Battery vent fan

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

 

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.

 

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.

 

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.

 

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

Tom

 

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

 

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.

 

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



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

 

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

 

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.

 

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.

 

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.

 

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

 

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.