EV.4.3 Accumulator Container

F.10.1 Determines the general requirements of the Accumulator Container, which basically refers to allowable materials and specifications for the design as a whole. It must be made of non-flammable material and bonded by adhesive, both of which must be established at a designated temperature. Additionally, the container should be resistant to deceleration from all directions and documented thoroughly in the Structural Equivalency Spreadsheet (SES).

F.10.2 Determines the external structure requirements of the Accumulator Container, which is talking about all that you can see from the outside. It must have a floor/bottom, vertical wall, and cover/lid made from predefined material of designated thickness. It should also join walls to floors using either welding, fasteners, or bonding, and attach covers/lids with a defined ratio of fasteners to vertical walls per section.

F.10.3 Determines the internal structure requirements of the Accumulator Container, which is all that you can see from the inside. It must have internal walls which separate cells/segments and are at least the combined height of segments from floor to lid, and are properly fastened. Further, it must be sectioned by internal vertical walls which have a defined weight capacity, and be properly fastened. It should also allow each layer of segments a load path which does not intersect another layer if segments are vertically arranged, as well as secure and mount properly fastened segments which can withstand defined longitudinal, lateral, and vertical accelerations.

F.10.4 Determines the holes/openings requirements of the Accumulator Container, which refer to all of the perforations needed for ventilation, airflow, etc. The holes must be the minimum area necessary without interfering with at least 75% of coverage of each face of the segments, out of the driver's line of sight, as well as round (not slotted) and within range of a maximum diameter.

F.10.5 Determines the attachment requirements of the Accumulator Container, which are talking about how to mount the component to the chassis. must be documented thoroughly in the Structural Equivalency Spreadsheet (SES). Additionally, it must be critically fastened to the major structure of the chassis with the addition of backing plates, and be mechanically justified with either Load Based or Corner Attachments Analyses.

In order to charge the Accumulator at competition, it must be removed from the vehicle and placed on a team-designed Charging Cart. As a safety precaution, there is a designated charging area that is far away from the crowds of spectators and people. 

Because this is a mandatory part of competition, it is very important that every team is able to remove a self-contained Accumulator from their chassis, not only in one piece, but also in complete rules compliance for the safety of team members and others at competition.

Aside from inspection, where judges would need to open the lid to your Accumulator Container to verify rules compliance, the cover should remain closed as a safety precaution. Open, high voltage cables are most definitely a liability. In the case that a protective cover fails, the damage could be catastrophic.

F.10.4.1, similar to the preface of EV.4.3.4, allows for the internal or external walls of the Accumulator Container to be perforated as necessary. The only difference between these two rules this rule's mention of inside/outside walls.

F.10.4.2 stipulates that perforations made for the purpose of ventilation, cooling, wiring harness connections, or fastening be the minimum cross-sectional-area necessary. 

Therefore, tolerances for the openings that feed wires and cables should be minimal. Everything should be properly constrained without cutting into the shielded cable or giving excess wiggle room.

F.10.4.3 requires that at least three-quarters of every face of every segment are covered by internal and external walls. Not only should perforation diameter be kept to a minimum, but the number of openings should also not permit excess visibility of each cell from the outside or inside of the Accumulator Container.

This may seem intuitive, but here are some steps that can be taken to confirm compliance:

1. Draw a rectangle over the cell, calculate the area.

2. Locate hole patterns, calculate the combined area of every hole on that face.

3. Subtract the area of hole patterns from the area of your rectangle, and confirm that 75% of the rectangle's area is untouched.

This is a general rule-of-thumb for what the driver can see from a sitting-view, but can be conceptualized by drawing a triangle made of three points. The first is the driver's eyeline, connected to point offset downwards vertically by thirty inches, and then to a point offset horizontally twenty feet ahead of them and thirty inches below them. Everything encompassed by that shape is considered within the driver's line of sight.

This follows the same convention as F.10.4.4, but instead of referring to holes and openings, refers to pressure relief valves.

The pressure relief valve should not be directly visible to the driver, regardless of whether or not the firewall is installed. If something catastrophic were to occur and the pressure relief valve blew, we would want the driver to be as far from the impact as possible.

EV.4.3.8 is broken into multiple sections, each stipulating different regulations about the labels needed on the Accumulator Container.

EV.4.3.8.a requires that the school name (in our case, UNC Asheville) and the vehicle number (in our case, 225) be labeled on the Accumulator Container. 

EV.4.3.8.b requires that the "High Voltage Triangle" (pictured left) be visible on the Accumulator Container, and that each side of the triangle be at least one hundred millimeters (100 mm). EV.4.3.8.c requires that the container also is labeled with the "Always Energized" text (pictured left).

EV.4.3.8.d references T.9.1.1, and requires that if its conditions are met, the container is properly labeled "High Voltage".