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Battery vent fan

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by romad, Aug 9, 2009.

  1. romad

    romad 2004 Prīus Base Former Owner (Sold 13 May 22)

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    I just returned from a two week vacation and had an incident that I haven't seen before in the 5 years we've owned the car.

    Last Thursday we were driving the rim of Crater Lake, Oregon and all of a sudden a loud fan sound started coming from the rear that I deduced was the battery vent fan. I immediately checked the battery charge and it had 4 blue bars. After several minutes, the fan quit.

    About 2 hours later as we were leaving, actually "gliding" down the road, the fan started again; the charge indicator was 2 bars short of a maximum charge having about 8 green bars. This was after the car had been parked for 60 - 90 minutes while we had lunch. Again after several minutes the fan stopped and hasn't reoccurred. Both times the outside temperature was about 48 degrees Fahrenheit/9 Celsius.

    Should I take the car in to the dealer and have it checked? Does this mean I need a new battery? I had the 60,000 mile service done July 24th just before we left on vacation, but we put about 2,000 miles on during the trip.
     
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Did you check to see that the rear seat Battery air intake vent was unobstructed? It is on the upper passenger side.
     
  3. krousdb

    krousdb NX-74205

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    The very same thing happened to me in my first year of ownership. It has never happened since. I can't explain why it happened. I haven't thought of it until just now when you mentioned it.
     
  4. lenjack

    lenjack Active Member

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    Battery vent fan is for the small 12 volt battery in the hatch over the right rear wheel. The number of bars you see as nothing to do with the rear batery, and monitors only the front, traction battery.
     
  5. krousdb

    krousdb NX-74205

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    Um, the 12V battery doesn't have a vent fan, nor does it need one. It has a vent tube. The battery vent fan is for the traction battery so the number of bars IS relevant. The intake is near the passenger side rear seat, the exhaust is through the vent in the passenger rear quarter panel, which happens to be near the 12V battery.
     
  6. romad

    romad 2004 Prīus Base Former Owner (Sold 13 May 22)

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    Yes, it was clear.
     
  7. romad

    romad 2004 Prīus Base Former Owner (Sold 13 May 22)

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    Don't know about the Classic model but in the 2004 and later models, the traction battery is in the rear UNDER the rear seat area and it has a vent fan. The vent intake is on the upper right of the rear seat. The bars shown on the MFD display the charge of the traction battery. The small 12 vdc fan-less battery is in a well behind the right rear wheel.
     
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  8. qbee42

    qbee42 My other car is a boat

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    This comment is in error. The battery vent fan cools the HV traction battery, not the small 12 volt battery.

    Tom
     
  9. CBarr31

    CBarr31 Active Member

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    I can't find the old thread on here to post the information but I am pretty sure there are 3 thermistors that control the battery vent fan.

    I remember reading that somewhere and think it was Patrick Wong (Prius Expert, IMHO) that made the statement. There weren't any temperatures listed for the cut in/cut out of the fan however.

    Hope this helps. Happy driving.

    Chris
     
  10. Rae Vynn

    Rae Vynn Artist In Residence

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    The vent fan function is determined by temperature, not by SOC.

    In other words, the number of battery bars is completely irrelevant - the temperature of the battery is the deciding factor.

    You might vacuum out the fan area next time you clean your car, to reduce the noise from dust build up. Make sure the seatbelt doesn't cover the fan grill, etc.
     
  11. jayman

    jayman Senior Member

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    Correct. Here is a photo - I didn't take it - of the fan ductwork

    [​IMG]

    Now that I think of it, I don't recall the vent fan ever running in my 2004 Prius
     
  12. romad

    romad 2004 Prīus Base Former Owner (Sold 13 May 22)

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    That is what I find perplexing: the fan NEVER comes on during our triple-digit summer temperatures, nor does it in the below 40 degree Fahrenheit winter temps. Yet it came on in 48 - 50 degree temps at Crater Lake. Perhaps the altitude/elevation had something to do with it? The air pressure is lower at that height, and this was the first time we were at that height for an extended period.

