Saft batteries and EVM's battery management systems have proved a perfect partnership at a hi-tech car body manufacturing plant where they have been keeping a fleet of Automated Guided Vehicles (AGVs) working round the clock for over 10 years.
Saft, the world's leading designer and manufacturer of advanced technology batteries for industry, has worked for many years with EVM, the battery system specialist for automated guided vehicles (AGVs). EVM battery systems optimize the performance and reliability of the automated guided vehicles (AGVs) serving Daimler's Sindelfingen body pressing plant in Germany. The EVM battery management system (BMS) has successfully utilized the high cycling and opportunity charging capability of Saft's nickel-based rechargeable cells in EVM battery systems to keep the AGVs operating round the clock for over 10 years while extending the useful service life of the batteries by well over 60 percent.
The AGV system
The fleet of 94 AGVs at the Sindelfingen plant transport pressed parts, weighing up to two tonnes, from the press shop to the body shell manufacturing building via a high-bay warehouse over a route of 5.5 km. The first AGVs were commissioned in 2002 and the final roll out was completed in 2006. In 2010 a new Bluetooth communication and control system was implemented.
Each AGV is powered by an EVM onboard battery system that incorporates a 48 V Saft nickel-based battery with a storage capacity of 100 Ah. This supplies power for the drive, vehicle control system, electrical systems, electronics and sensors. Batteries based on Saft cells are more compact and lighter in weight than conventional batteries, and crucially they are capable of rapid and intermediate opportunity charging. This is critical for the plant's round the clock operations, since with some 6,000 journeys every day, there is no time for extended charging or battery changing. Nickel based cells thrive under this punishing regime that would be impossible for conventional batteries.
There are 35 chargers along the route with docking stations to ensure that the AGVs are always recharged before they start a journey. They can also dock briefly for around 20 to 40 seconds for an opportunity charge to top up while they are in operation.
The battery monitoring system (BMS 2010)
A key feature of the EVM systems is the battery monitoring system (BMS). It is adapted to the same size as a battery cell and is housed in the battery tray. It carries out vital tasks including measurement of battery voltage, charging current, battery capacity, number of full charges, water level and battery temperature.
The measurements made by the BMS and its responses are crucial in optimizing battery performance and extending its life. For example, if the battery voltage drops below a certain threshold, the host controller automatically sends the AGV to the charging station. The BMS also monitors the cell voltage and battery temperature by starting ventilation to avoid excessive gassing and needless water consumption, which could otherwise shorten the battery life.
The effective partnership between Saft and EVM illustrated by some remarkable figures. When the AGV system was first designed its business case was based on a battery life of four years. However, the plant maintenance team has found that it actually only needs to replace the batteries after seven years. In other words, while the capacity of an individual battery over its life was originally estimated at 300,000 Ah (equivalent to 3,000 times the nominal 100 Ah capacity) they are routinely achieving 500,000 Ah - an improvement of well over 60 percent.
'I have well over 20 years of working with Saft and in my experience their cells are the best in the business, for both product quality and the level of technical support provided by their local service team in Germany. So for this demanding AGV application there was simply no competition for Saft's technology,' said Walter Möller, General Manager of EVM. 'The effectiveness of the working partnership between Saft and EVM on this high profile project for Daimler is demonstrated by the exceptional performance and extended service life of the battery systems, which has vastly exceeded the initial expectations.'