What is a Traction Battery?
In the second in his interactive series Dr Mike explains what features are required to make 2V lead acid traction battery cells for fork lift trucks. He also gives valuable advice on how to choose the best fork lift truck battery for your particular requirements.
What is a traction battery?
According to European standard IEC 60254 – 1 lead acid traction batteries are used as power sources for electric propulsion in applications which include road vehicles, locomotives, industrial trucks and mechanical handling equipment. The batteries can be made of 2 volt cells, or 4, 6, 8 and 12V monoblocs (Fig.1). There is no stipulation on the internal construction of the traction batteries but the external dimensions are defined in standards such as IEC 60254 – 2. The capacity is measured over a defined discharge test from fully charged to 1.7 volts per cell over a period of 5 hours (C5 test).
Figure 1 Traction 2 volt cells and batteries for fork lift trucks
Traction Cell & Traction Battery
Traction batteries are comprised of both flooded and VRLA designs, in both 2 volt battery and monobloc constructions. In these designs the positive plates can be both flat plate and tubular designs. For the AGM variant of the VRLA construction, only flat plate versions are suitable due to the requirement of maintaining a uniform compression of the glass fibre mat used for the separator. Tubular battery with positive plate constructions generally give a higher cycle life than the flat plate designs. The tube construction (Fig 2) ensures that the positive active material is held firmly against the conducting lead alloy spine during the deep discharge cycles. The life of the traction battery is defined by the number of standard deep charge-discharge cycles which it can perform until it drops to 80% of the rated or nominal capacity.
The design of traction batteries is critical to providing a long and trouble-free operation in service. In order to achieve this, there are several key aspects of the cell or batteries’ construction which ensure that they are able to stand up to the demands of the cycle duty. The key components are the positive grid alloy, the active material chemistry and the method of separation and plate support. The deep discharge duty requires the battery to be recharged over a long period at a high voltage. This oxidises the positive spine which causes grid growth and eventual failure as the positive conductor becomes completely converted to PbO2. The alloy therefore should be corrosion resistant and also strong enough to resist creep growth. Microtex traction batteries use special alloys which have been developed over decades to give maximum corrosion and creep resistance for their tubular positive plates.
Similarly, other factors such as the active material structure and density are of vital importance in providing the capacity and cycle life required of lead acid traction batteries. The tubular positive plates are dry-filled with a unique lead oxide powder which again has been developed by Microtex over years of experience and laboratory testing. The processes also ensure that the correct, deep cycle form of lead dioxide (alpha PbO2) is formed in the positive tubes. Alongside this, the physical construction of the multitube and the internal support provide a space which collects material shed from the plates during battery cycling. This is important as capacity reduction and failure can occur from short circuit damage due to the shed active material creating a conducting bridge between the plates as the battery ages.
Figure 2 Construction of a 2V lead acid cell for forklift trucks
Features of a Traction 2v cell
Microtex offers Traction battery in Bolt on & Weld on designs
Microtex 2v Traction Cell