Re-Volt: Recharging a Legacy

Acknowledgements

• Project Advisor:
  • Dr. Yosef Allam
• Technical Advisors:
  • Dr. Christopher Coulston
  • Dr. Chuck Stone
  • Dr. Jeffrey Ackerman
  • Prof. Steve Richardson

Video

Elevator Pitch

We are a senior design team of 15 students who started in January of 2020 and have worked for a full year to convert a 1979 Volkswagen Transporter (“The Bus”) from gas power to electric power. The beloved bus was bought new off the lot in 1979 by the Sorbello family and has been like a family member since. The client is a fellow senior design teammate and eager for this opportunity to “recharge” this iconic family legacy. This unique design challenge will apply and expand students’ knowledge in a direction that is increasingly relevant to the automotive industry and consumer lifestyles for years to come.

While there are not many opportunities at Mines to learn about electric vehicle (EV) technology from the inside out, this project will prove to be an experiential platform on which students can build skills that are marketable and competitive. This project will challenge the student team to incorporate ambitious functional transformation while retaining the iconic vintage VW Bus aesthetic. A combination of off-the-shelf components and in-house manufactured items will allow the team to meet all conversion requirements. The target of this design challenge includes a 250+ mileage range and a minimum highway cruising speed of 70 mph, the solutions for which will be offered to the public as “open source” information on how to convert a vintage vehicle from gas to electric power. By making this EV conversion information publicly available, our team aims to promote the innovative work ongoing at Colorado School of Mines.

Design Approach

Design Solution

The stock, gas-powered engine has been replaced with an electric motor that is approximately twice the horsepower of the original engine. That motor mounts to the stock transaxle through the use of an adapter plate and shaft coupling, as well as an additional motor mount cradle that complements the stock motor mount. The motor, directed by the motor controller, converts the electric power from the high-voltage batteries into mechanical, driving power. The high-voltage battery pack is charged and monitored by a charger and battery management system. The stock user interface components are modified to accommodate the new powertrain of the bus. The Re-Volt team ensured the integrated system will work seamlessly with existing EV charging infrastructure; additionally, this conversion design will comply with all relevant laws and regulations, ensuring the clients will have no legal liabilities.

The new motor that was selected to power the bus is a NetGain HyPer 9. This motor was chosen because of the balance between its price and its impressive 98% efficiency. It produces more power and torque than the stock bus motor and has been used in previous conversions with the stock transmission. The HyperDrive X144 motor controller and motor have both been installed.

In an EV, perhaps the second most critical component behind the motor itself is the battery array. In addition to supplying the necessary power to drive the motor, the batteries also power auxiliary components such as interior lights, 12 V chargers, dash gauges, etc. The capacity of the pack is determined by the voltage and output ampere-hours of the total pack. The efficiency of the motor has a significant effect on range, as well. The conversion uses 18 Tesla Model S battery modules, configured with 6 packs in series, while each pack has 3 modules in parallel (3p6s). The resulting nominal voltage at full charge is 136.8 V.

After many long discussions with project advisors and companies like ZElectric and EVolve Electrics, the Dilithium Battery Management System (BMS) was chosen for this project. This system has the capability to manage parallel strings of many cells. The Dilithium BMS uses two units to control the charge levels: the BMS Controller (BMSC) and the BMS Satellite (BMSS). This will give the controller the expanded capacity needed to manage this specific combination of Tesla Model S battery modules.

For the onboard charger, the team selected the Elcon UHF 6.6 kW charger. There were a few reasons for choosing this over our intitial selection of the Elcon PFC5000. First, when attempting to order the PFC5000, it was discovered that this charger was soon going to be discontinued, and that the UHF 6.6 kW was the charger most similar to the PFC5000, but with modernized upgrades at no additional cost. Second, the benefits of switching to the UHF charger are that it is more efficient than the PFC, which will be a practical advantage for the clients. Third, it also works with the CANbus system that is being planned into our system. The price of the two chargers is comparable, making the more efficient UHF charger the best choice. 

The embedded system is necessary for the cooling system, cabin air heater, and user interface. The embedded system takes the form of multiple small, self-contained embedded systems (nodes). These nodes talk over a communications bus (CANBus is industry standard). We are using Serial/RS-232 due to unforeseen issues with embedded designs. Our current nodes include: user interface, heater, cooling, and temperature. Each node uses a PIC18F26K83 microcontroller. Communication protocol for the nodes prioritizes simplicity over versatility; this approach well suits the project deliverables, especially since the clients value simplicity. Code was tested using RobotFramework framework and Python backend.

The original accelerator pedal controlled the engine throttle with a cable; however, the electric motor controller requires an electronic signal to operate properly. To retain the original gas pedal in the cab, a simple cable-operated, HGM throttle position sensor has been selected to allow for seamless operation with the motor controller. 

The cooling system’s goal is to keep the batteries below their maximum normal operating temperature of 130°F, even at maximum power, allowing the bus to climb steep grades while loaded with gear, without de-rate. At the motor’s rated power, the cooling system needs to reject approximately 4600 W of heat from the batteries and about 300 W from the motor controller, totalling 4.92 kW. The radiator is a small dragster radiator with a 1400 cfm fan. The radiator is sized such that the cooling capacity will allow the bus to operate at full throttle continuously as long as the ambient temperature is below 103°F. At temperatures above 103°F, the motor controller will de-rate and reduce power consumption to allow the cooling system to keep up.

When equipped with a gas engine, the dash displays information that is pertinent to internal combustion. With a new, electric motor, the dash interface will be modified to provide the newly relevant data for EV usage. The small battery-monitoring display was purchased from EV West and allows the client to monitor the battery’s state of charge. LED indicator lights on the dash will be used for warnings similar to a check engine light on an ICE vehicle. This new battery monitor display was chosen due to how nicely it fits in the dash dimensions and the simplicity of the output display. The clients value the retention of a stock dash aesthetic.

Next Steps

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The final steps for this electric bus conversion will be working with the clients to develop a user manual that fits all of their needs and represents guidance required for safe and effective EV operation. This will include basic diagrams of all systems, charge instructions, which warning lights or key sounds to monitor, safety information for anyone working on the vehicle’s systems, and general guidance for safe operation.

In addition to a user manual, the team will be compiling the various reports, photos, and work log from the past year, providing them publicly online as open-source information. Open-sourcing the project has been a main goal since the project was presented to the team by the client. The goal will be to share what we have learned from component selection, physical conversion, and system integration with anyone looking to meet similar electric conversion goals. These resources will be shared on our website (revoltswagen.com).

Meet the Team