RegGuheert said:
I agree it is a brutal and impressive test, but the thermal environment is completely different, so those results do not tell anything about temperature rises within the LEAF battery system.
Right, and while I agree that the thermal conditions are different, I believe that this sets a cap to the temperature rise we will see when operating the vehicle.
RegGuheert said:
There certainly IS a temperature gradient between the cell cores and the outer metal case of the car since the power is being dissipated in the cell cores and the thermal resistance is not zero. Agreed, I cannot prove what the gradient is, but I think 5F sounds pretty low, but could be in the ballpark.
Right, but that's the core of our argument. You seem to claim that the cell core temperature is at least 7.5F higher than ambient on average for the life of the vehicle, and I'm of the opinion that it's lower. Perhaps even much lower.
RegGuheert said:
I'm sorry, but I never made any comparison between heat dissipated during QC and driving on the highway. But I will say that I see no reason why temperature rise in the battery could not be higher in city driving if you are accelerating and braking hard. The cooling is less at lower speeds and heat dissipation can be very high.
If you meant to say that it's QC in addition to freeway driving, then I apologize, because I misunderstood that, like you seem to have misread my post about 100 Watt of average dissipated heat.
RegGuheert said:
It sounds as if we are in violent agreement, then! I have proposed a 12F temperature rise to the cell chemistry and you are claiming 10F to the sensors on the cases. Perhaps I wrote something different from what was intended?
Yes, perhaps I misunderstood your post, and I apologize if I did. Also, while my posts might seem argumentative and adamant, I'm just trying to get a better understanding of the car, much like yourself and everyone else on this board.
RegGuheert said:
Please note also that I was talking about a 12F rise from BOTH QC and driving.
Right, that sounds reasonable, and probably even too low. Nissan went on record indicating that more heat is developed when charging than during vehicle operation. I mentioned that before, but I can't seem to find the quote.
Ingineer said:
It's not uncommon for me to see a 5-10 degree F rise in pack temp after a long charge, and that's here in the mild San Francisco Bay Area where my pack almost always starts below 70 degrees.
Yes, great data, thank you Phil! For what it's worth, I can confirm that I regularly see six temperature bars following a level 2 charge in a similar climate. I typically only see 5 bars here during vehicle operation and thereafter, which means that the sensors are reading 72F or below.
RegGuheert said:
Ingineer said:
Note that the temperature readings are what I'm seeing reported by Nissan's Battery Management System computer (Battery ECU) which uses 4 sensors spread throughout the pack to determine temperature.
Thanks for that. Somehow I thought LEAFscan had access to each of the four sensors individually. I guess not. If it somehow combines these, do you know what it does? Average? Peak? Something else?
I believe that Phil answered that in one of his earlier posts, and Leafscan is displaying an average value computed from the four sensors.
RegGuheert said:
Ingineer said:
The internal resistance of my healthy pack is reading 92 milliohms. If my math is correct, This means carefully cruising along at about 55mph (assuming 20kW load) you'll be generating a minimum of 250 watts of heat in the pack. If you drive aggressively, it could easily be well over 1kW. Full throttle driving will create over 5.7kW of added heat!
I have been using 50 mohm for my calcs. Does anyone have any idea what the resistance will be toward the end of the pack life?
This is great! I believe that it's close to the 100 mOhm Tom and I have determined with Gary's meter. If I recall correctly, aging models typically predict similar percentage change for both capacity loss and internal resistance rise. Another thing to note, if I eyeballed it right, then 55 mph is about 0.5C load and about 100W of heat is developed in the pack, 80 mph is about 1C and 360 Watts of heat, and 87 mph is about 1.5 C and 800 Watts worth of heat in the pack.
RegGuheert said:
Ingineer said:
I've noticed I can start out with a pack temp of 70, then take a long drive and return home with it reading only a few degrees higher, but still slowly climbing. It will continue to rise once the car is parked (even when inside a building with cool temps and not charging) and sometimes I've seen it get close to 80 before it starts to cool back off.
O.K. That means that something in the pack was above 80F when you parked. How much above 80F is hard to say without a thermal model.
I think this observation, while anecdotal, could have implications for battery longevity. If you assume that an average vehicle spent only about 15% of its life charging or driving, and it needed twice the amount of time to dissipate the accumulated waste heat, then the cells will spend significant amount of time above ambient.