HV Battery Rebuild - Cell Capacity and Balancing Help

125F is 52C which definitely sounds too high. If I recall correctly the battery fan comes on low at about 36C and should be running pretty high by about 45C.

Doesn't having the cover off the battery effect the cooling and air flow?

 

52C is indeed high for standard running around town or flat highway use. Not so many mountains in Texas.

I have seen ~50C in some circumstances, once due to my forgetting to discharge the batteries a bit after parking with all green bars from a long downhill run. I came back and the car was hot inside! However, I still could not hear the battery fan come on from the driver's seat, even though I know if I put my ear up to it, the sound is quite audible.

And yes, I would think the battery cover off means less air flow rather than more.

The rebalancer threads seem to try for very good capacity matching. But I would be more concerned about internal resistance readings. Have you checked those out across the pack?

 

Thanks for the info nh70.

I wonder what temperature is required before the fan comes on at high speed (where it's clearly audible). Member 2009prius logged battery temperature and fan voltage and showed the fan comes on at low speed at around 35 or 36 degrees C.

BTW, I also made the mistake one time of parking in the hot sun after a long decent with the SOC at full 8 green bars. When I parked the car the fan was not audibly running (so probably running on low speed), but when I returned one hour later the fan came on at really high speed the instant that I powered on. It even had some sort of driveability issues for the next 10 to 15 minutes after that event. No doubt this was fairly hard on the battery and I've since tried to avoid doing it again.

 

Ken,
Thank you so much for reporting back with an update and summarizing some of the "lessons learned".
Hopefully this will help others in their decision whether to rebuild and how to go about it.

 

I would not mix dissimilar cells in a pack. Even in temperate climates it may cause issues.
I don't have temp numbers handy, but if you have the ability to have similar modules, I would deal with that first.

XT1049 ?

 

Just to add a few numbers to the data: I was out today, and saw a peak battery temp of 49C, with a battery air duct inlet temp of probably ~24C, and the battery fan was bouncing around 8-9 volts, inaudible from the driver seat. At another time the batteries were at 43C, and I turned off A/C, windows down, so the air inlet was a bit warmer. Fan voltage never went above 9V. For those who have the battery overheating/ noisy cooling fan experience, I would guess they are seeing temps well above this.