Cooling the Leaf Battery with Ice, This Actually Works?!?

[knightmb]

To start with, I've known about this "cooling" technique for nearly a decade now. Basically, when "heating" issues first came up with doing multiple QC on the Leaf, the battery temperature always had some "urban legend ways" to cool it down. For the longest time, I've read about the dumping of ice into the central disconnect cavity and while it seemed silly, some people said it worked, others said it was dumb because of the size of the battery and the thermal mass, etc. I have never seen anyone actually try an experiment with measurements to see if it actually does anything.

Well, with the Holiday and some free time, I got another question from a friend asking if the "dump ice on it" they were reading about from some old FB post years ago actually did anything. I told them the battery was so big, it would take a lot of ice to begin with and even then I wasn't sure if it would even make a dent in the battery temperature if it was really hot outside, like anything above +90 F (32.2 C) for example. Today I decided to actually put that to the test and see if it made any measurable difference.

I came into this experiment expecting to fail in a spectacular way. I didn't even think it would move the temperature in the conditions I was testing in because it was so hot outside but it seems there is something to this.

To start, my test Leaf was my 2020 SL Plus. It has the 62 kWh battery pack, so it has the largest thermal mass of any Leaf. Another bonus, it was blazing hot outside and the battery had the entire day to sync up with the air temperature. It was +96 F (35.5 C) outside when I started my experiment and climbing!

I start by opening up the rear, center floor console to access the battery safety disconnect area.
I know this area basically is in line with the top air flow channels, so any water in the area should drain out fairly quick. So I cover the switch with a small zip lock bag to keep out any water and proceed to pour some small amounts of tap water around to make sure the channels are cleared out. This way, any ice melt will drain out properly. The last thing I want to do is form of pool of water that leaks into that disconnect plug.

Next, with the bag still covering the disconnect plug, I fill the entire area up with ice that measures around 0 F (-17.7 C).

As the ice begins to melt, my Leaf appears to leaking everywhere underneath as expected.

Finally, when I quit taking measurements, still had this much ice left before I dried out everything and bolted the covers back on. I just left the rest of the ice in there, it will melt away anyway.

 

[knightmb]

Here are the results. They speak for themselves. I was taking measurements on and off every 15 to 30 minutes. You'll notice that the temperature outside is actually getting hotter as I do this, yet the cooling continues.

I'm amazed this actually had *any* effect at all. If anyone has any free time in their future and plenty of super hot weather with a ton of spare ice to test with. I would be curious if these results are repeatable or if my Leaf is some how special? This actually gives me some ideas for a cooling mod that might actually do something on the cheap anyway...

Notes: There was room for more ice, but I only bought one bag because I didn't think it would matter...

 

[Daklein]

Neat, can't hurt. Easier and cheaper than adding an actual battery thermal system. I respect Nissan for keeping it simple, instead of making it complicated like most every other EV manufacturer. No thermal system works fine an awful lot of the time. Sure, hot climates, parking outside, not so great with DCFC.

Build / 3d print a little bin that bolts on instead of the cover. On a hot weather, long trip with multiple fast charging stops, put a bag or two of ice in the bin. Cool drinks too.

Start the trip from an air-conditioned garage. I'm installing a mini-split in the garage currently.

Next time the underbody battery covers are off, put a layer of reflective bubble 'insulation' between the battery and the covers. On a hot day, pavement is radiating heat up and heating the battery.

 

[knightmb]

I'm building a crude one right now to hold more ice and seal the air so I can drive with it (since it's part of the air channels, can't just leave it open and mess up the air flow) because I've got plenty of hot weather and nearby DC fast chargers to see what happens when you try to mix the two of them together.

The downside is everyone is going to think my Leaf is leaking brake fluid or something all the time. Even funnier, they might think it's leaking gasoline.

