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Traction battery fan

Discussion in 'Gen III 2010+ Prius Technical Discussion' started by yeldogt, Mar 23, 2012.

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  1. yeldogt

    yeldogt Member

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    Was driving the Prius yesterday -- Temps got up to 70 and I heard the fan located at the right of the back seat for the first time .... not the quietest thing on the planet!

    I tried doing a search with limited results -- can anyone direct me to some threads that explain the operation.

    The fan was most prevalent when I was driving at about 35mph - I was surprised how loud it was. Is the vent I see an intake?
  2. jdcollins5

    jdcollins5 Senior Member

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    The battery fan has six speeds and runs based on a battery temperature sensor. You are correct that it can get loud when it gets up to the top speeds.

    The vent by the rear passenger seat is the air vent for the HV batteries. The blower motor pulls cabin air through this vent and discharges externally. A good reason to keep your AC running in the summer to keep your batteries cool.

    At 35 mph you were probably running on the batteries with the ICE off a lot thus causing the batteries to heat up.
  3. jdenenberg

    jdenenberg EE Professor

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    Please check the HV battery fan vent for lint as a clogged vent will cause the battery to overheat and shorten its life.

    JeffD
  4. seilerts

    seilerts Battery Curmudgeon

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    That's very unusual for a car that new, and temperatures that mild.
  5. yeldogt

    yeldogt Member

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    This car was purchased in January - has about 2500 miles on it.

    It was sunny yesterday -- about 70 degrees - two people in the car with the AC on.

    I have no reference point -- this is the first I have heard the fan.

    It was the sound of a rush of air -- not a mechanical sound of a fan hitting the shroud or a bearing failing.
  6. jdcollins5

    jdcollins5 Senior Member

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    Any chance you were doing a lot of short trips with stops in between? That is when I normally see the battery fan run. The battery temps get up while driving a lot in EV and then the battery temperature continues to rise while stopped.
  7. yeldogt

    yeldogt Member

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    I was driving along mixed traffic for about one hour.
  8. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Are you sure there wasn't anyone sitting in the back seat who could have been blocking the HV battery vent? If there was and even if they swear they weren't blocking the vent, they probably were.

    If nobody was on the back seat and nothing was blocking the vent, then are you 100% sure you haven't been leaving the a/c on full recirc?

    I have only ever had the rear vent fan blow so loudly that I could hear it in 65,000 hard taxi miles. Our max temps over here are about 29/30c (mid 80's.) and I worked the car hard for 10 hours a day.

    The HV battery fan sounds like an old fashioned hair dryer.
  9. yeldogt

    yeldogt Member

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    Just drove it to an appointment -- about 20 min both ways. I could hear the fan every time the car was going about 35-40 mph ... it would go off as I slowed down.

    AC on "auto" -- it is in the 70's today
  10. andyprius

    andyprius Senior Member

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    Since you bought the car used you know little about its condition. You can check under the trunk and remove the air duct and see if your getting a good flow of air and not too warm ( around ambient or human comfort zone) The previous owner could have had a big shaggy dog that constantly lost fur and the vent is clogged! Always run the car temp at your comfort zone, windows or AC, it does not matter. When you are happy so is the HV Battery. :cheer2: The inverter temp should also be monitored, altho I have always found it cool to the touch.
  11. GrumpyCabbie

    GrumpyCabbie Senior Member

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    If the fan is running high even now and the vent isn't blocked, I'd be inclined to get it checked out by a Toyota dealer/agent. If it's a 2011 it should be under warranty and if there is a fault, it's better to find it sooner than later.

    Just to clarify one point; despite having the a/c on auto, do you have it set to recirc all the time? If so try adjusting it to allow outside air in and see if that solves the issue.
    1 person likes this.
  12. friendly_jacek

    friendly_jacek Senior Member

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    if it stops when one stops driving, its a wind noise. sometimes I hear it and it sounds a little like fan and from that direction too. Once my rear passanger told me it sounds like the rear right door is not closed completely. I think the air duct transmits wind/road noise.

    I had high speed fan only once, after my wife driving. The fan was on all the time and hybrid battery was not functioning with poor MPG. Clearly overheated.
  13. andyprius

    andyprius Senior Member

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    The cooling air eventuallly exits on the right and left side of where rear fenders might be on a earlier auto. These are louvre type doors, very sensitive. Possibly some air is flowing outside these louvres causing them to open a bit, this would cause air or wind noise back thru the air intake at the back seat. If the Prius is still in warranty let them check it out. If no longer in warranty, buy a pair of ear muffs. :cheer2: Seriously, if you really think it is overheating, you must have it looked at. Extended high temperatures will kill the HV Battery!
  14. friendly_jacek

    friendly_jacek Senior Member

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    Like I said, it happened only once when my wife turned the car off after some excessive brake use in a hilly terrain and parked in a sunny spot on a hot day. I only discovered it when I turned it on sometime later. The fan was going like crazy and there was no battery assist whatsoever. I know heat kills HV, but not every driver is going to be tuned to the HV health all the time and the design error (shutting the HV fan off with ignition off) doesn't help either.
  15. ImeanGreen

    ImeanGreen Prius v Five BP Brigade #236

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    I heard mine the first time a couple days ago when outside temp was over 80 degrees. I think that when the car is exposed to heat for a good amount of time while being parked, the vent fan starts to kick in for a few miles when you first drove it and stops when the inside temp gets cool enough. BTW, this was before I got my heatshield. Since having the heatshield, never heard the vent fan again. Car tinted 25% all around except windshield.

