Traction Battery Temperatures

I bought a 2010 prius with 99k miles and the battery was dead too. About 2/3 of the modules were bad. I think its because it wasn't driven much and so left in the hot sun most of its life. Here is mostly low 80s all year. Just like ICE cars like to be driven so do hybrids. I'm super close to pulling the trigger on the lithium project Nexcell pack. One owner told me he's getting 70mpg on his 2014. Of course, $2400 is hard to justify but at $5/gallon it helps.

 

I have a 2019 pp advanced and recently moved to AZ where its much hotter during the summer. The car will spend a-lot of time outside during work. I have the OBDlink app and bluetooth tool with the prime PIDs and a dashboard setup for just the battery section. I have been very curious what the prime will do management wise when hot out.

My setup can observe the following parameters:

• 15 battery temperatures, 5 for each 19 cell pack.
• Cooling fan left/right intake temperature.
• Cooling fan left/right command speed 0-100%.

Overall conclusions:

• The battery temperature after sitting out most of the day is usually the temperature of the ambient. This correlation somewhat drops off as it gets really hot and I have never seen the temperature reach >110F. The car interior can get pretty hot but I also have expensive tint and a custom cut highly reflective sunshade always in.
• I believe the thermal management system has two primary modes. 1) The first mode is for speeds greater than 45 miles per hour. At this speed, when any sensor is measuring greater than ~95-100 deg it will kick on a temperature control loop to cool the battery down. On my car it seems to click off once the sensors all hit low 90s. The speed of the fans seem to correlate with cars speed, acceleration, and AC settings. Generally both fans are used here. 2) The second mode is for speeds less than 45mph. Within this mode it seems clear that it tries to push the max measured temperature to 105 or less. Generally the fan associated with the "hot" sensor is used. Anything below 105 the fans will not do anything until you pass 45mph.
• I can't hear the fans, even when I know they are on and I put my ear next to the intakes. But I know they are running because the cooling fan intake temperature drops immediately upon the command being sent. I can also feel the air flowing by.
• Air conditioning settings do make a difference but not substantially if you are comfortable. The biggest difference was observed running air to the rear under the seats. I tested this while the GF was driving and it seems to immediately lead to higher cooling fan intake temperatures. How that impacts the performances is hard to say. Running the AC at a higher temperature or lower fan setting with the air blowing 100% out the main vents barely moves the cooling fan intake temperatures, so I am going to assume that if you are degrading the cooling performance of the battery you are suffering in the car.
• Battery temperatures climb aggressively if you are hitting the battery hard in EV mode. Above "50%" power on the display you are pushing >50 amps and in doing so the battery temp climbs quickly. If you have this vehicle operating in hot temperatures I recommend keeping the amperage under 40 during the summer. It's slow, but the battery temperatures won't climb significantly.
• HV mode, especially on the highway, is really easy on the battery temperature. I suspect it's because the battery is so "big" relative to the normal Prius pack. Usually the car pulls 15-30amps max and puts the remainder of the demand on the ICE. As such, the temps drop substantially versus EV mode. This is to be expected in my opinion and below 95F ambient I don't think it make a difference. But when it is really hot out, consider just using HV mode.
• I haven't tested much when charging. If I "charge now" and its hot I do select the "can the car use AC while charging" option and it does turn the AC on full power. There is a 5 min delay before it becomes active. However, I generally only charge in the morning when <90F and the car has sat idle.

Hope someone finds this useful!

 

Thanks for the report. Very useful, although most of the results seem to be what is expected. One question. What is the App you used? I am assuming it is just an app, so all the temperature sensors you are monitoring are OEM sensors built-in to the car? Oh, and one more question. Can your set up a monitor battery temperature while the car is OFF? I live in a cold climate, so the high battery temperature is not something I am concerned about, but I am more curious as to how cold they get while the car is parked outside overnight.

FYI, I put Bluetooth temperature probes, one under the rear deck on the outside of the battery casing, another one in the center console between the front seat, and the third one outside of the car for ambient temperature. Interestingly, comparing three monitors 24/7, the temp probe on the casing of the traction battery is much better insulated than the cabin temperature measured inside of the center console. There is less temperature swing compared to the inside cabin or outside ambient temperature.

Just one question on this. Are you saying that directing the A/C to the rear increased the cooling fan intake temperature? Or is it a typo? It seems counterintuitive.

 

Yup, I am using the OBDLink app which comes with the OBDLink MX+. It’s pricey but works very well and has all the Prius PIDs. I also am not sure if the data is valid when the car is off. It does stay connected if I don’t remove it but the data looks like it freezes.

As for the second question. Yes as written was my observation. I have read of others putting the AC to mixed forward/feet so the battery gets more “direct air” from the back vents under the driver and passenger seats. I am not sure if it’s just my car but trying to push air to the rear floor just seems to limit airflow enough that the car doesn’t cool down as effectively.

 

Thanks. I have OBD Link LX but have not bought the special PID for my current PP. I had it for 2017 PP, but turns out, it does not work for the newer year model. I can't remember seeing the temperature sensor data, but I did not spend too much time on the app. It could also be slightly different from the app that comes with MX+.

One thing I do know is that LX did not stay connected after the car was turned off. I even had a hard time connecting to my 2021 PP for a while.

 

For reference the data I am pulling for my dashboard is:
Hybrid Battery Temperature 1-15
Hybrid Battery Stack 1-4 cell voltage
Hybrid Battery cooling fan intake air temp 1-2
Hybrid battery cooling fan 1/2 drive request
Hybrid battery SOC
Hybrid battery current