 

[cornbinder89]

I'm building a crude one right now to hold more ice and seal the air so I can drive with it (since it's part of the air channels, can't just leave it open and mess up the air flow) because I've got plenty of hot weather and nearby DC fast chargers to see what happens when you try to mix the two of them together.

The downside is everyone is going to think my Leaf is leaking brake fluid or something all the time. Even funnier, they might think it's leaking gasoline.

I bet you could have some fun with that. "Better not park near me, I am leaking gas!"

 

[DougWantsALeaf]

amazing, even a few degrees can translate to a substantially faster 2nd and 3rd DC charging stop.

Did you do a baseline test with no ice during similar periods and outdoor temp perhaps?

Also curious if cooling goes faster when driving with the air circulating the cool faster?

I may try the same with a pile of reusable ice packs later this summer.

 

[knightmb]

amazing, even a few degrees can translate to a substantially faster 2nd and 3rd DC charging stop.

Did you do a baseline test with no ice during similar periods and outdoor temp perhaps?

Also curious if cooling goes faster when driving with the air circulating the cool faster?

I may try the same with a pile of reusable ice packs later this summer.

It was already at a baseline when I started, basically air temperature and battery temperature were in sync. It was sitting level on concrete in the Sun. I usually park in the shade, but for this I figured why not stress the test it to the max.

Not sure if driving helps or hurts yet. Having an open hole while driving would probably not be ideal. Forcing more blazing hot air across the battery, my guess would work against the cooling effect.

I think the cold water helps to spread the cooling across more surface area. Driving might just blast all the water out back and negate this, not sure yet.

My prediction is not moving and having the melt water flow over the battery might work better than driving and having all the hot air flowing around battery and also melting the ice faster and blasting the melt water out the back off the battery case.

My initial concern was cold spotting the middle but it seems the case is good at evenly spreading the cooling effect.

 

[MikeinPA]

My initial concern was cold spotting the middle but it seems the case is good at evenly spreading the cooling effect.

Making the top center of the metal case near 32 deg F will create air convection inside a case with 90 deg F air. With air circulating, cooling spreads through case. But also, densifying the air, pulling in humid outside air, which flows over 32 deg F metal, and condensation inside the case is possible.

If there was a way to circulate dry air from the case, up through tubes in an ice bath, back through a good quality air drier, and back into the case--that could remove some btus.

• Mass of case 800 - 1000 lbs,
• thermal capacity of lithium batteries , 0.5 btu/lb
• = 500 btu per degF change in Leaf battery.
• melt one lb of ice = 144 btu
• 3 lbs of ice per degree F change in battery

It would make more sense to use an air to air heat exchanger duct into the Leaf heat pump. Still put an air drier on the battery side air path. Of course, the middle of the rear stack is still heating up more...

 

[Dooglas]

Wow, you're brave to make your 62 kwh battery pack a guinea pig for an experiment like this.

 

[duncan-s]

With air circulating, cooling spreads through case. But also, densifying the air, pulling in humid outside air, which flows over 32 deg F metal, and condensation inside the case is possible.

A lot of food for thought here. I agree that extreme temperature difference in a small area would almost have to cause condensation especially when there's no airflow, which is exactly when you'd want to use the ice trick.

The question I want to ask is, does the battery pack case conduct heat (or, equivalently, cold) reasonably well even in the absence of airflow? But I guess the fact that some quantity of ice remains after a few minutes is in itself probably an indication that the heat conductivity wouldn't be fast enough to avoid condensation forming and dripping down into the cells.

 

[Chad E. Mo]

It's not clear to me there are any vents in the case to allow humidity ingress. Seems more likely to design the case to handle the thermal expansion of the inside air while maintaining a hermetic seal.

 

[knightmb]

As far as I seen (from a close up view of the pack taken apart), the whole thing is sealed. Even the safety disconnect at the top is setup in a way that water should not be able to get in. I believe even the switch itself that you pull out is water proof, but don't quote me on that as I would have to pull mine out first and inspect it before making that claim. That's why I covered the switch with a bag regardless when dumping ice around.

