When you say hoverboard, you think of Marty McFly, right? Or is that just showing my age … Back to the Future was (and still is) an iconic movie. Back in 1985 it seemed a futuristic, awesome dream to ride on a hoverboard. And now, in 2016, it is a reality. However, there has been a number of reports comprising users safety. Naturally these toys are popular and it has been reported that these toys (or more specifically their batteries) have a tendency to unexpectedly catch on fire in a range of situations. There have also been house fires reported that are allegedly due to the use of lithium ion batteries which leads us to the question of: What are the risks for storing these types of batteries at home?
Lithium batteries are very popular for many devices – especially where the weight is important as they are lightweight, compact & energy dense. This is the same chemistry that produces these qualities which also makes them very sensitive to environmental conditions such as:-
Temperature – if charged at very cold temps the lithium ions plate onto the surface of the anode. They then “grow” out of the surface of the anode having then the potential to form a conductive path to the cathode which causes an internal short circuit. At high temps, the internal composition of the cell breaks down resulting in uncontrollable chemical reactions which create more heat and increases the rate of reaction resulting in thermal runaway.
Overcharging & Over Discharging – Overcharging causes much the same reaction as charging at cold temps & also produces carbon dioxide gas at the cathode which increases pressure. Over-discharging is more hazardous as copper that is included in the anode dissolves when the cell reaches a low charge (normally controlled by the anode preventing this). When charge is restored to the battery, the copper becomes solid again & thus falls to the bottom of the cell creating a potential short circuit.
Battery Monitoring Systems (BMS) & Safety Features – A suitable BMS that monitors the voltage & temperature of cells will provide protection, however it does increase the product cost, so often manufacturers will monitor groups of parallel cells as an alternative.
Any of the failure examples above may be the reason behind the recent hoverboard fires and have been caused by substandard battery components, poorly designed BMS’s & non-compliant or faulty battery chargers.
Retailers & consumers should ensure that both the hoverboard & the charger are compliant with AS/NZS3820 (Essential safety requirements for Australia & New Zealand). The most expensive component of self-balancing hoverboards is by far the battery and therefore this component is the natural target for cost cutting measures. Such a fault would explain the boards that caught alight both during charging and while being used. All battery chemistries may fail if treated incorrectly. Therefore when using a battery type for mobile applications, it is obvious that quality batteries incorporating a suitable BMS provide reliability & performance.
Now you’ve got your safety covered – enjoy your hoverboard. (Just watch out for Biff!) ; )
Information sourced from NECA News publication March/April 2016.