    Friendly_jacek, have your car tinted if you haven't done so and you may need to buy a heastshield. Heatshield may be bulky but it's worth it.
  16. jdcollins5

    jdcollins5 Senior Member

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    I have been monitoring my battery fan with ScanGaugeII since the weather has warmed up. The part about the battery being exposed to heat when parked in open parking lots is correct. Since the weather has warmed up to the low 80's, I have seen the cabin temp and the battery temps in the 90's in the afternoon after sitting in the work parking lot. I have not started using a windshield heat shield yet.

    The battery fan does not come on until the battery temps get close to 100F. I have a 26 mile commute with mostly highway driving. The battery temp will begin to drop a little when I first start moving and the cabin temp cools down along with the battery fan blower temps.

    The battery fan does not come on until I get in to town with stop and go traffic. It will start out at Mode 1 right at 100F and will step up to Mode 2 and then Mode 3 as the battery temp rises to about 105 to 110F.

    So far I have not seen it above Mode 3 except when I forced it all of the way up to Mode 6. I cannot tell the difference between the cabin blower motor and the battery blower motor up to the Mode 3, unless I turn off the cabin blower motor. When it gets up to Mode 5 and 6 it is really screaming then.

    The battery temp is still above 105F when I park and the battery blower is still at Mode 3. The battery temp will continue to rise for a period of time after power is off before beginning to fall. I have wondered, like others, why the battery fan does not continue to run for a period of time after powering off.
    walter Lee likes this.
  17. ImeanGreen

    ImeanGreen Prius v Five BP Brigade #236

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    BTW, I always follow the facing west method with the heatshield when not under the shade. Works really well.
  18. GreenJuice

    GreenJuice Junior Member

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    I understand there are four battery temperature sensors. Do you monitor then all or choose between them? How did you decide?
  19. V8Cobrakid

    V8Cobrakid Green Handyman

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    i cleaned out hybrid battery fan, for the first time, 6 or so months ago.

    i've driven in a lot of different climates. sometimes the windows are up and sometimes they are down (definitely not a "windows up all the time" type of guy. i keep to the; windows up over 45 and open under 45. (for the last 2 years i've been in los angeles and it's usually windows up or slightly open. point being... if you keep your windows open, have animals, a lot of passengers, or smoke... you'll want to clean your fan blades. the vent usually doesn't show much. when i cleaned mine dust was caked up on the fan blades. i assume there really wasn't air flow or at least minimal at that time. my lesson learned is to clean the fan blades once a year. there is no such thing as too healthy of a fan

    another problem i noticed in the past. if you have a high state of charge on the hybrid pack or drain the state of charge before parking, don't turn off the car right away. let the idle cycle finish. i've noticed more of a problem with higher state of charge. When i returned to a full battery, it was much lower. i assume that the hotter battery is giving a false voltage. when it air cooled, the voltage dropped. when i returned to a drained battery (same SOC until the ICE startup process), the car flips out and runs high rpms to charge it (idle cycle while in P). i'm not saying the later is bad behavior of the system, simply annoying. (btw, low state of charge was an EV mode test.

    This may not apply to you. (rare cases... at least a lot more mileage than yours)
    the only other time i've ever read about a fan turning on high, was because of a hybrid battery failure. if you say it's rather loud, then that matches up with the whole "hybrid battery fan turning on high when the car notices a problem with the hybrid battery" topic (i'm sure someone else who reads this has the links for you). If it does happen to apply, it's under warranty.

    :focus:
  20. jdcollins5

    jdcollins5 Senior Member

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    There are actually three battery temperature sensors 1,2 and 3 and one battery blower fan inlet air temperature sensor. I have found that the middle temp sensor 2 is always the higher of the three so I monitor this one. I am not sure if the battery fan operates on the highest sensor or an average.

    When I am monitoring the battery fan speed mode I like to watch the middle temp sensor and the battery fan air temp sensor.

    After getting home from work tonight the fan speed mode was on 3. My wife and I went right back out for dinner. After dinner and starting home the fan speed was up to mode 4. When we got home I turned off the cabin fan and asked my wife if she could hear the fan and she could not. I asked her to listen next to the rear vent and she had to put her ear right in front of the vent before she could hear the fan.
    walter Lee likes this.
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