Battery temperature management

[Malm]

Evolution of pack temperature for 1 hour and 21 minutes, time period in which two quick charges were executed, with the car off all the time. When it started the pack temperature was 19.4 º C and the car turned on maximum ventilation, but no AC. This value rose rapidly, reaching 21.8 ° C at the end of fast charging. During this period, the i-MiEV has maintained maximum venting always tied to the pack, but never turned on the air conditioning. After 14 minutes and 58 seconds, time when charging finish, the fan also turned off. The temperature of the pack continued to rise up to 22.5 ° C, reaching this value 10 minutes after the end of the 1st charging. In the second temperature load, in the beginning, it was 22.2 º C, rising only to 22.3 ° C, a value that remained unchanged for 2 and a half minutes, and by the end of the charge, temperature remain at 22.2 ° C. Again, always with ventilation but without air conditioning. After the end of the charge, due to cessation of pack ventilation, the temperature rose within 10 minutes up to 22,6 º C.

BUT if the initial temperature of the pack is 29 º C, well, things are very different. The air conditioning is immediately connected together with maximum ventilation and the highest value reached was 29.2 °C, in the beginning of the charge. After, gradually decreased to 27 º C. A second fast charge done and temperatures fell from 27.3 º C to 23.7 º C (yes, 23.7 º C), always with the air conditioning on.

With all this, I was curious to find what causes the air conditioning turning on and I caught the exact moment the AC light turns on, being precisely at the time when a cell reaches 31 º C. The temperature of the pack was 26.8 °C when it happened.

http://www.youtube.com/watch?v=r3GePlW1P4E

 

[JoeS]

Malm, thank you for posting the data and analyzing the numbers. Must say, Mitsu is indeed being quite conservative with the iMiEV pack. Can't help wondering if they've had some misgivings about not including active pack cooling in all the iMiEVs. Not to worry, going forward, since all the 2014 iMiEVs will have CHAdeMO, all the cars will have active cooling as standard.

Now, if 31degC (88degF) is the magic number, does the active cooling turn on while simply driving around on a hot day and a cell reaches this temperature?

 

[Malm]

"Now, if 31degC (88degF) is the magic number, does the active cooling turn on while simply driving around on a hot day and a cell reaches this temperature?" No. So many times I drove with cells above 31º C, so many times I made slow charges with cells above 31º C. I live 100 km of the near beach, and i take it with me in the summer, because I pay 1 € of electricity instead 20 € of gasoline. Outside temperatures easily go up 30º C here in the summer. I never see that light on, unless i turn it on (obviously not for the pack) or in some quick-charges, when the pack is hotter.

I think that my inner cells are now weaker then the peripheral ones because had experienced temperatures above 40º C in the last 3 summers. Peripheral cells of the pack are usually colder, and i see it day by day, even in winter. So heterogeneous degradation, in my i-MiEV, clearly. A thing that we would like not to happen, because the car will stop when the weakest cell reaches 2,75V (i think, one time happened to me, the only time that I depleted the battery to the state that it don´t move anymore since I have canion).

The true is that my car can stop now with something like 18/19% of SoC. Shows turtle for a second and that's over. But i can show you a screenshot of my battery at 20% of SoC with cells very well balanced to. How can this happen? In the first, SoC evaluated by the car is incorrect, and it happens if the car gives me, after a full charge, 100% SoC and i don't let it rest for sometime until it reaches 20%. But usually, after a full charge, i only have 95,5% of SoC, and if I stop for one or two hours after driving 30/40/50 km, it takes me another 5%, and then it will stop, not at 18/19% but at 8/9% (and this time with a consistent turtle). I know this behavior and now I can even play with it, maybe I can show here my battery terrible unbalanced at 40/50% SoC, only because i know how to fool it with his SoC. I think my i-MiEV difficulty of evaluating his SoC is because of having some cells now weaker, but that charge to 4,1 V like the others. I think now, after almost three years and 60.000 km, i do less 15% of the distance then when new.

