The Internet of Things has sparked a revolution where electronic systems add intelligence to applications ranging from smart cities to smart hotel locks and medical devices and more. This development is affecting coin-cell battery holders, where new versions include features such as easy-to-use snap-in designs.
The fundamentals of holder design include ensuring the holder meets basic usage and environmental requirements, that the supply chain is secure from poorly constructed counterfeit replacement parts, and that the end design is compliant with regulations governing battery replacement, especially for medical devices.
Shrinkage driving innovation
The IoT isn’t the only driver of battery holder innovation. Shrinking form factors also affect design. Take a hotel door lock for example. As they get smarter and use more electronics and communications technologies, one option is to run ac power to each door, through the frame and into the lock to power those electronics. A better option is to have instead a small, coin-cell battery-driven power supply that requires a battery replacement every six months or so.
Of course, the confined space means small holders, which is the general trend, especially for IoT. Other factors driving size and overall system cost down are Bluetooth, receivers, RFID tags, home automation, toll tags and bank security tokens.
As the number of integrated circuits in a design drops, it pushes the need for lower power, smaller batteries with the sweet spot moving from 1000 mAhr ten years ago to between 100 and 250 mAhr today.
Lower power needs have propelled innovation on the battery holder itself. While the basic materials still comprise high-quality thermally stable plastics and gold-overlaid nickel or nickel-plated steel, the holders themselves have become extremely thin. The original BH-800, developed 30 years ago, used a heavy metal contact to keep the battery in place.
With newer batteries, the plastic captures and the contacts are made as thin as possible, so the contacts move with the battery like flexible members. The plastic takes care of capturing the battery.
Along with making the design simpler to implement, the thinner contacts are free to respond more quickly to sudden jars or drops to avoid intermittent breaks in power delivery. They maintain better contact with the battery. A good example is the Snap Dragon holder.
The Snap Dragon is a design that involves a base piece and a snap-on cover. The battery goes on the cover. The user slides off the top, replaces the battery, and slides it back into place again. The plastic cover’s job is to keep the battery still while the contacts are free to move with the battery. That allows them to move rapidly to avoid getting an occasional break when jarred or bumped, such as when attached to a generator or a machine.
The danger of counterfeits
Some products, such as the BH-800 have been mass copied since their debut, and this practice continues for newer products. However, copying carries some danger as it is unlikely the counterfeit part has gone through accelerated environmental testing as well as shock and vibration.
Some products are made with poor-quality plastics. One instance, for example, involves a glucose meter. The holder didn’t maintain contact with the battery when the device was jarred, so the meter resets unexpectedly and gave inaccurate readings. In another instance, the plastic pieces of a baby thermometer came loose and became a choking hazard. Such cases abound, making a secure parts supply chain a critical part of successful design.
Ensuring battery holder and supply-chain quality
If you rely on a third party for their battery holders, check the product for:
–Documentation to show it’s gone through rigorous environmental and vibration testing, and in the case of medical devices, conforms to FDA CFR 21.
–Ensure that the holder has proper identification markings. “Gray market” devices, sometimes bought from online sources, generally have no markings and so are suspect.
–Perform a simple visual test. Excessive flashing or contact discoloration are big red flags. Flashing occurs when excess plastic extrudes through the mold and can prevent a battery from making contact. Contact discoloration hints at corrosion. If it’s gold, it should be bright gold: if it’s nickel, it should be highly polished.
–Pull on the contacts: if they don’t return to their original position, there’s something wrong.
If the contacts are twisted in any way, find another supplier.
Taking these basic measures can avoid millions of dollars in repairs where a full system may have to be stripped down and the holder replaced. While it’s tempting to look for legal recourse, if the source of the counterfeit part is China, there’s little to be done, so get it right the first time. You don’t want product recalls.
Memory Protection Devices
Filed Under: Design World articles, IoT • IIoT • internet of things • Industry 4.0