Air-cooled for 18650 Li-ion battery pack

[eMark]

Here is a battery pack of eBike, have properties is 72V 68Ah. Here is a picture outside of pack:

Assuming it's 20S do you realize how many 18650 cells would have to be in parallel to arrive at 68Ah? Do you realize it may be impossible to cram that many 18650 cells into that enclosure. If each 18650 cell is rated at 3400mAh wouldn't it take 20 in parallel to achieve a 68Ah rating. If 21700 cell's rating was 5650mAh it would take 12 in parallel to achieve a rating of 68Ah. If 4680 cell's rating was 8500mAh it would take 8 in parallel to achieve a capacity rating of 68Ah.

If there were four hundred 18650 cells in that enclosure it would be possible to achieve a battery pack capacity rating of 68Ah ... if each 18650 cell capacity rating was 3400mAh (20S20P = 68Ah). Is it possible to cram four hundred 18650 cells into that 72V (20S20P) 200 DAT.BIKE battery pack enclosure that's pictured below ...

What makes you think it's a 18650 battery pack? Even if it were possible the cells are so close together making passive airflow cooling INEFFECTIVE! Furthermore each of the tightly packed 18650 cells may be wrapped in a fiber cushioning sleeve making even forced airflow cooling next to IMPOSSIBLE!

Are you 100% sure that 72V (20S) battery is rated at 68Ah? Are you 100% sure that battery uses 18650 cells?

Still there is the issue: if your cells are getting hot enough to need cooling, you're abusing them. Use more cells, or cells with a higher current rating.

Thank you for your reply.
you mean the best solution is control the power of battery system, right? instead of cooling it first ?

Yes and YES! ... being that passive air-cooling is NO solution and NOT necessary (Just My Opinion). That 200 DAT.BIKE was NOT designed for endurance performance racing, but rather for casual urban use (as you are well aware) with only intermittent peak performance like when passing, arriving at your destination on time, etc ... NOT for competitive endurance racing ... Xception being unlimited budget for buying replacement battery packs .

Me thinks the actual battery pack is 20S10P with capacity rating of 34Ah. It may be possible to cram two hundred 18650 cells into that enclosure ... thus the name 200 DAT.BIKE ... even so forced air-cooling is NOT practical.

 

[nhattan12]

Here is a battery pack of eBike, have properties is 72V 68Ah. Here is a picture outside of pack:

Assuming it's 20S do you realize how many 18650 cells would have to be in parallel to arrive at 68Ah? Do you realize it may be impossible to cram that many 18650 cells into that enclosure. If each 18650 cell is rated at 3400mAh wouldn't it take 20 in parallel to achieve a 68Ah rating. If 21700 cell's rating was 5650mAh it would take 12 in parallel to achieve a rating of 68Ah. If 4680 cell's rating was 8500mAh it would take 8 in parallel to achieve a capacity rating of 68Ah.

If there were four hundred 18650 cells in that enclosure it would be possible to achieve a battery pack capacity rating of 68Ah ... if each 18650 cell capacity rating was 3400mAh (20S20P = 68Ah). Is it possible to cram four hundred 18650 cells into that 72V (20S20P) 200 DAT.BIKE battery pack enclosure that's pictured below ...

What makes you think it's a 18650 battery pack? Even if it were possible the cells are so close together making passive airflow cooling INEFFECTIVE! Furthermore each of the tightly packed 18650 cells may be wrapped in a fiber cushioning sleeve making even forced airflow cooling next to IMPOSSIBLE!

Are you 100% sure that 72V (20S) battery is rated at 68Ah? Are you 100% sure that battery uses 18650 cells?

Still there is the issue: if your cells are getting hot enough to need cooling, you're abusing them. Use more cells, or cells with a higher current rating.

Thank you for your reply.
you mean the best solution is control the power of battery system, right? instead of cooling it first ?

Yes and YES! ... being that passive air-cooling is NO solution and NOT necessary (Just My Opinion). That 200 DAT.BIKE was NOT designed for endurance performance racing, but rather for casual urban use (as you are well aware) with only intermittent peak performance like when passing, arriving at your destination on time, etc ... NOT for competitive endurance racing ... Xception being unlimited budget for buying replacement battery packs .

Me thinks the actual battery pack is 20S10P with capacity rating of 34Ah. It may be possible to cram two hundred 18650 cells into that enclosure ... thus the name 200 DAT.BIKE ... even so forced air-cooling is NOT practical.

Thank you for reply me !

First, about what type of battery. Actually I don't know what type exactly. I just know it's a Li-ion battery, and 1 image from manufacturer.

About quantity of cell, I think that orange case in the image can contain up to 400 cells. Because I see the dimension of 100 cells 18650 in this video. https://www.youtube.com/watch?v=nRQL_dOb2rU&ab_channel=K%C3%AAnhS%C3%A1ngT%E1%BA%A1o.COM
Also, dimension of Dat bike Weaver 200 battery pack you can see in youtube (estimate).

About battery cooling, I think you're right. Air-cooled in full of battery case may impossible.

