Active Workpage, so everything is still being worked through. Just a useful reference for anyone to see where the progress is. For updated information on everything ask Battery Box for access to Battery Box TrelloThe Enclosure is where our battery pack is contained and is also the most mechanically focused project currently in Battery Box.
Main Tasks for Fall 2023:
Fan Selection and Cooling
Adhesive Selection
Board Mount
Things Happening Soon:
Fan testing with wind tunnel
Talking to Micah
Fan Selection and Cooling:
Purpose:
Cells generate heat while in use due to internal resistance. We want to remove heat from the battery box to prevent overheating of the cells, which can cause thermal runover and damage our modules.
We are interested in comparing the 120mmx120mm fans to the 80mmx80mm fans to check if 80mmx80mm fans are able to provide enough airflow, but also to check if air will mostly pass over the modules in a 120mmx120mm set up. As a result, we may want to put a wall or something above the modules in the 80mmx80mm test so that the anemometer only takes the airflow from the air going through the actual modules.
Basics Background Information (more or less):
The PQ Curve is a characteristic of the fan. It shows the relationship between the airflow that the fan provides (in units of CFM or cubic feet/minute) and the static pressure is how much air pressure the fan creates in the system, intuitively we can see it as how “hard” the fan “pushes” the air.
There is another line/curve that is the Load Curve, also called the System Impedance Curve, or the System Characteristic Curve. It is a characteristic of the system where air is flowing. So our battery box with 9 modules would produce some Load Curve, and another box with only 2 modules would also produce some Load Curve.
The intersection point between the Load Curve and the PQ Curve provides the “operating point” of the fan. That is, the actual airflow and static pressure of the fan in that system. Actually trying to figure out how a fan will act in a system without any testing is kind of impossible as a result. Any fan can technically give the load curve, but if you get the load curve with an absurdly different fan it might not be so applicable.
Why airflow - static pressure testing and not just straight up temperature testing? Because even if you get some graph of the temperature based on the airflow, you can’t really extrapolate that on to how much temperature will be removed with more modules because the airflow itself is going to change based on the added modules.
Our Task
We will be doing a wind tunnel test similar to what Micah did (Testing - Airflow Through Modules), except we will be testing different fan sizes, and just more fans in general. We will build our own cardboard wind tunnel for testing and evaluate the data that we get following a similar process to what Micah did here (Battery Pack Cooling).
List of Fans We Want to Test:
Noctua NF-F12 IPPC 3000 PWM 120mm https://noctua.at/en/nf-f12-industrialppc-3000-pwm
Noctua NF-A8 PWM 80mm $21.11 crid=223FQ9UUG3JJS&keywords=noctua+fans+80mm&qid=1688164914&sprefix=noctua+fans+80mm%2Caps%2C78&sr=8-4
PQ Curve:
View file name noctua_nf_a8_pwm_specs_en (1).pdf
Arctic Fan F8 PWM 80mm
PQ Curve: https://support.arctic.de/en/f8-pwm/docs
Phanteks 120mm ($34.99), outperformed Noctua 120mm fans: https://www.amazon.ca/Phanteks-PH-F120T30_BG_3P-Triple-Pack-high-Performance-Excellent/dp/B09B2LNFV4?tag=hardwar06-20&geniuslink=true
Noctua NF-A9 PWM 92mm https://noctua.at/en/nf-a9-pwm
PQ Curve:
View file name noctua_nf_a9_pwm_specs_en (1).pdf
Adhesive Selection (will update later, but epoxy is looking very nice)
Board Mount (will update)
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Finish Prototyping
Board Mount
Wire Harnessing
Make Final Product
Design Requirements
The design of the enclosure is based on the following requirements:
ASC Regulations
Impounding with seals (max 4)
Safety
Battery pack cooling (prevent overheating)
Ease of removability
Size (must fit in chassis)
Weight (minimize)
Most of the requirements are pretty straight forward, we need cooling because overheating batteries can cause thermal runaway, which is when the batteries enter a sort of amplifying feedback loop where: battery gets too hot → becomes more resistive because it is too hot → becomes hotter because of increased resistance → gets hotter → becomes more resistive because it is too hot → becomes hotter because of increased resistance → …keeps repeating until it bursts into flames and our car is gone.
We need to consider the ease of removability because we might have to take the box out to make changes to the modules or fix something inside of it. For example, if a single cell in a module becomes non-functional, we have to replace the entire module.
Size and weight are important constraints because we need to make sure our box actually fits into the space that the chassis provides, and it also needs to be as light as we can make it so that the weight of the box doesn’t mess with the center of mass of the car and also because more weight → more energy needed to move the car.
ASC regulations is more than just impounding and safety but those were the main ones we kept in the back of our minds while designing. Safety is just to make sure our box doesn’t separate from the car due to a crash or a roll-over (though the design of the car and ASC regulations make it impossible for a roll-over to occur anyway). Impounding is a rule that makes it so that the batteries are not accessible from outside of the box. This rule is in place to prevent teams from secretly replacing their modules with fully charged ones or from secretly charging the batteries from an external source. The event gives 4 of these seals shown in Figure 2, which is used to “lock” the box and make it impossible to access without breaking the seals (which can only be done with permission from the organizers and will be monitored, probably).
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