perhaps running the car's electric heater and blower as well to warm the interior.) After ~5 minutes, disconnect the plug, start the car and drive off with warm interior and happy battery.
  4. Flying White Dutchman

    Flying White Dutchman Senior Member

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    yes
    this would be nice
  5. PaulHS

    PaulHS Member

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    Somewhere on PC is a thread (not found by search) where a guy had posted an arrangement (with pictures!) in which he placed a flat yellow heating pad of some sort on top of the battery pack. Don't know how he powered it. So it has been done and reported here.

    I had bought a small ceramic heater intending to install it between the grille and the radiator to provide additional heat to the engine. But since the weather is too cold to be tearing apart the front of the car, I've gone with a more low-tech setup. The electric heater sits on the floor on the front passenger side of the passenger compartment facing the driver's side. The power is adjusted to about 600 watts and the power cord is fed out the passenger door. Closing the door leaves the cord snug but not overly tight. I run an extension around to the grille where the EBH plug is located. Power is fed from the EBH timer to a double socket to the EBH and to the ceramic heater so that both turn on at the same time.

    The primary purpose here is to pre-warm the passenger compartment. This way the ICE does not need to provide heat for passenger comfort. This works surprisingly well. On 25 degree F days, on my 8-mile commute, the passenger compartment stays toasty without turning on the console heater at all.

    Secondly, the preheat will melt frost or light ice which may have accumulated on the windows overnight. And seriously, if this were the only benefit, it's well worth not having to scrape the windows.

    Thirdly, I believe that, as a bonus, the circulating heat provides some warmth for the HV battery, though I have taken no measurements yet. Efficiency? No idea. But it's great to step into a warm car in the morning!
  6. Flying White Dutchman

    Flying White Dutchman Senior Member

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    i think the energt lost in heating the pack is more then just keeping the charger cycling a charge to the battery pack!

    so maybe just charging it during the night and when its full let the charger connected do the moment it just drops a little bit the charger begins charging again!

    then the energy is not a total loss
  7. Celtic Blue

    Celtic Blue New Member

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    The key is that charging the pack should be part of the warm up sequence...prior to actually starting the car. Keeping it warm all the time makes little economic sense to me as it is wasting electrical power. But using the grid to warm the battery just before driving makes good sense.
  8. Rokeby

    Rokeby Member

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    Shawn Clark and Flying White Dutchman,

    Thanks for your posts. But, I have a sense that you guys are going off in a
    different direction with the charging and heating idea. Interesting, but not
    readily do-able on a garden variety Gen-I or Gen-II car.

    I'm hoping to get info/ideas on HV battery warming ideas that are doable on
    the cars and HV batteries that we have now.
  9. firepa63

    firepa63 Former Prius Owner

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    I hope the fire station is just around the corner...:rolleyes:
  10. PaulHS

    PaulHS Member

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    What exactly is your concern? Or is this just a smart alec remark?
  11. firepa63

    firepa63 Former Prius Owner

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    Placing a space heater inside a vehicle is a very dangerous practice. The inside of any vehicle is full of combustible material.

    (Retired Fire Fighter)
  12. David Beale

    David Beale Senior Member

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    I don't see the point to all this. If you just start the car it will have the battery warmed up in a few minutes as the system charges it. If you actually -drive- the car it will heat up the battery even faster.

    With the NiMH battery getting heat -into- it is not the concern. It's getting the heat -out- of it that's most important.