 

[RobertC]

Just home with mine tonight. 2014 Blue with USB for 23k even, including delivery plus got the great Mitsu finance package. This one of only two in Arizona. Let's hope my battery doesn't bake too much.

Congratulations!

If I lived in Arizona, I would make the reversible modifications (no warranty issues) that would result in some of the cooled air from the A/C being directed down into the battery compartment while driving, not just while Level 3 charging. I would then get CANion to monitor battery cell temperatures. When these temperatures exceed a certain level, I would engage my modified cooling system to direct cool air to the battery pack. I think this would minimize the degradation that is almost certain to occur in hot weather.

My i-MiEV doesn't have the Level 3 charging capability that makes this modification possible, so I have not done this to my i-MiEV (although, I doubt that my battery cell temperatures get too hot during short drives around Honolulu). If you have any questions about this modification, just ask in this forum for more information.

I would not make the modifications that would result in some of the cooled air from the A/C being directed down into the battery compartment while driving.

My tests using CaniOn showed that even directing all of the cooled air from the A/C to the battery during driving only lowered the temperature of the externally located battery temperature sensors a few degrees. Air cooling the i-MiEV batteries can only be marginally effective since the batteries do not have a heat sink to dissipate their heat. Additionally, frequently blowing outside air into the battery pack may lead to early corrosion of the battery management circuitry, and leaving the vent to the battery pack constantly open may lead to dirt and dust migrating to the battery pack from the i-MiEV's cabin.
Even if you drive your i-MiEV 60 miles a day at 30 mph, and you air cooled your battery constantly while you were driving, you are still only air cooling the battery 2 hours a day or about 8% of a 24 hour day. The i-MiEV battery temperature is typically the same as the ambient temperature. A more effective way to keep the i-MiEV battery cool is to try to control the ambient temperature the other 92% of the time.
Here is some test data for the i-MiEV's LEV50 battery capacity for different temperatures:

Taken from the following technical report:
http://www.gs-yuasa.com/en/technic/vol5/pdf/05_1_021.pdf
This data represents 1000 times discharging the battery to 2.75V. The lowest my battery has been discharged is 10.5% (the turtle) and the lowest cell was at 3.66V. Also, this data represents charging the battery at 50 amps. I typically charge my battery at Level 2, which is about 7.6 amps according to CaniOn. Also, 45 degrees Celsius equates to 113 degrees Fahrenheit. These tests say that the battery was charged at 45 degrees Celsius, meaning ambient temperature, so that the battery actually got hotter charging at 50 amps.
To date, we i-MiEV owners do not have any data on the remaining capacity of our batteries. We also do not have any data on the difference in remaining battery capacity for i-MiEV's operating in colder and hotter climates.
Also, when our batteries have reached the end of their warranty at 100,000 miles, we will be able to replace them. A new Nissan Leaf battery is currently $5,500.00 with the return of the old battery. If you put 15,000 miles a year on your i-MiEV, it will take you over six years to reach 100,000 miles.
I would recommend the following for caring for your battery:
1. If possible, keep your i-MiEV in an area where the ambient temperature is not excessive. Park in the shade if possible, or in a temperature controlled garage.
2. Do not repeatedly charge your battery when it is at or near full charge.
3. If you are not going to use your i-MiEV for an extended period of time store it with 2-4 bars charge.
4. Fully charge your i-MiEV by Level 1 or Level 2 charging at least once every 2 weeks.
5. At least once every three months recharge your i-MiEV by Level 1 or Level 2 charging from 2 bars or less to full.
6. Normally charge your i-MiEV using Level 1 or Level 2. Use Level 3 DC Quick Charging only when you need extended range.
7. Don't use maximum power (press the accelerator to the floor) when your battery charge is low.
8. Don't worry about the battery. The i-MiEV is loads of fun to drive. Enjoy it!