Years back, someone posted a picture of the Nissan battery completely submerged in a shallow baby pool to show how water tight it was, but I'm not sure where to find that one.

 

[knightmb]

I did a driving test today to see if the cooling benefits are too slow versus pack heating while driving. I was not expecting much but was surprised yet again.

First, my experiment is just driving a 50 mile round trip. The driving ranges in speeds from 55 to 75 mph and because I've made this trip many times, I have a good understanding about how much it raises the pack temperature. My driving conditions are cooler today (which I am not complaining since we had +100 F (37.7 C) temperatures the last few weeks), so I start my trip with the air temperature around 90 F (32.2 C), the battery pack itself has been sitting in the heat all day again. Its temperatures at the various sensors range from 90.6 (32.5 C) F to 92.8 F (33.7 C) which is a pretty close match for the high temperatures this day and just sitting outside in the hot weather.

I get a LeafSpy screenshot to record the starting temperature. I open up the safety disconnect switch cavity again and fill it with ice once again. Same temperature as before 0 F or (-17.7 C). I bolt the cover back down and immediately take off for my driving trip.

About an hour in the trip, I get a LeafSpy screenshot measurement. All of the temperatures have gone done, no way!
Usually by this point, I know the battery should be at least close to 95 F (35 C) It actually cooled during the entire trip, which is the complete opposite of what I was expecting.

But... the good readings did not last long. When I arrived at my destination, I noticed that no more water was "leaking" out the back anymore. So I took another LeafSpy screenshot and noticed the temperature starting to creep back up. I'm fairly certain that having hot air blowing over the ice the entire time has basically melted everything and probably blown all the ice melt water out the back as well.

During my trip back, I see the temperature was creeping up again. I figured the ice was certainly gone. Probably within the first hour of driving. Nothing wrong as it's normal for the temperature to do this anyway.

Now that I'm finally home, I get a final temperature reading. Normally, all the sensors would easily be +100F (+37.7 C) at this point, even higher if the outside air temperature was even higher. Basically, negated about half the temperature increase with the ice. When I arrived at home and after taking the temperature screenshot, I turned off the Leaf, then unbolted the cover to look inside. Yeah, all the ice is gone and so is all the water and it is dry as a bone in that cavity.

Conclusion: Ice works for trips too, but it doesn't last long. The hot air flowing through the cavity quick melts the ice and the air flow is probably also blasting all the ice melt out the back too.

Data Issues: My ice measurements are being eyeballed full manually, so I know I'm not putting in the same amount every time I do this, so there can be big variations in my data.

Future Improvements: Mainly, I just wanted to spitball some easy test to see if the ice was having any effect and I can see that it is to my surprise. I can't really quantify it yet because I need to do test with a very specific amount of ice and maybe plan some real test routes that are easy to duplicate. I also wanted to try doing some QC test with the ICE to see if it can negate the heating since I already have a lot of good data on how much my pack temperature increases during a QC session to compare with.

 

[duncan-s]

As one last point of devil-engineer's advocacy ... in general the sealed-ness of a container isn't relevant to whether condensation can form in it, the exceptions that I can think of offhand being, maybe it was sealed under conditions of controlled low humidity, or there's just hardly any room for air in there in the first place, sort of like how vacuum sealing food prevents freezer burn.

But there's a lot I don't know about this hardware. If icing the top works (which you've demonstrated) and doesn't hurt anything, then that's all that matters.

 

[knightmb]

I think if I was using something colder like dry ice (which is like -100 F or -73.3 C) then I would have more concerns about moisture buildup as well. I've driven through mountains before where it was hot on the valley and freezing up in the high elevations. My guess is Nissan has planned for such a thing where a hot pack starts to plow into freezing cold air and must have taken precautions to avoid any moisture from getting into a place where it shouldn't. That's my logic for using just regular ice anyway. Seems that very early on, some Leaf others would have had similar issues and either I'm just real lucky or Nissan has already engineered something for this. To be fair, I'm just doing it now, people were already doing this a decade ago, but they only posted vague stuff like "I didn't gain a temperature bar" which is not specific enough for me.

