HV Traction Battery Failure and what else? (Torque screenshots)

No matter what generation, always start counting from the most negative end of the pack.

For Gen 2, the most negative end is farthest away from the computer.

 

"Always" can be a tough statement to defend.

On the first generation Prius battery the count started at the positive end which was next to the computer.


I used to think that the positive end of a pack was always on the right side. Then I opened up a Prius C pack.


There are still lots of Lexus batteries and other brands that use Prius modules that I have not yet opened up. I will not assume any convention is followed across all batteries.

 

Well said.
I retract my "always" statement.
Thanks for calling me out in that.

 

Can anyone offer an explanation for why Toyota used a different bolt for this one particular HV battery pack mounting hole?

-Greg

As an electronic design engineer I ***cannot*** offer any “electrical” reason for block 5 to have a higher failure rate due to its proximity to the wires leading to the safety plug. All of the battery blocks are electrically “in series” which means ***exactly*** the same current (I - Amperes) flows through each block in both directions: charging or discharging.

A more plausible explanation is that different block locations inside the battery pack have different long-term operating temperatures due to variations in the rate of cooling air flow. A temperature rise of 10 degrees doubles the rate of chemical reactions. Over time a slightly higher operating temperature will shorten the life of the battery module. Also, as an individual cell ages it’s internal resistance will rise which leads to greater “self-heating.”

There are three temperature sensors embedded inside the HV battery pack. But these monitor the temperature of the nearby cooling air. There aren’t any sensors which directly monitor the actual temperature of each block. That would be an interesting project for a geeky person to try: Place a temperature sensor into direct physical contact with each of the 28 individual NiMH modules.

-Greg

 

It's called the grounding bolt. The threads are cut to make a better electrical connection. The battery and car will not function without a good ground between the battery case and body.

 

Thanks! That makes total sense to me. The hole in the car body would have been unthreaded and slightly undersized. When the special thread-cutting bolt is installed the first time it will have a very tight fit, thus assuring a long lasting low-resistance ground connection.

This also explains why this one bolt is a tighter fit than the other ones.

I tend to use permanent markers to label special fasteners and the holes they go into. I also take photos prior to, and during the disassembly process. This saves me a lot of time and trouble.

-Greg

 

Interesting: This is the first photo I’ve viewed of a Prius C pack. It has only 10 blocks (20 NiMH modules) rather than the 14 blocks (28 modules) of a standard Prius pack. Therefore the Prius C pack output voltage is lower (144V vs. 201.6V). And total instantaneous kW output at 100A load is 14kW for Prius C vs. 20kW for the standard Prius. Perhaps Toyota decided this was sufficient for a smaller/lower weight car?

-Greg