With the Location of the Battery Box Determined and the Layout of the Electrical Components

Objective:

With the location of the battery box determined and the layout of the electrical components within the box determined, the location and design parameters of the cooling devices must be determined to ensure proper airflow is created within the battery box. Things to determine include the location and size of fans and vents and the location and size for air intakes or ducts. Limitations include the location of the box and the amount of space left inside/outside of the box for cooling device mounting. Concepts proposed in this document are preliminary and are not final. No official analysis or simulation has been done to prove or disprove the effectiveness of these design concepts.

Scope:

1. Determine possible locations for air intakes/ducts
2. Determine possible locations for vents
3. Determine possible locations for fans
4. Determine possible locations for fan circuitry
5. Determine the sizes for these components

Battery Box Overview:

Figure 1 displays the battery box located in the vehicle’s frame. This is where the battery box will be mounted on the vehicle and the thermal management system design must work around this location. Figure 2 and Figure 3 display the contents of the battery box and where the electrical components will be mounted. Final wire routing is not shown in these figures and must be considered when designing the thermal management system for the battery box.

Figure 1: Battery Box Location within Vehicle Frame

Figure 2: Isometric View of the Battery Box and its Internal Components

Figure 3: Side View of Battery Box and its Internal Components

Air Intakes/Ducts:

Air Intakes/Ducts can be used to direct airflow into the battery box. Possible locations for air intakes or ducts include incorporating them into the body side panels or mounting one near the top of the main roll hoop. If they are located within the body side panels, the air would be directed into the sides of the battery box, where battery structures are located. If the air intake or duct is located near the top of the main roll hoop, the air would be directed into the top of the battery box, where the BMS and fuses are located. Figure 4 shows the possible locations for the air intakes/ducts. Figure 5 shows other performance vehicle teams and similar locations for their ducts.

Figure 4: Possible Locations to Incorporate Air Intakes/Ducts

Figure 5: Roll Hoop Location and Body Side Panel Location for Other Teams [1], [2]

Main Roll Hoop:

●Available Space

○The space near the roll hoop may be limited due to the location of Percy’s head (95th percentile male template that must fit within the vehicle per Formula Hybrid rules) and the location of the Tractive System Energized Light (TSEL), which must be mounted on the top of the roll hoop per the Formula Hybrid rules (see Rules section for list of rule). Figure 6 shows the current location of Percy’s head within the frame. The minimum distance from the top of his head to the bottom of the main roll hoop is called out to be 7.81”.
Figure 6: Distance between Percy’s Head & Main Roll Hoop

○The TSEL has not been finalized for the vehicle yet, but the specifications are known for the two options being considered. The TSEL used last year is shown in Figure 7 and is 3.8” tall. The TSEL being considered for this year is shown in Figure 8 and is 1.0” tall. The light is mounted onto a plate which then gets welded onto the main roll hoop. The plate on the vehicle last year was approximately 0.125” thick or less. The available space for an air intake/duct is listed below.

■Old TSEL: 3.885” available space

■New TSEL: 6.685” available space

○The available space with either TSEL should be sufficient to mount an air intake/duct. Though, this available space does impact the design parameters of the device.

Figure 7: Old TSEL Specifications

Figure 8: Possible New TSEL Specifications

●Mounting Options

○The air intake/duct can be mounted on the main roll hoop tubes using tabs. These tabs are located all over the vehicle for the mounting of various components and can be easily manufactured. The design of the air intake/duct must then include mounting holes or something similar in order to mount onto the tabs.

●Venting Options

○The top of the battery box would need to include a vent or similar device to allow the air from the intake/duct to enter the battery box.

○The component located in the middle of the top of the battery box is the BMS. Since this component is within the battery box, it has to comply to additional Formula Hybrid rules which can make venting in the top of the box difficult.

■In order to comply with Formula Hybrid rule EV2.3.4 (see Rules section for full rule), the battery box needs to be sectioned in a way so that any low voltage connections and isolated from the high voltage connections. This means that parts of the BMS must be enclosed within its own “box” that separates its connections from the rest of the battery box.

■If the vents are made in the section of the battery box which is enclosed from the rest of the box, no air will reach the battery cells. Vents either need to be located in a different section of the box or a different location for the air intake/duct should be considered.

○There are also components that will be mounted to the top of the battery box, which are currently not shown in the CAD model. This will, again, hinder the airflow into the battery box.

●Airflow

○As mentioned in the ‘Venting Options’ section, the airflow from the air intake/duct may very well end up in the enclosed section of the battery box where the BMS is located. This would result in no airflow reaching the battery cells, which is the MSD team’s main concern.

○If vents were to be located elsewhere on the top of the battery box, the airflow can enter the battery box. However, the air would come in contact with various other electrical components, such as fuses and wires, before it would reach battery cells. The battery cells are located under the components located at the top of the box. Therefore, the airflow that does reach the battery cells may not be sufficient enough to cool the batteries.

