battery cooling fan mod

might be a good idea in warmer climates, driving with a/c on and fan running might extend battery life.

 

The most important thing is to check the fan and make sure it's clean. There's no filter to keep gunk out.

 

What makes you think that the designers of variable speed fan controls do a poor job optimizing? Is there some secret that you are not sharing with the rest of the engineering world?

Tom

 

Typically, they're optimizing for low noise, because when in the presence of a whiny fan, some of the whine is transmitted to people, which greatly amplify the whining.

There are a lot of problems that variable speed fans can have; for example, alternating between two speeds causing many thermal cycles when generating too much heat to stay in the lower speed, and too little to stay in the higher speed. This causes repeated mechanical stress as parts expand and contract, and can eventually cause failure.

That said, I'm not entirely sure what the triggers are for the fan in the Prius. Watching one of the battery temperature sensors once, the temperature was staying steady; not a degree up or down. The fan had gone to a relatively high speed, and then back down, without the temperature changing much. It may be that they've characterized the heat production of the battery at various SoCs and currents, and then preemptively cool it when you're, for example, charging many amps at high SoC. Or it may be that they're using a different temperature sensor than the one I'm looking at, which is closer to where the heat is being produced, and/or attached to a smaller mass.

In general though, I think it's probably a pretty well-designed system - I've heard that it's actually running quite a bit more than you'd think, it's just so quiet through about the first 6 fan speeds that you can't tell it's running without a gauge of some sort.

 

How do you get access to the fan, does the cover come off?

 

you cans earch for a thread with pics that explains everything.

 

The fan is optimized to run at the most efficient speed depending on the HV Battery temperatures. If you really want to manually control the fan speed, you can do it easily without cutting any wires:

1) Techstream with J2534 interface
2) ScangaugeII with Xgauge
3) Torque with ELM327 ( BT or USB )

Vincent

 

Exactly. There is a balance between noise and cooling, otherwise most systems would use single speed fans. Of course with big fans there is also an energy issue that comes into play.

The Prius is optimized to protect the HV battery. There is no reason to believe that the fan needs to run at a faster setting. Dog hair, on the other hand, can be a problem.

As for what triggers the battery fan in a Prius: it's the battery temperature.

Tom

 

I have noticed that auto AC in my high desert climate often turns to recirc. I have taken to setting the AC with manual non-recirc mode on the premise more cooled ventilation will reach the HV battery.

Make sense ? When I finally get around to installing the app torque, I'll monitor HV battery temps in both AC modes to actually see what differences are present. I've become a big fan [sic] of mothering the HV battery temps.

 

Here are some data recorded from my gen 2 Prius (US model 2009):







It looks like the HV battery cooling fan starts to turn on when the HV battery temperature is around 35C. During a record high temperature trip (under my climate and driving conditions) the HV battery temperature was kept under 45C with less than 10 V on the HV battery cooling fan (the fan was not maxed out yet).

Also see this thread:
http://priuschat.com/forums/gen-ii-...08-hv-battery-fan-voltage-vs-temperature.html

 

I have been monitoring my battery fan and temperatures for a while now, especially now that temps in NC have begun to get in the 80's. I posted some results under the thread 2010 Scan Gauge Work.

What I have seen agrees with 2009Prius but I monitor the battery fan mode rather than voltage. There are 6 modes which are set speeds.

The system appears to be smarter than just based on battery temperature. It also seems to set speeds based on OAT and whether the AC is on or off.

It appears that the basic is beginning at 95F (35C) that it increases fan mode or speed for each 5F increase. But I have seen the battery fan mode at 4 with as little as 105F and have also seen a battery fan mode of 1 at 114F on a cool day.

The battery temps here range from 90F in the mornings and up to about 110F depending on how much start/stop driving I do versus highway driving.

I have noticed that the battery temps rise quickly and drop very slowly. At nights when I park the car the temps are usually in the 110F range and overnight they only drop to about 90F even with the OAT in the 60's.

Even at a mode of 4 neither my wife nor I can hear the fan running unless we put our ear right up to the rear vent.

 

my 08 did the same thing with recirc. i always ran manual, temp low and a/c either on or off. if a/c off i'd want fresh air. if a/c on, i'd want cooled (recirc) air. but the manual always says to shut off recirc after the car cools down. some mfgs. call it max a/c . maybe it's so you don't keep breathing the same air?

 

I have not watched recirc versus non-recirc that closely, but one thing that I did notice that surprised me was that the cooling with convection only (battery fan not running) was not that good. The battery air flow temp would only be about 2-3 degrees below battery temps, regardless of cabin temp. Once the fan came on in just Mode 1 the battery air flow temp would drop almost immediately to about 2-3 degrees above cabin temp.

Depending on outside temps and cabin temps with just vent airflow the battery temps would stay fairly constant or at least not increase very much. With the AC on the battery temps would eventually begin to decrease. Of course this all depends on how much start/start driving you are doing during this time.

I will have to start watching recirc versus non-recirc to see if I notice any appreciable differences.

 

As you say, you're cooler with recirc on, which is better for the HV battery in hot climates. With the Gen 3, you won't be breathing the same air though as the Gen 3 Prius allows some fresh air in with recirc on. IIRC, the only time it shuts off the outside air altogether is when you press the "Pollen removal mode" button.

 

This is also the default mode for the Gen II. The Gen II always allows some outside air, even in recirc. If desired, the dealer can override this with a Techstream tool.

Tom

 

When taking apart the hv battery and accompanying ductwork, we find there are three thermistors attached to various parts of the battery pack and a sensor of some sort in the outflow duct leaving the pack (at higher temp) on the way to outside the car. This sensor has ribbed heat sinks on it and is near the R rear passenger side. This sensor is heated electrically and also has the warm outflow air from the battery blowing over it. Anyone know what that is and why it's heated? It gets almost too hot to touch if air is not flowing over it and cooling it and I've examined them on multiple cars and it is working properly. Thanks!

 

Probably an airflow sensor; heating it allows the determination of how fast air is moving past the heatsink. Without heating, all you'd know is the temperature of the outgoing air.

 

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