Feature Batteries & Chargers
Rob Phillips, managing director of UK battery solutions provider Accutronics, guides design engineers through the process of embedding batteries in medical, military or automation applications
eliability and safety are the two vital elements that come to mind when looking at integrating a rechargeable battery into a pro- fessional application, especially into a mission critical medical or military device. However, that is far from the end of the story as there are a variety of other factors that need to be taken into consideration throughout the various stages of custom battery design. While many engineers believe that, as its power source, the battery is the very heart of the product, you could go even deeper into the core of the battery and argue that it is the cell that is the nucleus of the battery, determining the performance, lifecycle and durability of the application.
Smart batteries - a designer’s guide R
Because bespoke power sources are used everywhere from hospitals to manufacturing plants and military operations, it means there is no such thing as a typical battery design pro- ject. High energy capacity, low temper- ature performance, high availability, a longer lifecycle and specific battery size are just some of the things a cus- tomer may require. Therefore, finding out exactly what you want the battery to do for your piece of equipment is crucial to the success of the design.
Types available
There are a number of cell types avail- able to battery developers including Nickel Cadmium, Nickel-Metal Hydride, Lithium-ion and Lithium-ion Polymer. Due to their high energy den- sity and excellent safety record, the Lithium-ion chemistries have domi- nated product development in recent times. However, the older Nickel chemistries do still offer superior per- formance in certain applications. One fundamental guideline is to decide whether the battery has to with- stand extreme conditions such as freez- ing temperatures, scorching heats, humidity or dirt. In order to guarantee efficiency, Accutronics select only the type of cells that are suitable for these conditions. In these instances, the elec- tronics need to be programmed differ- ently to cope with the various environments, whilst the physical char- acteristics of the battery need to be robust enough for the given extremes. The ability to replace a cell if a supe-
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rior version becomes available will also help ensure the future availability of the battery. This guarantees a longer lifecy- cle for your battery and helps alleviate obsolescence related issues.
Design essentials
The physical characteristics of a battery, such as its size, durability and weight, also play a crucial part in its design. Similarly, performance characteristics such as efficiency, reliability and avail- ability are also essential. For instance, portable medical devices might require a high tolerance to vibration, so that they can be used while transporting patients by helicopter. Achieving this is a matter of managing the physical and performance characteristics simultane- ously, which is no mean feat. In military products, such as night vision goggles or rugged portable com- puters, which are often used in extreme environmental surroundings, the battery needs to be able to cope with those conditions and also be small and lightweight for ease of car- riage. For instance, it might need to be watertight or feature a sufficient level of ingress protection to keep it secure against sand and dirt.
Material choice is central in ensur- ing these requirements are met. Magnesium for instance is very low weight, although expensive. If cost is a significant factor, which it very often is, a designer might instead work on the general shape and size of the bat- tery and insulation techniques to help meet the client’s expectations. Another important factor to con- sider, and one that applies to the inte-
APRIL 2012 Electrical Engineering
Above and below: the battery is the very heart of many military, medical and industrial electronic devices
gration of all sub-assembled compo- nents, is the availability of parts and their potential obsolescence. For this reason, engineers should avoid design- ing-in off the shelf consumer batteries. These can be poorly supported techni- cally and very likely to become obso- lete quickly. Simply choosing a customised industrial or professional battery, designed with your applica- tion in mind, guarantees you a lifetime of support.
Once a battery prototype has been developed, the final stage is to certify that product for use - from both safety and performance perspectives. Accutronics normally manages the entire approval process on behalf of its customers - each battery design under- goes the appropriate safety testing from, for example, the IEC (International Electrotechnical Commission), the UL (Underwriters Laboratories), as well as the IATA (International Air Transportation Authority) and military standards testing from MIL (The US Department of Defence Test Method Standard for Environmental Engineering Considerations and Laboratory Tests), if relevant.
Summary To come back to the original hypothe- ses, it becomes clear why the battery is the very heart of many military, med- ical and industrial electronic devices. We might also argue that it is the qual- ity of the design process which ensures the heart will continue to beat during the lifespan of the OEM’s device. As long as this happens and the battery provides power in an effi- cient and precisely monitored way, the device itself will do the rest.
Accutronics
www.accutronics.co.uk T: 01782 566 622
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