    I have parked Pearl in -30C temps for 5-6 hours and a low temp in the traction battery was NOT a problem. It was the low temp in the cabin that I was concerned about. ;) It took two to three times as long to warm up the coolant than normal so I could get heat.
  13. Guy in WNY

    Guy in WNY Junior Member

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    Hi,
    I've also used a space heater, the oil-filled type that look like an old fashoned radiator sort of, to keep my car warm in the winter. It's great to just brush the car off - no scraping - also, it's nice and toasty warm to get in and drive away. That was last winter. This winter, my wife and I cleaned out my half of the garage, I installed a new garage door opener, and just park inside now. No need to scrape. I think I'll toss the heater back in also, and see if my mileage gets better. I seem to remember it got a little bit better last year when I did this, by just a few tenths? Maybe?
    AND it's very safe. Modern day space heaters are so overloaded with safety features it's a wonder they even put out any heat!
    My 2 cents.
  14. dr_d12

    dr_d12 Member

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    In my experience, below about -25C the traction battery is useless - the car feels like dead-weight like it does when the battery charge is in the red and the car won't use the electric motor * .

    I don't believe the part of this thread about warm cabin air in the car heating the battery. Consider putting a piece of ice the size of the battery into the battery space, then heat the passenger compartment to 18C - how long would it take for the ice to melt?

    As was said, the car charges and discharges the battery to warm it up, then 5 or 10 minutes later everything is back to normal.

    Over at GreenHybrid there is a thread about adding a battery blanket to the traction battery:

    Battery Blanket - GreenHybrid - Hybrid Cars




    (* This happened to my car twice. The first time, the guys who tinted my windows figured out a way to discharge it while he had the car. The second time, the guys at the autobody figured out a way to discharge it. -Some lady in a truck ran into me while I was at a drive-through buying a milk shake.- Both happened in spite of me showing them to turn the car off after they got it in the bay.)
  15. David Beale

    David Beale Senior Member

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    Hmm, well Pearl drove normally after getting "cold soaked" to -30C. That is, started right up, pulled away as fast as was possible on the snow/ice you get in those temps. In fact, Pearl pulls away faster than -most- other vehicles, including 4X4s. Of course the Nokian WR tires have -something- to do with that traction wise. But I've never noticed a loss of power when she was cold. Stiff shocks, stiff tires, etc. yes. So I don't get rambunctious unless the pavement is nice and smooth. ;)
  16. JimboK

    JimboK One owner, low mileage

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    I would modify your first sentence to say the car tends not to use the electric motor in extremely cold conditions until the ICE reaches full operating temperature (70C/157F). But, as several of us discuss here, once this temperature is reached, normal S3/S4 operation, including "pedal-feathered" EV mode, is allowed.

    FWIW, I've seen this behavior with temps as high as mid-teens Fahrenheit (-10C or so). A key issue (though perhaps not the only one) is hybrid battery temperature -- hence the discussion here.

    I tend to agree that warming the cabin will warm the battery pretty slowly. Actually using the battery likely will warm it faster, but that's part of the problem: it won't allow itself to be used when the car is very cold. It will, on the other hand, tend to build a higher charge during cold weather warmup, which will help heat it. Then when S3/S4 temperatures are reached, it easily uses that charge which adds yet more heat.
  17. PaulHS

    PaulHS Member

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    I'm using a small ceramic heater. It has no exposed element or wire. And, of course, the fan circulating the air lowers the temp of the ceramic element. I have felt the surfaces closest to the heater after three hours of running and they were not even hot to the touch; perhaps comfortably warm. It's hard to imagine any way for something to ignite.
  18. Celtic Blue

    Celtic Blue New Member

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    Anything below 20 F and it takes ages before the car stops wanking with charging the battery.

    I'm not so sure that the car intentionally won't let us use the traction battery until it is warm. Instead I suspect that it effectively can't use the battery within the normal control scheme. It is going to have a very narrow available throttle band (compared to comfortable temperatures) at least at moderate throttle. Just running the blower, lights, and normal operating electronics is going to steal a considerable portion of what little output the battery has until it warms--even worse if the driver is wanting heat and the electric heater is running. I don't know if the controller says battery voltage is too low or what it uses to make its determination.

    The other thing I notice is that the battery tends to drop a bar or even two when it is really cold. If say I park with X bars (warm battery) it will restart with X-1 or X-2 after a cold soak. Indicated SOC doesn't seem to compensate fully for temperature (something I've been meaning to ask about.)