That's why I didn't think much about this or else I would have tested this long ago back in my Gen 1 ownership days.

 

[Chad E. Mo]

Umm... did we lose a few posts? The site was up and down, and it seems we have data loss.

 

[MikeinPA]

Yep, I got a comment deleted!

 

[leaf4eva]

Ice might be a bit dangerous. Water can get inside enclosed spaces indirectly through condensation, no matter how water-tight it is. Kind of like how you shouldn't defrost something directly in the sink or on a kitchen counter, since because of the extreme temperature difference, air will condense underneath and drip water into the timber cabinetry below.

 

[kmcmahan]

To start with, I've known about this "cooling" technique for nearly a decade now. Basically, when "heating" issues first came up with doing multiple QC on the Leaf, the battery temperature always had some "urban legend ways" to cool it down. For the longest time, I've read about the dumping of ice into the central disconnect cavity and while it seemed silly, some people said it worked, others said it was dumb because of the size of the battery and the thermal mass, etc. I have never seen anyone actually try an experiment with measurements to see if it actually does anything.

Well, with the Holiday and some free time, I got another question from a friend asking if the "dump ice on it" they were reading about from some old FB post years ago actually did anything. I told them the battery was so big, it would take a lot of ice to begin with and even then I wasn't sure if it would even make a dent in the battery temperature if it was really hot outside, like anything above +90 F (32.2 C) for example. Today I decided to actually put that to the test and see if it made any measurable difference.

I came into this experiment expecting to fail in a spectacular way. I didn't even think it would move the temperature in the conditions I was testing in because it was so hot outside but it seems there is something to this.

To start, my test Leaf was my 2020 SL Plus. It has the 62 kWh battery pack, so it has the largest thermal mass of any Leaf. Another bonus, it was blazing hot outside and the battery had the entire day to sync up with the air temperature. It was +96 F (35.5 C) outside when I started my experiment and climbing!

I start by opening up the rear, center floor console to access the battery safety disconnect area.
I know this area basically is in line with the top air flow channels, so any water in the area should drain out fairly quick. So I cover the switch with a small zip lock bag to keep out any water and proceed to pour some small amounts of tap water around to make sure the channels are cleared out. This way, any ice melt will drain out properly. The last thing I want to do is form of pool of water that leaks into that disconnect plug.

Next, with the bag still covering the disconnect plug, I fill the entire area up with ice that measures around 0 F (-17.7 C).

As the ice begins to melt, my Leaf appears to leaking everywhere underneath as expected.

Finally, when I quit taking measurements, still had this much ice left before I dried out everything and bolted the covers back on. I just left the rest of the ice in there, it will melt away anyway.

Yes, that will work. I did something similar a couple of years. I attached micro-fiber cloth to the upper case of the battery with magnets. I ran soaker hose across the top and pumped distilled water to it with a metering pump. I run it during hot weather and it works. I have been doing this for about 3 years. My biggest concern is rust and corrosion. I should probably drop the battery and check it about now. I pump when the car is running.

 

[knightmb]

It seems everything I've posted here is intact, so glad, that was a lot to type.

Right now, I'm testing to see how much "ice" I can pack into that cavity. I started with 5 lb (2.3 kg) bags of ice you can buy at the local stores, now I've moved up to 7 lb (3.2 kg) bags of ice and it still has some room left. I'll see at what point it will max out the space. My guess is probably going to be the 10 lb (4.5 kg) bag of ice.

I'm running another experiment today with a 90 F (32.2 C) battery in +92 F (33.3 C) heat with this 7 lb bag of ice to see what effect it has since this is most ice I've packed in so far.