    How do I get to the fan area to vacuum it out? Remove the rear seat?

    And as I said previously, the vent grill was and is UNOBSTRUCTED.

    Meanwhile, no one has answered my main question: should I take it to the dealer, or just wait to see if it happens again?
     
  13. jayman

    jayman Senior Member

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    The elevation and sudden charge/discharge cycles probably had a lot to do with the fan operation

    As you can see from the photo, you have to remove quite a bit of trim to get to the duct. I would not recommend trying to take the cover off the NiMH battery pack, unless you are aware of and comfortable with the voltages in there

    I suppose if you have dogs/cats riding in the car all the time, every 2-3 years you will have to vacuum out the duct and battery
     
  14. romad

    romad 2004 Prīus Base Former Owner (Sold 13 May 22)

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    Well then, I guess that the ambient air PRESSURE is a factor in the vent fan control since the fan has never come on in higher/lower temps with the same charge/discharge cycles. I'm not going to take it in to the dealer in that case.

    I wonder what would happen if I blew air INTO the exhaust port? Would it blow dust out the vent intake by the seat? I'll have the right rear door open if I do that!

    Nope, no animals at all.
     
  15. Rae Vynn

    Rae Vynn Artist In Residence

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    I meant just run the vacuum hose over the surface of the fan vent when you are doing the car.

    The fan comes on when the battery needs it to. Most of the time, the battery is kept comfortable by the ambient cabin temperature. If you are driving at higher speeds, the fan may come on and then go off again without you ever noticing it. Since you were gliding, there wasn't enough exterior road noise to cover the sound.

    You mentioned that the car had been sitting for over an hour before you heard the fan. It may have just gotten warm enough in the battery area for the fan to need to start up. This is not an issue that needs to be taken to the dealer -- the fan is there for just this reason.
     
  16. romad

    romad 2004 Prīus Base Former Owner (Sold 13 May 22)

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    That was the second time. It had been sitting in the parking lot, ambient air temp in the mid/upper 40s FAHRENHEIT except when it was not raining, then the Wind Chill was in the lower 40s. It was cold; glad we didn't take the 2 hour open-boat tour!
     
  17. donee

    donee New Member

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    Hi Romad,

    The amount of cooling a flowing fluid can provide is dependant on the mass flow. High altitude air weighs less. Humid air weighs less. The fan can only push so much volume of air through per unit time, and if that volume has less mass, it cools less. This is a similar problem to aircraft taking off from high altitude airports having less weight lifting capacity - as the air being thrown down off the wing weighs less. Shut windows damps down the air flow some too.

    Now, the battery has allot of mass, and if it was just in a desert, and driven up a mountain into thin air it was heavily exercised, and then put a low cooling situation. Not allot of heat can conduct out of the case, rapidly. It takes half a day for that.

    Did you have the cabin heater set at 80 maybe ? In which case the air flowing into the battery is hot, beside being low density.
     
  18. northwichita

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    I think it should be noted the multiple fan settings........Quote
    The fan has four settings, depending on the maximum temperature of four monitored (sites within the) batteries. Toyota also monitors the inlet and outlet air temperatures. The fan settings are off, low, medium, and high speed. The blower setting depended on temperature and transitions with hysteresis depending on whether temperature is increasing or decreasing. unquote

    from Toyota Prius Hybrid Battery Pack Information
    which has a lot more detailed information about battery temperature control.
     
  19. jayman

    jayman Senior Member

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    If you do mountain driving, eg steep grades, that will put a lot of stress on the battery pack. Climbing a steep grade, will deplete the battery pack, warming it up.

    When you descend that steep grade, there will be a lot of regenerative braking. That will also heat up the battery pack
     
  20. yardman 49

    yardman 49 Active Member

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    As Northwichita pointed out, the traction battery fan has multiple speeds.

    Because of this, some owners don't realize that there are many times that the fan is running at "low" speed, but because they can't hear it, they assume it is "off".

    Then the first time it runs on high, they finally hear it and think that something is wrong.
     
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