    All told I get a "chicken or the egg" feeling when I try to reason through this.
  19. Rokeby

    Rokeby Member

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    Thanks to all the posters who have provided comments.



    Yeah, when I think hard on this I end up going in circles too.

    If you set the cabin heat to say 70 degF to warm you and by extension the
    HV battery, you get a big MPG hit. If you intentionally end a day with low-ish
    SOC, say 4 bars, so that the HSD starts out the next day charging the
    battery to warm it up, you get a MPG hit. If you end the day with a high
    SOC, the HSD seems to avoid using the HV battery for propulsion assist until
    the coolant temps are up to 157 degF... guess what? a MPG hit.



    I've been poking around the 'net and found some interesting material.
    Unfortunately, none of it is conclusive. Still, I'm going to post the sites as it
    is possible it will help others considering this matter.

    Here is thread from 2006 featuring efusco discussing this very idea:

    PriusOnline.com • View topic - Electric Battery Blanket?

    What if any actual implementation was done is unclear.

    No matter how I look at it, I see the HV battery temps as the controlling
    factor. So how to work around it? Simple, pre-heat the battery. Simple to
    see, but not simple to address. Two possible approaches; keep the battery
    temps up while the car sits overnight, or preheat in the morning.

    Preheating the cabin would seem to be very inefficient if the intent is to
    warm the battery. There is nothing carrying the heat to the battery. To get
    that, you have to circulate the warmed air through the battery cooling
    ducting. And, if you do that with the stock OEM ducting, after one pass over
    the battery, the warmed air is exhausted outside the car.

    Warming the battery with heated air with any king of efficiency would
    require modding the HV battery ducting, intended for cooling the battery, to
    include recirculating the heated air. This arrangement would have to be
    reversible for hot weather operation when you want to dump the air used to
    cool the battery.

    Looking into heating the battery itself, there seems to be three possibilities:
    an electrically heated/insulated blanket, an electrically heated plate, and a
    engine coolant heated plate.

    http://www.zerostart.com/UserFiles/File/08 ZEROSTART GUTS US.pdf
    Kim Hotstart Battery Warmers
    Battery Warming

    The thread originally cited by dr_d12 has pictures of a battery blanket used
    to warm the HV battery case.

    Battery Blanket - GreenHybrid - Hybrid Cars

    The blanket is yellow, so this is probably close to the thread alluded to by
    PaulHS in post #5.

    Just how much this arrangement warms the battery inside the box is unclear
    as there is an air-gap between the case and the batteries.

    This matter of warming HEV and PHEV batteries has engaged the Matsushita
    company enough that they have taken out international patents on their
    answer:

    (WO/2003/001313) TEMPERATURE REGULATOR OF STORAGE BATTERY AND VEHICLE INCLUDING THE SAME
    (WO/2003/001313) TEMPERATURE REGULATOR OF STORAGE BATTERY AND VEHICLE INCLUDING THE SAME

    So, for now, I'm still going around in circles...
  20. JimboK

    JimboK One owner, low mileage

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    Another observation that relates to this thread:

    I was out of town on business last week (in "Merlin" in fact). The car sat for several days in the parking lot before I headed home, so it had a good cold-soak. I hit the road Friday morning, straight onto the highway, with HV battery temperature at 32F. I had a passenger, so I ran the cabin heat. She had a coat on and I had an insulated vest on, so I didn't have to run it too hard to keep us comfortable -- thermostat temps in the low 70s. That's still considerably warmer than I normally keep it. After about 20-30 minutes on the road the HV battery temperature was still 32F.

    This demonstrates how ineffective a warm cabin is in warming the battery. I really didn't see any appreciable warming until a little later in the drive when I had the opportunity for regeneration and lower-speed pedal-feathered EV mode.
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