Hazardous environments consist of work areas that may experience elevated levels of corrosion, extreme temperature variations, high pressure, flammable substances, or explosive conditions. Devices operating on battery power need special design requirements to prevent the battery pack from becoming damaged due to these hazardous materials.
The operation of the battery cells should also not cause any negative reactions to occur in the hazardous area, such as a short circuit or increased temperature from the pack, which could spark a fire or explosion.
When designing a custom battery pack, the design of the device itself can provide many protections to the encased battery. However, battery cells should also obtain certain protections to its enclosure, venting capabilities, charging circuits, and protection monitoring to prevent excessive discharging, cell rupture, and damage from high temperatures. Battery packs must also go through certification through regulatory agencies.
Design Considerations
Battery cells will gain many protections from the design considerations placed into manufacturing the product itself. Many manufacturers will follow the ATEX and IECEx standards and provide IP ratings that tell users about the amount of corrosion resistance, moisture resistance, and shielding for dust that the device has. The battery enclosure itself will also provide shielding at an optimal level to address those factors. However, extreme external temperatures and how the battery cells vent gases are two vital aspects about battery protection for hazardous environments.
Custom battery pack enclosure design for hazardous environments being sealed in ultrasonic welder.
Extreme Temperatures
Applications may be used in places that have extreme high or extremely low temperatures. Cell chemistries can have their performance and capacity impacted by these temperatures. In the case of lithium-ion batteries, they operate at a temperature range from 32°F to 140°F. They should be protected in temperatures below freezing as lithium must be warmed before charging in these low temperatures. In many cases, switching to another battery chemistry, such as nickel-metal hydride (NiMh), nickel-cadmium (NiCd), or lead acid battery cells, may be desired.
The same factors hold true for extremely high temperatures. Both nickel-based and lithium-based batteries can be charged at a maximum temperature of 113°F and can safely discharge at temperatures of 149°F and 140°F, respectively, as lead acid can charge and discharge at 122°F. Charging or discharging at higher temperatures may require extra shielding to be applied to the battery cell enclosure or the device itself, or selecting a battery chemistry that can withstand such temperatures in the hazardous place.
Gas Venting
Some battery cells may need to vent safely to prevent the battery from swelling or erupting. If an enclosure is designed to allow the buildup of gas to escape, this dangerous gas could negatively interact with the exterior hazardous environment, which could lead to possible explosion, fire, or further damage to the other battery cells or to the device.
Careful design considerations must be taken to allow the gases to vent in a safe manner without having them built up in the battery or the enclosure. Selecting valve-regulated cells or sealed cells may be desired to prevent gas pressure build up.
Circuitry Protection
In addition to the battery cell itself, the printed circuit board , charging circuitry, and monitoring circuitry should also be protected. Design considerations will vary based on the circuitry that is used with the battery and the conditions of the hazardous environment. In many cases, potting and encapsulation are methods to employ to offer circuitry protection. Potting and encapsulation involves placing a compound, such as resins, to either embed the enclosure into a mold or to impregnate the electronic assembly with the compound. Both methods are designed to create a seal that is resistant to chemicals, corrosive agents, solvents, and moisture.
IECEx and ATEX Certifications
There are many national regulations that cover the use of devices in hazardous workplaces and explosive conditions. Two that are often talked about are the European Union's Atmospheres Explosives regulation (EU ATEX) and International Electrotechnical Commission's Ex certification system (IECEx). The regulations cover both the device and the components within the device, which include the battery cells.
The IECEx certification system is a global framework that sets international standards for regulators, manufacturers, and users to create and maintain safety in hazardous locations. It also covers repair facilities along with equipment. The EU ATEX certification falls under the IECEx certification system.
The ATEX regulations focus on regulating non-electrical and electrical equipment that is used in explosive atmospheres in the EU. The regulation has two directives as one directive (ATEX 114 Directive 2014/34/EU) covers the equipment used in these hazardous environments and the other one provides minimum requirements to protect workers in these same environments.
ATEX 114 directive applies to all equipment used in a hazardous environment including protective systems such as IoT monitoring systems and telemetry systems. For battery cells, they must be compliant or have received IECEx certification for use in hazardous places. The batteries may also have to meet other IEC standards.
ATEX regulations are only applied to batteries used in the EU market. In the United States, several different regulatory bodies have standards regarding the design, manufacturing, and the use of equipment in hazardous zones. The National Fire Protection Association has the National Electrical Code, which would be an equivalent system to the EU’s ATEX. Other organizations include the Occupational Health and Safety Administration, American National Standards Institution, and the Mine Safety and Health Administration (MSHA), and UL.
Summary
Battery pack protections against harmful environments will focus on shielding the battery pack from exterior dangers while preventing cell pressure ruptures. The type of protection that is implemented will be based on the hazards that will be faced when the batteries are in operation, when charging, or during storage.
Choosing a battery chemistry that can charge and discharge safely in these conditions and can withstand certain extreme external temperatures is one factor to consider. You may also take into design consideration how the battery enclosure can withstand exterior temperatures and how it will vent. Lastly, protecting connecting circuitry from these same hazards with encapsulation and potting can ensure that the battery pack will operate at the desired capacity.
