Battery Cooling


TCMB371

The Silent Assassin
Forum's Sponsor
Location
Temecula, CA
External cooling of the pack will only help so much. In fact, i plan on doing back to back tests with my mister fan to see how much of an effect on battery temps externally cooling the pack actually makes. @Mark911 said he had cooled wet towels blanketed over the pack when he was having a pro ride his bike for slamfest a few years ago, and it didn't help all that much. In my experience, though, externally cooling the pack does help lower the temps a little bit. I'd like to quantify the effect via MultiTool, though.

What would really be awesome is if we could redesign the battery packs to allow for actual cooling of the cells inside. Mark's idea was to pipe cooling channels weaving in between the cells, a la Tesla. You'd have the loop exposed to the outside of the pack so that you could hook up water lines to it. The idea is that you'd "precool" the pack before a ride to give yourself a higher thermal ceiling, of course draining the system before you ride so that you do not carry around all that water weight. If you start off cooler you'll be less likely to heat the pack up to the thermal limiting temperature of roughly 70*C.

I got into reading more about cooling 18650 cells and it seems like the most efficient way is to cool the end terminal tabs of the cells rather than the sides of it. To this point, perhaps we could simply fabricate a water block that lays on top of the PCB that has individual heatsinks down pressing on each cell terminal. We'd have to be very careful not to cause a short, though.

 

Sumik

Well-known member
Location
Czech Republic
What about an external "pocket" that could hold dry ice? Could be in front of the battery between the verticals of the battery cage.
Interesting idea! The question is if cooling the external case of the battery will really help cooling the cells. And of course it would cool the sides of the cells and not the terminals - see the video from TCMB371 above. If it would help, there are several options how to do it. For example a 1 l plastic tank of water below the batery, a screen washer pump and 2 nozles which woud spray the battery with small water droplets in a defined time intervals. The evaporation heat of 1 l water should be enought to cool the battery case for at least 30 minutes.
 

TCMB371

The Silent Assassin
Forum's Sponsor
Location
Temecula, CA
Interesting idea! The question is if cooling the external case of the battery will really help cooling the cells. And of course it would cool the sides of the cells and not the terminals - see the video from TCMB371 above. If it would help, there are several options how to do it. For example a 1 l plastic tank of water below the batery, a screen washer pump and 2 nozles which woud spray the battery with small water droplets in a defined time intervals. The evaporation heat of 1 l water should be enought to cool the battery case for at least 30 minutes.

This is exactly what the mister fan + bucket of water accomplishes, but its a stationary option while in the pits. I think what you're describing is something that could be used while riding. Interesting idea. You have to keep in mind though that it would add weight to the bike and it would taper off as the water used up. I guess the weight change would be similar to a gas bike using gasoline as it operates.
 

Sumik

Well-known member
Location
Czech Republic
This is exactly what the mister fan + bucket of water accomplishes, but its a stationary option while in the pits. I think what you're describing is something that could be used while riding. Interesting idea. You have to keep in mind though that it would add weight to the bike and it would taper off as the water used up. I guess the weight change would be similar to a gas bike using gasoline as it operates.
The cooling heat of 1 l water is enough to cool the whole 5.8 kWh battery pack until it's empty. Assuming the battery efficency during discharging is at least 90 %, max. 10 % will be converted into heat, which is about 0,6 kWh. Evaporation heat of 1 l water is about 0,7 kWh which is 4 times more than the sublimation heat of dry ice. I don't have any concern regarding the weight change as it's just 1 kg and it's below the center of gravity. But you are right it's about 1.5 kg extra weight to the already havy bike :cautious: and I'm not sure if it helps cooling the battery case only..
 

Mark911

Well-known member
Location
Corona Ca
Water (unless under vacuum) evaporates way to slowly at those temperatures to do much good from an evaporation standpoint but it does cool the housing which pulls more heat out of the pack (within limits). To be effective you'd need way more surface area, like using water spray into a air-to-air intercooler. The problem is that our cells themselves don't like to give up the heat they produce, particularly in non-steady state conditions (which is just about all the time in MX). You need quite a delta T between the cell and the working fluid to transfer any significant amount of heat and even then it's only effective through a limited surface area (ie, the negative cell end). It's quite the design challenge.
 

querlenker

Well-known member
Location
Germany
If you start off cooler you'll be less likely to heat the pack up to the thermal limiting temperature of roughly 70*C.
Thermal limiting starts earlier from the data I have and it’s unequal heat distribution in the pack (about 10-12 degree) which is a problem. Some spots are above 60 degree Celsius when others are below 50 for example.
 

Mark911

Well-known member
Location
Corona Ca
It's everything, too low temp, too high temp, too much temp gradient, too quickly, etc, etc. Until we fully understand the algorithms within the Firmware all we can do is speculate based on indirect evidence (our ride files). Even the amount of limiting is variable, and there's a low limit and a high limit. I haven't studied my data to that extent but I'll guess that the low limit affects/truncates lower rpm current and the high limit, well, high rpm current limitation.
 

Jmazz274

Member
Location
Salzburg
To try extend my performance window on the Mx track (I usually reach thermal limiting warning within about 10min at race pace), I have mounted some skid plate foam along the front surface of my battery... 1) to keep mud from caking onto it and trapping the heat in, and 2) to be able to hold moisture to hopefully enhance the air cooling effect...

Has anyone tried anything similar before? I’ll be testing it out at a local Mx race next weekend to see if there’s any improvement/extension of full power riding time.. before the dreaded amber light goes on
 

Philip

Administrator
Staff member
Location
Ann Arbor, MI
The MX is not well-suited for motocross in summer temperatures. My approach was to sell it and buy an MXR. @Mark911's approach was to build a new bike.

If I had to keep the MX, I would probably install a water mist sprayer onto the bike and keep it spraying onto the battery while riding/racing. Then switch to a larger stationary external mister while parked and/or charging.
 

VINSANITY

Well-known member
Location
Texas
I though it would be efficient to have external pockets where you could place dry ice pellets - very small 1” squares that you could drop in - space them so you don’t over cool an area - you would have to have a type of material that could resist the extreme cold at those spots probably material like a fireman jacket I was thinking where you could see together a jacket for the existing battery and Velcro it together
 

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