Battery Containment Charge Box
Electric motorised transport is mainly based around the use of lithium-ion batteries. These provide the required energy density at a cost and weight that earlier generations of batteries couldn’t. They are also finding their way into many portable tech applications and being rechargeable is driving down the cost of ownership and the need to replace them.
So far, so good, however, progress does often come with unintended consequences. As these batteries and their chargers become more widespread, the issue of them catching fire, usually during the charging process is coming to the fore. A quick online search of news sites shows that the issue is becoming more and more of a concern to those that have to deal with consequences, but it has not really made its way through into the public consciousness yet – perhaps this practical downside of going green does not fit the agenda.
In 2022 two SDS Group Australia suppliers collaborated to find a solution, it involved combining products, recourses and lots of material assessments, part of the testing process for our Detsafe range is to protect detonators from an external fire, such as that might happen as part of the vehicle accident. This requires that the Detsafes are exposed to at least 600°C for 30 minutes. The specialised XPT material used in the Detsafes is an excellent insulator and with some modification it could form the basis of a protective system for E-Bike batteries during the thermal runaway that takes place when things go wrong.
As a result of this collaboration and testing, the development of the first in the range of Charge Boxes came to fruition. The first model is sized for the most popular E-Bike battery and has been thoroughly tested to ensure it is a safe way to charge batteries and prevent the fires that are taking lives and destroying properties. Further models to cover the full range of lithium battery styles are immanent.
So who needs a Charge Box?
Many of the news stories about Lithium-ion battery fires relate to the private individual in their home. If you are bringing an item into your house, with such high energy density and an increasingly questionable safety record, you should consider the potential consequences. Much charging of these batteries is carried out at night, without active supervision. Letting a fire get hold in such circumstances can be avoided with the use of a Charge Box.
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Businesses can also benefit, in the push to net zero, many companies are encouraging their employees to commute using alternative methods other than by car. The proliferation of ‘Low Emission Zones’ is actively discouraging commuters from using their internal combustion based vehicles. The E-bike, and to a lesser extent the E-scooter, is becoming a more viable alternative.
As part of the core business of SDS Group, blast assessments are undertaken for existing and proposed facilities. For these it is now not unusual to feature a large bike racking area within the building itself, this can be for hundreds of bikes, often just one floor down from the main reception. How many of these will now be E-Bikes? How many of the owners intend to charge them at work? What happens when one catches fire in amongst so many others?
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Older facilities are usually less well configured for such centralised storage, maybe just some racks outside with public access. The E-Bike user will quite probably wish to remove the very expensive battery from their bike and bring it into the building – and might just intend to charge it up under their desk or somewhere else suitably convenient.
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The SDS Charge Box provides a means to deal with this issue, they can be kept in a planned location for use by staff when required. The Charge Box comes with the option to padlock it, so the user’s battery is secure. Utilising the cable port for access to the charging cable, it makes it possible to charge the battery inside the Charge Box making the surrounding environment safe and secure.
Hotel and hospitality establishments are catering for, or even providing E-Bikes for hire, the Charge Boxes are a distinct selling point for hotels. Is it best practice to have E-Bike batteries dispersed in guest’s rooms, charging up while they are out for dinner or asleep. It would be better that a designated location with a bank of charge boxes was made available, perhaps on a hire basis, so that the risk is managed and business continuity is maintained in the event of an incident.
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Lithium Battery Runaway demonstration
It was recognised at the outset that to test a containment system, it would be necessary to initiate thermal runaway on command, with the battery inside the box and without compromising the protection it offers.
Despite the range of battery styles for E-Bikes, scooters and even full sized cars, the majority of them use the same basic cell, stacked, packaged and ordered, according to the task at hand. This common denominator is the 18650 cell.
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Full sized batteries were not required or logical for just testing a means of initiation. It was concluded that eight, stacked in pairs, would be sufficient to see if initiation worked and then to see if propagation then took place to the unexposed batteries.
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A fully charged up, large capacity battery was prepared and the initiation system was fitted to the end that houses the charging port and lock. It was initiated and filmed with normal cameras and a separate thermal camera. The outcome was an education in just how energetic 18650 battery cells could be when they fired and it also reminded us of the of the old British ‘Fireworks Code’, although here it was adapted to ‘Never return to a lit battery’. The thermal camera measured temperature spikes of 750C.
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The next step was to encase a battery of the type used in the full scale propagation tests and see how the modified XPT blast mitigation material performed. Containing the flames, heat and energetic fragmentation in a small volume is always likely to accentuate the effects and even accelerate the burn. It had also been decided that we would let the smoke vent to avoid creating a pressure vessel which could just create an even bigger problem, as well driving up costs and complexity.
Three units with a steel frame construction, perforated steel faces and a bolted door were tested. The only significant change in variables was the XPT material thickness. What was the least amount of material that balanced the protection from flame and heat while allowing smoke to vent in a controlled way?
A small slot around the door was used to introduce the command wire for the initiation system – this same slot would be used for the charging cable in real world use.
We used thermocouple probes inside and outside the of the test boxes and a thermal camera attachment that could overlay the thermal image with the camera image.
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Our thinnest material option worked as hoped, boding well for a practical and cost effective solution. A bolt-on door however, is not a practical option. A simple but viable catch mechanism was required that would resist the repeated internal blasts. Tests with this build standard would then performed.
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We will shortly be adding to the range, with Charge Boxes designed to contain the longer but narrower batteries that are being integrated into bike frames and a wider Charge Box for the type mounted on the rear baggage rack.
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Away from specific battery containment products such as the Charge Box, the technology can be applied to areas such as barriers and/or other handling solutions for industry. Its all new, so please feel free to talk to us to solve these problems together.
Battey demonstration. Please do not attempt to open your Lithium Battery.
Inside the Charge Box after the battery runaway test.
Please contact SDS Group Australia for further information on Charge Box containment systems.