Dr. Prius results, pack health

Ran Dr. Prius on our 2007 today.

Just watching the pack readings showed that #7 was usually the lowest voltage, but only by a tiny amount. The internal resistances were all either 28 or 29 (not sure what the units were.)

The life expectancy test was actually better than I expected (for this original battery) with 56.37% capacity. (Seriously, 4 decimal places, like there is really that much precision in this measurement?).

The full battery test flagged these issues (non-issues not shown):

battery running warm
upper voltage balance
poor balance block #1, #2, and #11

For the temperatures back on the main screen, just sitting there, it showed 111.9, 116.8, and 111.1 for the three readings. Ambient was around 70F, and this was just after having driven it. I have never cleaned the fan, perhaps that would help. But I suspect the greater temperature in the middle is related to electrical characteristics of the cells rather than air flow. (Side note. My son and his dog are staying with us, and that dog sheds constantly. Despite never once having been in the car I'm constantly finding its hair on the seats and carpets. The interior is cleaned periodically, but some of that hair might have got into the fan or battery.)

No idea how the app came to the balance conclusion regarding those blocks. Just watching the display they don't seem to be particularly high or low (as opposed to #7, which is usually the lowest). Perhaps it has something to do with the variation on the block? Whatever, I do believe there is a balance problem because it sometimes runs the motor when the display shows all green (minus one) bars, and it sometimes drops the voltage suddenly and starts upwards again, which looks like the recalibration events did on the Honda Civic Hybrid I used to own.

Regarding pack balance: in the Prius, is a long drive on the highway good, bad, or no different than any other usage? I have not driven it for more than 20 minutes at a time on the highway for the last two years. Next week though, I have to drive to the SF bay area and back, which is ~450 miles each way, up and down at least one pretty steep grade. (Either the Grapevine or the Cuesta grade, depending which way I go.) I would hate to see the pack go terminally out of balance halfway up or down either one of those!

 

Those are temperatures, not voltages. From what I've read the center temperature is usually higher than the ends.

 

Had some time today to see what pack temperatures were like at highway speeds. Warmed the car up by driving it for 20 minutes at an average of about 65 mph with an ambient temperature of about 75F. Then exited, found a safe place to park for a few minutes, plugged in the OBD2 adapter and fired up Dr. Prius. My wife read it while we drove. The pack temperature was about 100F. Drove it another 20 minutes back the other way, at similar speeds and temperatures. The temperature went up and down a bit but peaked on the highway with one reading of 105F. (Note that due to the topography of the region the first 20 minutes was somewhat downhill, that final 20 somewhat uphill.) Interestingly, after exiting and driving about a mile on suburban streets it went up to 108F. It still seemed to be rising slowly when we were stopped, but it was time to go grocery shopping so the experiment had to end there.

Those temperatures don't seem alarmingly high to me, although ideally I think they would have been much closer to ambient. It was interesting that the temps seemed to go up at lower speeds. While that might just have been from extra heat generation during charging and discharging, I do wonder how much might have been due to the absence of the slight vacuum near the rear of the car at highway speeds. Perhaps that is enough to pull more air through the pack than the blower was managing alone. CFM always falls when the pressure a blower is pumping into rises, and vice versa.