Battery Box Intake/Exhaust -- Clarification (April 1, 2014)

Question
1. Is an intake fan required on the main battery enclosure, or can just an exhaust fan be used?

2. Is an exhaust or intake fan on the supplemental battery box required?

Answer
In response to your first question an exhaust fan is required and an intake fan should not be used. The idea behind the rule was that sucking air from the box would help ensure that any battery outgassing would be directed through the exhaust (as opposed to blowing air into the box which could, in theory, go other places if the box isn't totally sealed).

As for the second question, the supplemental battery box now has to conform to the same requirements as the main battery box, so it would also need an exhaust fan. Attached for your reference are the relevant rules.


Related Rules

5.4.3 Battery Enclosure
The main battery pack must be fully contained in enclosures that can be sealed by event officials (thus sealing the batteries). A hasp latch for the battery enclosure will assist event officials in complying with this section of the rules. Battery Enclosure rules also apply to Supplemental Battery Enclosures.

(a) A battery enclosure is defined as a rigid box-like structure constructed from materials that are not easily flexible and that provides protection and stability to the battery system in the event of collision. Battery bags are not allowed.

(b) Batteries need to be strapped down, or held in place using structural members so that they will not move in the event of a vehicle roll over. If conductive materials are used to fasten batteries inside of the battery enclosure they must be properly insulated.

(c) The inside surfaces of battery enclosures made from conductive materials must be completely insulated.

(d) Battery boxes may not be used as dedicated crush zones as defined in Section 5.2.2.

(e) Other than forced air ventilation system intake and exhaust, the battery box must be air tight.

(f) Battery boxes must have forced-air ventilation which must operate whenever the battery system is electrically connected to the solar car, that maintains negative air-pressure within the box, cycles the air in the box 4 times per minute, and vents to the outside of the vehicle behind the driver’s compartment. [See diagram below]

(1) Scrutineering judges must be able to feel air being pulled into the battery box’s intake and out through the battery box’s exhaust.

(2) The battery box intake and exhaust must be clearly identifiable upon examination.

(3) There must be at least 3 cm of clearance between any devices inside the battery enclosure and both the intake and exhaust of the battery enclosure to ensure necessary room for air flow.

(g) Each battery and the battery box must be securely fastened to the vehicle’s structure so that the box will not move in the event of a crash. Nylon straps can be used to help secure the battery box; Velcro does not meet this requirement.

(h) Electrical cables must be properly sized to expected system currents.

5.4.4 Supplemental Batteries
All solar cars must be equipped with supplemental batteries to power solar car accessories, such as, but not limited to, radios, electronic speedometers, cameras, memory devices, computers (only if used for data gathering and not to control the vehicle systems), telemetry transmission, and battery box fans, and they must be totally isolated from the propulsion system of the solar car. Battery meters and monitors where the manufacturer recommends a direct connection with the propulsion system is exempted from being isolated. The main battery pack may not be used to power anything other than propulsion devices.

(a) Battery Type There are no regulations limiting the type, voltage, or weight of supplemental batteries.

(b) Low Battery Warning System - The supplemental batteries powering the following equipment: (1) lights; (2) horn; and (3) battery box air circulation fans, must be equipped with a low voltage warning system that will aggressively warn the driver with an audible alarm when the supplemental battery pack is getting low.

(c) Enclosure - Supplemental batteries must be enclosed in a battery box that is separate from the main battery pack. Supplemental Battery enclosures must comply to the same regulations as Main Battery Enclosures, described in Section 5.4.3.