Fast charging for buses is often done via an overhead pantograph, also known as J3105. But what are the pros and cons of the Pantograph Up or Pantograph Down versions?
Electric buses are becoming a mainstay in urban transit due to their efficiency and reduced environmental impact. A critical component of their operation is the charging technology, primarily involving pantograph systems. There are two predominant types: pantograph up, widely used in Europe, and pantograph down, common in the United States and Canada. This post explores the technical nuances, benefits, and drawbacks of each type to understand why one might be chosen over the other.
A pantograph is an apparatus mounted on the roof of an electric bus that connects to an overhead charging system. This connection facilitates the high-power transfer necessary to quickly charge the bus’s battery. The design and operation of pantographs are governed by international standards such as SAE J3105 (https://www.sae.org/standards/content/j3105_202305/) in the US.
Pantographs are favored in urban bus systems for several reasons:
• They enable a quick, automatic connection to the charging system.
• They support high power transfer, typically up to 600A, allowing for charging capacities around 450 kW.
The fast connection times and high power makes them essential for opportunity or layover charging, but are also often used on depots.
There are two principal types of pantograph, pantograph up, and pantograph down (also known as Inverted Pantograph, initially branded OppCharge).
• Pantograph Up: mounts the moving arm on the bus roof and it extends up towards a hood to connect.
• Pantograph Down: there are flat connection rails on the bus roof, and the charger pantograph is extended down towards the bus.
• Pantograph Up: The bus itself carries the mobile part of the charging mechanism. This can increase the vehicle’s height and total weight, however the extra roof height is often used for batteries or air conditioners anyway.
• Pantograph Down: The moving part is part of the charging station, located on a gantry above the bus. This design reduces the weight on the vehicle and minimizes vehicle height, offering better aerodynamics and potentially less stress on the bus structure.
• Pantograph Up: A malfunction affects only the individual bus, which can be replaced with a spare. The repairs can then be done back at the heated, safe and well equipped depot workshop. There are fewer cycles per pantograph for layover operation, leading to potentially lower maintenance costs.
• Pantograph Down: A failure in the charging station can disrupt service for any bus that uses that station, likely impacting a whole route. Repairs need to be done in the field, in any weather conditions, on an elevated platform.
• Pantograph Up: Generally involves less complex overhead infrastructure, potentially leading to lower initial investment and maintenance costs for infrastructure. The buses have more complex mechanisms.
• Pantograph Down: Requires more robust and expensive gantry structures to support the heavier pantograph mechanism. The components mounted on the bus are cheaper and simpler in Pantograph Down.
• Pantograph Up: Uses a straightforward wired communication identical to existing cable-based CSS DC charging systems. While it wouldn’t be standards compliant, it is electrically possible to make an adaptor from a CCS2 to a J3105 pantograph up hood. The pantograph actuator motor is on the bus and is directly controlled by the operator. Since the logic and communication components are also used for CCS2, the high component production volumes for other vehicle types will lead to low costs, readily available parts, and easy adaptations by charger manufacturers.
• Pantograph Down: Since the pantograph actuator motor is on the charger side, not the bus side, several steps are added as the bus needs to tell the charger to descend. The bus establishes a wifi connection to the charger (preferably secured) then signals the charger to lower the pantograph. Since several chargers could be nearby, the charger needs to be certain the bus below is the bus requesting the pantograph (and not a neighbouring bus), and it is properly positioned. It does this using a RFID positioning system with beacons on the bus. Once the Charger has confirmed the bus position and identity, it can lower the pantograph. These additional wifi and RFID communication components, and the associated controllers, add considerable complexity. The pantograph controller on the charger side is an added component compared to pantograph up. Since it is only used for buses, it will continue to be a low-volume specialist product. This will result in fewer charger manufacturers who can support pantograph down, and at higher electronics cost and complexity.
The choice between pantograph up and pantograph down configurations depends on various factors including the specific operational, maintenance, and charging strategy for a bus fleet. While the additional mechanical complexity on the bus is a downside for pantograph up, the advantages around maintenance location, isolating failures to a single vehicle, and avoiding the wifi and positioning systems can outweigh that. As fleets develop, compatibility with neighbouring systems, and vendor availability also become important factors. Transit authorities must weigh these factors to choose the most suitable system for their needs, taking into consideration the long-term operational efficiencies and potential technological advancements.
This is not intended as financial or technical advice and ChargeSim accepts no liability for actions taken based on it. Always consult a professional about your specific situation.