HV Battery temperature control

Discussion in 'Prime Technical Discussion' started by ronw, Jan 30, 2018.

  1. ronw

    ronw Junior Member

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    Some interesting photos of cutaway models of the Prius Prime battery on the hybridlife website under the title "Toyota Prius 4 rechargeable: les derniers details devoiles au".

    It appears from these photos that cell cooling/heating is achieved by drawing air from the cabin, up between the cells and out through two centrifugal fans exhausting to the outside through the rear floor pan. Moreover it seems that the battery case has built-in channels (making it almost double-walled) through which some of this air can also be directed. This is presumably to help heat-up or cool-down and perhaps also to avoid condensation inside the battery case when warm humid cabin air is drawn through a cold case.

    Below each of 5 banks of cells there are two resistive strip heaters, one of which Toyota has labelled "battery heater" and the other "battery warming system".

    From the owners manual, battery cooling is apparently achieved by cooling the air using the cabin air conditioning system. The owners manual also indicates that a "battery heater" will keep the battery at around 32F while plugged in (presumably to avoid charging at lower temperatures, which is not good for lithium ion cells). After 3 days in this mode however, the manual says the car will exit this mode and stop heating the cells (presumably to save energy, since I believe the battery heater draws around 1.4kW).

    If, however you have a Canadian or Alaskan car, another system will kick-in (as per owners manual) following the 3-day trip. That system applies for 31 days and will until then start the charging process as soon as the car is plugged in (over-riding any call for delayed charging). It will also apply "battery warming" (as opposed to "battery heating").

    So it seems that for Canadian & Alaskan cars there is a special heating mode for cars that are not used regularly (i.e., left more than 3 days on the charger without unplugging). Prior to the mode switchover the design philosophy is to keep the battery above 32F until the pre-programmed charge time. But after switchover the car will start charging as soon as it is plugged in (when presumably it is still warm from use), and then keep it "warm" (which may mean at a lower temperature than 32F) until it is driven. This would be entirely reasonable since using a lithium ion battery at temperatures much lower than 32F is not a problem, but charging one at low temperatures can result in permanent damage.

    There is one other thing that the owners manual says happens when the car does this mode switch-over... the battery somehow "insulates" itself. Here is how it is worded:
    Hybrid battery (traction battery) warming control (Alaska and
    Canada only) This control operates after the charging cable remains connected to
    the vehicle for 3 days and “Traction Battery Heater” automatically
    stops. It automatically insulates the hybrid battery (traction battery)
    in extremely low temperatures.

    Could they mean "isolates" instead of "insulates"?...Perhaps the inlet and outlet air ducts close to try to conserve heat?

    I would appreciate any comment or thought that others have on any of this, as I live in a pretty cold part of Canada and want to understand the inner workings of the Prime's system so I can best adapt my charging routines to it.

    On a related note:
    For those of us living where winter temperatures are often below the 14F threshold for effective heat pump warming of the cabin, it would sure be nice if the Prime would allow us to remotely start the engine without having to go outside to unplug the vehicle. The Volt allows this, but for some reason the Prime disables both the gearshift and the ICE start-up when the charge cable is plugged in.
     
  2. Elektroingenieur

    Elektroingenieur Senior Member

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    There is a bit more information about HV battery cooling and heating in Toyota’s New Car Features book, available by subscription to techinfo.toyota.com, including diagrams of the cooling air flow and an illustration of the heaters. The cooling air “is discharged under the deck board,” which I think means to the vehicle interior, and there is only one set of resistance heaters for the battery, one per battery stack.

    The explanation in New Car Features, in the Plug-In Charge Control section, about what happens after 3 days in the Frozen North (※) isn’t much clearer than the one in the Owner’s Manual:

    (4) When "HV Battery Heater" automatically stops after the charging cable remains connected to the vehicle for 3 days. It automatically increases the temperature of the HV battery to warm the HV battery in extremely low temperatures. (Alaska and Canada Only)​

    The part of the Owner’s Manual that you quoted doesn’t appear in the Japanese or European editions, but it is in Toyota Canada’s French-language edition of the Manuel du Propriétaire (74,1 Mo PDF):

    ■ Commande de réchauffement de la batterie hybride (batterie de traction) (Alaska et Canada uniquement)

    Cette commande fonctionne après que le câble de charge est resté branché au véhicule pendant 3 jours et “Réchauff. batt. traction” s’arrête automatiquement. Elle isole automatiquement la batterie hybride (batterie de traction) sous des températures extrêmement basses.

    ● Cette commande s’arrête 31 jours après le branchement du câble de charge, même s’il est encore branché au véhicule.

    ● Lorsque cette commande est en fonction, les paramètres de la minuterie de charge sont ignorés et la charge débute immédiatement.
    Here isole would seem to be electrical isolation, unless the authors are speaking figuratively of isolating the battery from the effects of cold by heating it. At any rate, I’m not aware of any dampers or the like, not that these would be effective on a cold-soaked car.

    I assume you already noticed the cold temperature limits in the Owner’s Manual (pages 92 and 146):

    ■ Starting the hybrid system in an extremely cold environment

    When the hybrid battery (traction battery) is extremely cold (below approximately -22°F [-30°C]) under the influence of the outside temperature, it may not be possible to start the hybrid system. In this case, try to start the hybrid system again after the temperature of the hybrid battery increases due to the outside temperature increase etc.​

    ■ Usable temperature range

    ● Do not charge if the outside temperature is -22°F (-30°C) or below, as it is likely that charging will take longer, and equipment related to charging will be damaged.

    ● Do not leave the vehicle or the charging cable in areas where the outside temperature is lower than -40°F (-40°C). The vehicle or charging cable will probably be damaged.​

    (※) Here in California—tomorrow’s forecast high, 80 °F (27 °C)—just thinking about these temperatures makes me chilly.
     
  3. ronw

    ronw Junior Member

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    Thanks Elektroingenieur for the further insights.
    The battery is pretty easy to get at, so when I get my Prime (dealer here in Ontario, Canada tells me early March) I will figure out how the battery heating system works on a Canadian car and report back.
    I haven't been able to access any info through Toyota's techinfo site (paid $15 for a 2 day subscription but couldn't find a way to open it with my Mac), other than to look at the list of manuals/literature available there for the Prime.
    It would seem that full service documentation (like the 5 or 6 manuals I have for my 2005 Prius) is not yet available. Is that true?
    In your opinion does the TIS system currently have enough worthwhile tech info on the Prime to warrant me buying a cheap ebay PC as well as paying for a month TIS subscription?
     
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  4. Elektroingenieur

    Elektroingenieur Senior Member

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    The Repair Manual, Collision Repair Manual, New Car Features, and Electrical Wiring Diagram for the Prius Prime have been available to TIS subscribers since mid-2017. The latest editions cover 2017 and 2018 models. The site also has the 2017 Toyota New Technology Update training course (see the outline I posted), plus many others, assorted bulletins, and repair time estimates from the Flat Rate Manual.
    There is a good deal of useful information, but keep in mind the intended audience and the limits of what Toyota discloses in their publications, as I discussed in a previous posting.

    I’m not sure why TIS wouldn’t work with your Mac, especially if you were able to register and pay, which was broken until recently for browsers other than Microsoft Internet Explorer, but has now been fixed. I’ve used the site, including the EWD Viewer, successfully with the Safari browser. It does use pop-up windows, though.
     
  5. Gaëtan Lafrance

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    You're right for the translation from french:''Elle isole automatiquement la batterie hybride'' means effectively electrical isolation from th electrical system.

    Bonne journée.
     
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