And, the word "200" in its name is 200 km maximum distance / 1 charge, I think )

I'll thinking about it. Thank you so much.

 

[DogDipstick]

Actually, I'm working for graduation thesis in university. The topic is Air-cooled for battery (BTMS).

I want my thesis realistic, applicable, instead of just on paper.

So, the battery pack in image above is a battery pack of electric-bike company in my country.

I really need your answer!

Measure dissipate power and compare to volume.

The number will be in watts ( of dissapate power).

6w/Ah you do not need cooling.

Above 6w/Ah you need cooling.

Many OEM EV manufacturers will cool, either passive or active, air or fluid. Many here say if you stress you cells to make power and create heat you must be in need of greater quality cell..... this is not true. Many cells are made to output more while managing the dissipate. Cooling is an application. Used all over the EV manufacturer world.

A BTu is a standard measurement of heat amount. Heat transfer equation is complicated but very well enumerated in engineering.


Temperature is measured i degrees Kelvin.

 

[DogDipstick]

So, my question is: how can i do to cooling the battery pack while still anti dust, moisture, ...


Increase the mass, or the increase dissipate power. Dissipate can be increased with convection, conduction, or radiation.

Still there is the issue: if your cells are getting hot enough to need cooling, you're abusing them. Use more cells, or cells with a higher current rating.

well, the real answer is still that if you need to cool the battery, you are pushing it too hard and need a bigger battery, or a better one.

Many OEM manufacturers of battery systems disagree with you. MAny, many, many, many, many.

Honda, Kia, Hyundai, Chevrolet, Ford, VW, ect. Mercedes, Toyota, Tesla. NASA.

They all have active or passive systems to change the temperature of the cell during application. The cell would not survive without this cooling. OEM. Fluid, or semiconductor. Typical. Given climate range..( Sahara, Greenland, Space, Cincinnati. ).

And you still need to keep moisture from condensing inside.

The
Moisture does not condensate in a warm volume. I think the bigger problem is bringing the system inside from a cold enviromnet... to a warm one.

Yes, if you are blowing warm ( humid: by mass fraction) air on a cold thing, get, acquire condensation.

Blow cold (dry: by mass fraction) air on a warm item, get, acquire, no condensation.

https://www.goclward.com/wp-content/uploads/2015/01/Guide-to-Understanding-Condensation.pdf

"A bit off knowledge from a person who was taught, at an accredited engineering university, the process of atmospheric properties and their modification. A bit off knowledge from a person who became one of the engineering group that pioneered several aspects of thermal hydraulics evaluation as applicable to nuclear plant safety, later becoming an engineer with a senior engineer specialist designation for real engineering work, especially steam systems, the interactions of gaseous mixtures, the humidity of air, as well as several other gasses, combustion and heat transfer being this person’s specialty:

The amount of moisture (water vapor, or steam) that exists in ordinary air is generally expressed as “relative humidity, but relative to what?

It is “relative” to the maximum amount of water vapor that could possibly exist in the air, according to several variables, most generally the temperature of the air in question, although also dependent on several other conditions which we need not address as they are certainly not relevant to this discussion.

This maximum (100% relative humidity”) depends on the steam saturation pressure corresponding to the air temperature, the lower the air temperature, the lower the steam saturation pressure, and this by the laws of gas mixtures and partial pressures defines the upper limit of water vapor in this air/steam mixture.

In very cold air, say Christmas eve morning at 30F, the outside air can be, at most, holding about 22 grains of water vapor per pound of air, equal to a very small mass fraction of 0.3%.

Meanwhile, in the warm and comfortable country house, at 70F, the air in the house could hold as much as 110 grains of water vapor (1.6% mass fraction@100% humidity), about 5x as much as the cold outside air. For the inside house air to have as much moisture content as the outside air, then the inside house air would need to have a “relative humidity” of only 20%.


"ASHRAE Standards specify ideal comfort ranges of 68º to 74º at 40% to 60% relative humidity in the winter months."

-Frederick Rosse

OEM cooling regimes: Many are active or passive solution for use of cell. SEE: "Battery Temperature Management" column. Below.

These cells would not survive MTBF without temperature solution.

 

[Chalo]

These cells would not survive MTBF without temperature solution.

You're comparing a few pounds of battery in comparatively free air to literally tons of battery packed densely in sealed compartments. Also these manufacturers are choosing cells predicated on there being both heating and cooling for them. And they're drawing peak loads often in the hundreds of kilowatts.

None of what carmakers do demonstrates any need for battery cooling on an e-bike. If your e-bike needs battery cooling, it's because you're discharging at very high C rate (which the OP isn't).

 

[Hummina Shadeeba]

Labyrinth seal waterproofing


Why couldnt you use a maze shaped air inlet drilled with drain holes. The more complex the maze the better for water protection. I wonder if a complex maze would even reduce the air flow. Seems ideal for printing. Just a bunch of steep ramps in succession, maybe leading to wider chambers to release air pressure with drain holes going to the very bottom. Why not?