Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

79 Batteries | Insight to get higher robustness and more accurate balancing between the cells, says van Giezen, as there is always a tiny difference between them. The BMS communicates with a remote app to give an online view of the battery’s status, and can be linked to the rest of an autonomous system via the popular CAN bus networking protocol. The BMS also implements another technique to lengthen the lifetime of the cells, called semi-active balancing, which only operates in the second half of charging and discharging when overheating can occur. All the charging is managed through the BMS, so a standard charger can be used – particularly important for military and unmanned applications as it means the systems can be lighter, says van Giezen. These packs are also certified for transportation, which is a big issue for global operators who want to ship unmanned systems around the world, he adds, and the first packs will be used in a commercial UAV and military systems in early 2016. Other materials Aluminium is another promising battery chemistry that is already being used in applications such as unmanned boats and electric cars, in the form of primary as well as rechargeable cells. The aluminium-air battery has one of the highest energy densities of any battery, up to 8 kWh/kg, but the technology is not used widely because of problems with high anode cost and removing the by-products (such as aluminium oxide) when using traditional electrolytes. This has restricted their use mainly to military applications; however, an unmanned electric vehicle with aluminium-air batteries has the potential for up to eight times the range available with a Li-ion battery, and with a far lower total weight. These primary cells are non- rechargeable as the aluminium anode is consumed by its reaction with atmospheric oxygen in a water-based electrolyte, and once the anode is used up the battery stops producing energy, leaving an aluminium oxide residue. Phinergy in the US has developed a proprietary process for the production of the anode that results in an increased use of energy while reducing unwanted chemical reactions such as the aluminium oxide to a minimum. The company has also developed a BMS for increasing the energy use of the battery. However, these are primary cells that are not recharged in the traditional way; instead the depleted aluminium anode is physically replaced, which the company says is quicker than recharging. Fast charging One way around the challenges of energy density is to reduce the charging time so that autonomous systems can quickly recharge themselves. To this end, researchers at Stanford University in the US have developed a different type of aluminium battery with a fast charging time that could offer an alternative to many commercial batteries now in use. “We have developed a rechargeable aluminium battery that may replace existing storage devices such as alkaline batteries, which are bad for the environment, and lithium-ion batteries, which occasionally burst into flames,” says Professor Hongjie Dai, who led the research. “Our new battery won’t catch fire, even if you drill through it.” This aluminium-ion battery consists of two electrodes: a positively charged anode made of aluminium and a Unmanned Systems Technology | Autumn 2015 The ExoMars Rover will be powered by a lithium-ion battery system designed to work in temperatures from -40 to +85 C (Courtesy of the European Space Agency) Cylindrical lithium-ion cells are tested and combined with a battery management system for UAVs (Courtesy of Cleantron)