 

[JoeS]

RobertC, hope you don't mind that I took the liberty of moving your post over to this thread. I'm still trying to digest your argument against providing the battery pack with cooling air - especially in Arizona where road surface temperatures are often > 110degF (43degC).

 

[Malm]

RobertC - "I would not make the modifications that would result in some of the cooled air from the A/C being directed down into the battery compartment while driving."
"My tests using CaniOn showed that even directing all of the cooled air from the A/C to the battery during driving only lowered the temperature of the externally located battery temperature sensors a few degrees."

It depends on the speed you drive the car. In flat terrain, at constant speed of 40/50 miles/hour, I think cooling the battery will cause a drop of 2 ºCelsius or 3 ºC at the end of a 40 miles trip. Without cooling, they will be something like 4 ºC hotter. This is what I think for what I see in my fast charges.

"Additionally, frequently blowing outside air into the battery pack may lead to early corrosion of the battery management circuitry" Yes, we have to chose between corrosion and degradation. So, maybe if you leave near the ocean, you should not blow air into the battery, but if you live in Arizona, maybe blowing cold air is the best choice.
"and leaving the vent to the battery pack constantly open may lead to dirt and dust migrating to the battery pack from the i-MiEV's cabin." Maybe it's possible to open it only when we are doing it, and keep it close the rest of the time.

For climates as the ones of Arizona or Australia, in Summer, when the battery is over 40 ºC, I think blowing cold air will be the best choice.

 

[selmateacher]

I own a 2017 MiEV, has the Battery temperature management system changed from an AC/ fan to a liquid pump, pumping coolant through the battery pack? I ask this because when I charge my MiEV, I do not hear the AC fan system running as I do for the 2016 models, but instead hear a small water pump and the sound of flowing liquid though a hose. Thank you.

 

[jray3]

I own a 2017 MiEV, has the Battery temperature management system changed from an AC/ fan to a liquid pump, pumping coolant through the battery pack? I ask this because when I charge my MiEV, I do not hear the AC fan system running as I do for the 2016 models, but instead hear a small water pump and the sound of flowing liquid though a hose. Thank you.

I'd place a 9:1 bet that nothing physically changed. The traction battery fan cycling for a couple of seconds at the beginning of each charge was unnecessary, and perhaps they finally killed that software. (Not like the hydrogen should be vented prior to closing a contactor, which was lead-acid thinking.) We all have the water pump that pushes water through the drive inverter and battery charger, then through the radiator up front. Only problem is that the heat sink for the battery charger is on the BOTTOM of the case, and actually does very little cooling.

 

[Phximiev]

RobertC - "I would not make the modifications that would result in some of the cooled air from the A/C being directed down into the battery compartment while driving."
"My tests using CaniOn showed that even directing all of the cooled air from the A/C to the battery during driving only lowered the temperature of the externally located battery temperature sensors a few degrees."

It depends on the speed you drive the car. In flat terrain, at constant speed of 40/50 miles/hour, I think cooling the battery will cause a drop of 2 ºCelsius or 3 ºC at the end of a 40 miles trip. Without cooling, they will be something like 4 ºC hotter. This is what I think for what I see in my fast charges.

"Additionally, frequently blowing outside air into the battery pack may lead to early corrosion of the battery management circuitry" Yes, we have to chose between corrosion and degradation. So, maybe if you leave near the ocean, you should not blow air into the battery, but if you live in Arizona, maybe blowing cold air is the best choice.
"and leaving the vent to the battery pack constantly open may lead to dirt and dust migrating to the battery pack from the i-MiEV's cabin." Maybe it's possible to open it only when we are doing it, and keep it close the rest of the time.

For climates as the ones of Arizona or Australia, in Summer, when the battery is over 40 ºC, I think blowing cold air will be the best choice.

I think this Arizona author must have read this forum, given her Leaf traction battery cooling mod!

https://cleantechnica.com/2019/01/06/40000-miles-with-the-2018-nissan-leaf/