Hot temps and Prius battery questions

Where would the difference lie, between BT2 (Cell Temperature Sensor 2, from PriusChat's spread sheet) and BtT (Traction Battery Temp, from ScanGuage's website). I'm gleaning from Robert Holt and HTMLSpinner that BT2 is going to read higher.

 

There are three battery temp sensors; BT1 is closest to cooling fan and electronics, BT2 is in the middle and BT3 is at the other end. BT2 is typically the hottest which makes sense being in the middle. The cooling fan speed is controlled by the hottest sensor. BtT is the temp of the cooling air as it is drawn in from the cabin vent and blown through the batteries. It is located in the cooling duct between the cooling fan and the first battery module.

 

Temps over 45C cause accelerated damage to the NiMH batteries. Besides the AZ thing, how do you drive to manage such high HV temps? Have you checked the fan?

 

I have one "gauge" slot dedicated to BFM, and supposedly the range is 0-6, but the max we've observed is level 4 when the bt2 had spiked to 47 Celcius after the car was parked after mountain hot weather driving for several hours. Have not seen BFM of of 5 or 6.

 

I have a similar situation parking in the sun all day. I see the similar 5 minute delay after start before the cooling fan starts.

 

Hell I'll never get the fan to go on. Had a high of 30C on BT2, and 0 for BFM. It has gone on, I see a few seeds and bugs in the filter I have at the inlet.

 

This is weird. Is the cabin air temp initially too high to cool the battery?
From the description, I would be surprised if the battery made it before warranty expired, which would be actually a good thing.

 

Good video. I experienced overheated battery only once when my wife drove the car very hard (the only way she knows to drive) and then parked in full sun in the middle of day. When I drove it later, I had the same thing, no battery assist, ICE revving high and not turning off. Cooling fan on high speed (I don't remember the 5 min delay though). The behavior persisted for entire 30 min drive and somehow the fan was not able to bring the temp down despite AC on. Sounds like the battery is very susceptible to heat soak.

For this and other reasons, I go out of my way to park in shade as much as I can. Not always possible, but I had no other episodes of overheating since.

 

For me the cabin temp is high, high 90's or low 100's, and to start I have the windows open to expel the superheated air. It takes a couple of minutes of driving to cool down the cabin to the point the AC is beginning to blow cold air. Even after closing the windows and the AC beginning to cool the cabin the cabin temps are still in the high 80's.

It seems that right about the 5 minute mark after starting the cooling fan will come on and begin cooling the batteries. It appears to have a 5 minute timer under these conditions and not necessarily a cabin temp setpoint. As Rick points out when the cooling fan does come on it is at minimun speed for about 1 minute before it begins to ramp up to set speed.

 

Try your test with A/C recirc and then flow through. My experience was flow through mad it significantly cooler.

 

[QUOTE="Feri, post: 2052681, member: 77885]Try your test with A/C recirc and then flow through. My experience was flow through mad it significantly cooler.[/QUOTE]

My experience has been that if the cabin temp is close to setpoint then the outside air does appear to help with the battery cooling to some degree. If it is really hot outside and the cabin temp is above setpoint then if you switch from recirc to outside air there is an initial improvement in BtT but then the cabin temp begins to rise with the additon of hot outside air. The rise in cabin temp more than offsets the outside air flow. Not to mention the heavy increase in AC watts as the compressor tries to cool the outside air.

For my particular daily commute keeping AC in recirc works best for me.

Of course YMMV.

 

Temps aren't anywhere near as hot here in Minnesota, but the videos I've started to make at least provide a basis for understanding the elements at play with respect to heat... like this one:

 

I don't question your observations, (I'll re-test mine once it warms up here.) but I'm wondering where else air vents from the vehicle if not through the wheel well, and where does fresh air, to replace the evacuated air, come from if not through the front ventilation inlets?

 

I export Torque data into CSV format...
import it into a mail-merge template in Word...
save the merge results as a DOCX document...
convert that to a PDF document...
export each page as a PNG file...
build an photo album in PowerPoint...
export that as a video file.

It's surprisingly simple, despite sounding rather complex. The catch is, you need quite a bit of computer power and software to accomplish that.