Body Side Panels:

●Available Space

○The air intakes/ducts would need to fit within the body panels or the body panels must be constructed in a way so that it acts as the air intake/duct.

●Mounting Options

○If the body panels are constructed in a way so that they act as the air intake/duct, the only consideration for mounting would be for the body panels. These mounting techniques are the responsibility of the Aerodynamic Subgroup on the Hot Wheelz team.

○If an air intake/duct needs to be mounted within the body work, then tabs can be utilized or direct mounting onto the body work can be utilized.

●Venting Options

○The sides of the battery box would need to include a vent or a similar device to allow the air from the air intake/duct to enter the battery box.

○The components located on the sides of the battery box are battery cells within their mechanical structure. This is ideal so that the first components that come into contact with the airflow are the batteries.

○The minimum amount of space between the battery cells and the side of the battery box is 1.73” and is shown in Figure 9. This allows for flexibility in vent design.
Figure 9: Minimum Spacing Between Cells & Battery Box

●Airflow

○As mentioned earlier, the air can enter through the sides of the battery box. The air intake/duct would have to be located near the bottom of the battery box, which is not ideal since only a few batteries may experience this airflow. Vent design should consider this to try and vent the air up into the box.

Vents:

●Pre-Made Vents

○If pre-made vents are to be utilized, appropriate space is needed within the box to mount these vents. Pre-made vents can be an option if the vents are to be located on the sides of the battery box because there is available space in those locations for mounting. The top of the battery box would not have the available space needed for mounting.

○The design of the vent is limited to what there is currently on the market. There may be little room for customization and it may be difficult to find vents for our specific needs and application. However, buying vents may save time during the build of the project.

○Waterproofing methods must be considered if sourcing pre-made vents. Sourcing vents with built in shrouds or other components/materials may be beneficial.

●Vent Slits

○Slits can be cut into the battery box where a vent is desired. It has been confirmed by the Electrical Mounting and Isolation Subgroup that manufacturing these slits is possible.

○The vent slits will have to be designed so that they pass the finger probe test outlined in the Formula Hybrid rules (see Rules section for more information). This restricts the width of the vent slits to less than the diameter of the probe used during inspection.

○Waterproofing methods must be considered. Team made shrouds or various materials should be considered to ensure water cannot enter the battery box.

Fans:

●Available Space

○If the sides of the battery box will be the source of the ducted air, then the available spaces for fans are displayed in Figure 10 and Figure 11, noted by the green boxes. These locations will force air over a majority of the upper batteries that the side vents will not access easily. Additional vents/vent slits may need to be added to the front of the battery box (the side closest to the driver’s back) to allow for the forced air from the fans to escape.
Figure 10: Left Side Battery Box Available Space for Fans

Figure 11: Right Side Battery Box Available Space for Fans

Proposed Preliminary Design:

Based on the location of the battery box within the vehicle and the location of the components within the battery box, the proposed design for the battery box cooling system is as described below.

●Vents will be located one each side of the box near the bottom of the box to allow air to be ducted into the box.

●Vents will be located on the front face of the box to allow for air to be exhausted out of the box.

●Ducting will be incorporated into the body side panels to force air into the sides of the battery box.

●Fans (minimum of 2, maximum of 4) will be located on the sides of the battery box near the rear.

Figure 12: Proposed Locations for Vents and Fans

Formula Hybrid Rules [3]:

●TSEL Rules

○EV9.1.1 The car must be equipped with a TSEL mounted under the highest point of the main roll hoop which must be lit and clearly visible any time the AIR coils are energized.

○EV9.1.3 It must not be possible for the drivers helmet to contact the TSEL.

○EV9.1.5 The TSEL must be clearly visible from every horizontal direction, even in very bright sunlight.

○EV9.1.6 The TSEL must be visible from a person standing up to 3m away from the TSEL itself. The person’s minimum eye height is 1.6m.

●Battery Box Sectioning Rule

○EV2.3.4 The accumulator container may not contain circuitry or components other than the accumulator itself and necessary supporting circuitry such as the AIRs, BMS, and pre-charge circuitry. Note 1: The purpose of this requirement is to allow work on other parts of the tractive system without opening the accumulator container and exposing (always-live) high voltage. Note 2: It is possible to meet this requirement by dividing a large box into an accumulator section and a non-accumulator section, with an insulating barrier between them. In this case, it must be possible to open the non-accumulator section while keeping the accumulator section closed, meeting the requirements of the “finger probe” test.

●Finger Probe Test Rule

○EV3.1.3 Finger Probe Test: Inspectors must not be able to touch any tractive system electrical connection using a 10cm long, 0.6cm diameter non-conductive test probe.

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