As the team tries to pass exams during their breaks from Solar Car, team alumnus Steve Hechtman steps in as a guest author for this week’s Technical Thursday post.
Racing a solar-powered electric vehicle in competitions that span two continents and 3,000-4,000 miles of public roads presents a multitude of challenges for the University of Michigan Solar Car Team. One oft-overlooked challenge is near and dear to this team alumnus’s heart: waterproofing. The car does not need to stop racing in bad weather, because the car’s battery pack allows the car to drive up to 250 miles with no sun. This means that the rest of the car parts must be prepared to function in the rainiest, wettest conditions. There’s no room for error when it comes to waterproofing. If a critical electrical component were to fail because it was exposed to water, the team would have to pull over to replace the part. This would cost the team precious race time, and could mean compromising a victory.
Engineers go to great lengths during the design and construction phases to protect electronics and the driver from rain, dust, and dirt. Unlike the weatherproofing on a production vehicle, weatherproofing on the solar car must be done in a lightweight, efficient manner. The first level of protection is the outer shell of the vehicle itself. The painted carbon fiber surface of the car is not porous to water.
The solar cells are also protected. They’re laminated in a material that protects them from water and other elements. The seams between different solar cell modules within the solar array are filled with a thin layer of water-resistant silicone, which prevents water from getting under the cells and coming into contact with the wiring of the solar panels. A puddle of water has ions that conduct electricity; therefore, if water touches both the positive and negative connections of a solar panel, electricity tends to flow through the water, rather than into the batteries of the solar car. This would prevent the car from getting any power from that solar panel, and could also damage the panel itself. This accidental electrical connection is called a “short circuit.”
As discussed in a previous technical Thursday, the seam between the upper and lower halves of the car is sealed off from the elements with everyone’s favorite yellow tape. The driver door, however, is not taped, so the driver can exit the car unassisted just in case there’s an emergency. The door is one area in which weather-stripping or silicone may be used to prevent water from entering. Similar to a production vehicle’s door, a line of weather-stripping or silicone may be placed along the inside edge of the door. When the door is closed against the car’s body, this creates a weather-tight seal. Or, at least in theory it does. Some thoroughly soaked drivers would tend to disagree.
Aside from the seam on the door, there are only four other places on the car where water can enter: the three wheel wells, and the low-drag NACA duct in front of the canopy that provides air for the driver. The simple solution for the driver’s air duct is to have the driver close the vent during wet conditions, stopping the flow of all water, or at least making it more of a pleasant mist to make up for the lack of air conditioning. Although water is kicked up by the wheels, carbon fiber bulkheads are designed to isolate the wheels and suspensions from the remainder of the vehicle. Carbon fiber or nylon wheel well covers are also placed above the wheels to provide additional protection from the elements. This, however does not always stop the water as planned.
Even if the electronics are completely shielded from water, the rain may still be a nuisance for the driver. The driver usually expects to get somewhat wet during a rain storm, and hopefully holes drilled in the cockpit prevent water from pooling up and giving the driver a bath. Unfortunately, this is somewhat of a trial-and-error process.
But even in monsoon conditions, although the water may be able to soak the driver, it is not able to get to the car’s components. The 2009 Infinium team was soaked for a great deal of their testing in the Australian Outback, when water made its way through both the door seam and the wheel wells. In soggy times like these, a second layer of defense protects all electronics—each circuit board has its own enclosure to shelter it from the elements. These enclosures span a wide variety of construction, from custom-made Kevlar housings, to off-the-shelf lightweight plastic boxes, or everyone’s favorite, the Altoids tin that has housed both circuit boards and switches. Environmentally-sealed electrical connectors prevent water from entering the boxes where wires pass through. We work closely with sponsors like Molex to ensure that our connectors and cables are lightweight, easy to use, and protected from the elements.
Windshield wipers are impractical for weight, power, and aerodynamic reasons; therefore, a coating like Rain-X is applied to the windshield to keep it rain and fog free. In recent years, treadles tires have been banned from competition, as treaded tires provide more wet-weather traction while still maintaining low rolling resistance.
The best solution to keeping the car protected from water, of course, is to spend as little time driving in the rain as possible. Thanks to our team’s meteorologist, we can plan our race speeds so that we spend more time in the sun and less time going through stormy, wet weather!
Steve Hechtman is a 2009 Michigan Engineering graduate and 3-time solar car racing veteran. As a micro-electrical engineer and driver for Continuum in 2007 and 2008, Steve Hechtman had a vested interest in keeping both the car electronics and car driver dry. During the Infinium Project, Steve served as the Project Manager, switching his focus from electrical engineering to fund-raising and team management. During the 2009 World Solar Challenge, he led the team through the Outback as they competed in one of the most intense solar car races in recent memory, ultimately securing a close third-place finish.
Steve now works as an electrical engineer at the Johns Hopkins University Applied Physics Lab (APL) in Laurel, Maryland. From this remote location he undertook the colossal task of creating the new website and transferring all the information from the old Drupal website to this new WordPress one. He continues to advise the team in all things website and IT. In the future, he looks forward to traveling to Antarctica with APL to launch a giant balloon-mounted, solar-powered telescope into the stratosphere.