Some bright sparks
12 December 2012
John Lewis Partnership has introduced novel battery management from Enersys to control the energy used by its warehouse truck fleet at Magna Park The installation automatically manages battery allocation to ensure ba
The installation automatically manages battery allocation to ensure balanced utilisation, minimises energy consumption and prevents battery systems from drawing too much power when overall demand in the warehouse is above predetermined limits. This ensures other services are not disrupted and avoids the need for costly additional electrical infrastructure to keep the installation within budget.
The John Lewis Magna Park distribution centre covers around 800,000 sq ft with 50 warehouse trucks on site, including very narrow aisle combination pallet stacker/order pickers, reach trucks, ride-on pallet transporters, pedestrian powered pallet trucks, and electric counterbalance trucks.
One of the key considerations was the provision of change and charge facilities for the warehouse trucks. The warehouse works hard over extended shifts and the batteries need to support long intervals of up to eight hours between charging. The project team specified the highest capacity batteries available for the various warehouse trucks to help meet this objective. The traditional approach for an intensive operation like this is to select a spare battery for each truck so that one can be charged while the other is being used. In practice the number of spare batteries needed will depend on factors such as the recharge time and the frequency and number of changes.
Utilisation patterns at Magna Park predicted a 60 per cent spare battery capacity, in other words six spares for every ten trucks. The reduction in battery requirement has considerable benefits including lower capital costs and reduced space for the charging facilities.
Another consideration was the amount of power consumed. The electrical infrastructure for the building was finalised early in the design process and, while provision to the charging area was more than adequate, subsequent changes to meet evolving requirements of the operation meant that additional power supplies would be required. One estimate put the cost of providing this additional power supply to the charging area at around £100,000. Instead the project team looked at ways of limiting the amount of power consumed by the battery chargers without compromising the ability to maintain warehouse truck availability.
EnerSys recommended a novel implementation of its PowerNet battery and power management system to oversee all charging and changing operations. A typical PowerNet installation allows operators to manage their charging patterns to take advantage of off-peak rates for lower price electricity. However, as the system runs on a standard PC and is completely configurable in software, it can be set up with a wide range of userdefined parameters to provide a unique set of performance characteristics.
"We decided to manage our power requirements with PowerNet rather than with a costly upgrade to the infrastructure," says Ted Weager, operations manager MHE for the John Lewis Partnership.
Smart topping up Under normal operations all of the chargers can draw the power they need to top up the battery to which they are connected. However, if the available power is low the system automatically shuts down the chargers supplying the batteries requiring the greatest amount of charge.
Power is then allocated to the remaining batteries to ensure they are fully charged as soon as possible and ready when a truck requires a change. Batteries are brought back online for charging whenever power is available.
The batteries are charged with EnerSys Powertech HF chargers. They automatically detect the battery's level of discharge and will supply only the amount of power needed to restore full charge.
"The HF chargers are smaller and have a premium price but they save on electricity which helps us meet our sustainability goals," says Weager.
The 'intelligent' diagnostic software in the chargers transmits data via the system's PC to a large display screen installed in the changing area. The display clearly indicates the order in which batteries should be retrieved for each type of truck, ensuring only fully-charged units are taken. The system makes certain that all batteries receive the correct amount of charge before being used and that they are systematically rotated, overcoming the potential problem of operators simply taking the nearest available battery, regardless of its true state of charge. There is no longer any need to dedicate batteries to specific trucks.
The reach truck and pallet transporter batteries are arranged along one side of the facility on roller beds with the chargers mounted above for easy access and identification. Batteries are changed using an EnerSys Pro Series Tugger mounted on a modified powered pallet transporter.
When a truck enters the changing room the Tugger moves alongside and pulls the battery onto its own platform using a magnetic arm. The battery is taken to a free charging position and a fully charged unit, as indicated by the management system, is transferred to the awaiting truck.
"The operation is quick, efficient and requires no manual handling on the part of the operator," says Ted Weager.
Alongside the main battery bank is a smaller installation with one spare battery for the six VNA combination trucks.
These are normally charged using an inaisle system to minimise truck movements and reduce the time spent off-duty. The spare battery is used for periodic rotation to ensure balanced utilisation and as emergency back up.
"We wanted a system that provides us with data that we can use to monitor performance and make decisions about future requirements," concludes Weager.