When the going gets tough, power supplies get tougher. But what makes a power supply suitable for harsh environments? In this article, we’ll examine what it takes to make a tough supply.
Power Supplies for Harsh Environments
A power supply is an electrical device that provides power to one or more electric loads. It converts the electrical energy from the source to the corresponding current, voltage and frequency required by the load. Power supplies also protect the load by limiting the load current, shutting off the current in case of a fault, filtering electronic noise and providing power-factor correction. Power supplies have numerous applications, and they must be properly adapted to the application requirements.
Harsh environment refers to a setting in which device operation is difficult or even impossible. Most of the materials used in electronics are sensitive to certain similar environmental factors. In the case of power supplies, the most important factors that contribute to a harsh environment include temperature, dust, humidity, vibration and mechanical stress.
An example of a power supply designed for operation in harsh environments is the MEAN WELL HEP-1000 series. This series provides several features for environmental protection, and can operate as a power supply or battery charger.
Harsh environments include temperatures both extremely hot and extremely cold, so a harsh environment power supply must be designed to support a wide range of temperatures. The MEAN WELL HEP-1000, for example, can operate in environments with a working temperature from to + . The maximum power supply load depends on the ambient temperature. To select the proper power supply for the required operating temperature and corresponding load, system designers must check the derating curve of their power supply (see below).
A harsh environment power supply must also be protected against dust and moisture. To provide this protection, the power supply usually uses cooling by free air convection and fanless design. Using fully sealed aluminum casing with heat-conducted silicone gel provides protection for power supplies in dusty and humid environments. The HEP-1000 model optionally supports IP67 protection, in which the input and output connections are replaced by waterproof cables to protect the components from water. IP67 protection enables the power supply to be deposited in meter-deep water for up to half an hour. It simultaneously ensures dust resistance.
Vibration resistance is another important factor for power supplies designed for a harsh environment. The HEP-1000 series are fully supported and sealed, ensuring that internal components remain stabilized and connected in place. The HEP-1000 power supplies have been demonstrated to withstand a 10G vibration test.
Fanless Design: Cooling by Free Air Convection
When in operation, power supplies generate heat losses that could damage the components in the circuit if not properly dissipated. The most commonly used heat-conducting or cooling methods are natural airflow, forced air cooling, heat transfer through direct contact with a cooler component and liquid cooling systems.
Power supplies that operate in a harsh environment must be fully closed, so they typically employ a fanless design in which cooling is provided by free air convection. Fans are great for cooling power supplies quickly, but they have many undesirable characteristics when it comes to longevity and protection against harsh environments. They generate noise and tend to have a very high failure rate. By eliminating the fan, harsh environment power supplies resolve these issues.
Though eliminating the fan solves certain problems, it’s challenging to provide high output power with a fully encapsulated and fanless power supply design. The HEP-1000, for instance, is a high power 1000 W industrial AC/DC fanless power supply. Kai Li, project manager at MEAN WELL, explained how the company solved the design challenge.
“The unit is fully potted, so there are no air gaps between components inside the power supply. This enables better heat transfer, and the heat can be spread out more evenly throughout the power supply to the enclosure. The enclosure surface includes fins, like those found on heat sinks, to cool the power supply better. So it’s a combination of the potting compounds spreading the heat very evenly to the surface of the entire power supply and then the power supply surface being able to get rid of that heat,” Li said.
Dual Function: Power Supply and Battery Charger
Some applications, such as an uninterruptible power supply (UPS), require both power supplying and battery charging (e.g. powering a radio antenna and charging the battery). Instead of using two separate devices for each purpose, it is more convenient to use a single unit with a dual function, such as the HEP-1000 series.
There are three output voltage models in the HEP-1000 series: 24, 48, and 100 V. The output voltage can be adjusted with a built-in potentiometer. Power supplies must designed with the corresponding regulations and standards for safety, withstand voltage, isolation, EMC emission and immunity.
When operating in charging mode, the HEP-1000 provides four charging options: three predefined curves and one customizable curve. The predefined curves are designed for specific types of batteries, with 2/3 stage charging curves for different types of lead-acid (flooded, Gel and AGM) and Li-ion (lithium iron and lithium manganese) batteries. For the customizable charging curve, the system needs to be configurated with the recommended battery capacity provided by the battery manufacturer.
Charging curves have to be properly selected and adjusted for specific battery types. Overcharging or overheating can damage the battery and shorten its lifespan. Thus, it is necessary to detect when the full charge capacity is reached, as well as incoprorate over-temperature protection to prevent the battery from overheating during the charging process.
The HEP-1000 series provides a default curve which can be programmed via PMBus and CANBus. It allows enabling/disabling the charging curve, changing to a 2 or 3 stage curve, and selecting different curves commonly used for certain battery types. The default 2 (left) and 3 (right) stage charging curves are illustrated below.
The above charging curves are defined by using a hybrid charging approach that uses a combination of both constant current (CC) and constant voltage (CV) charging methods. The CC charging approach is used in the first battery charging stage. When the voltage reaches the maximum safe threshold value, the charging process continues by using the CV method. The real charging process is finished when the current levels off or when full battery capacity is reached. Stage 3 is the float operation mode where the voltage on the battery is maintained, which will provide the full battery charge condition without any damage.
Since proper charging is one of the most critical factors for a long and reliable battery lifespan, the HEP-1000 series has various protection mechanisms and temperature compensation functions. It measures the battery temperature by using a temperature sensor. If the battery temperature is increased, the power supply will decrease the charging voltage, thus providing the most suitable charging voltage to the battery under various temperature conditions.
Main Applications
Harsh environment power supplies like the HEP-1000 series are suitable for outdoor applications that are exposed to the elements, such as outdoor communication equipment. The HEP-1000 series is especially applicable for 5G deployments because of its power range and environmental protection. It is suitable for 5G microcells or smaller cell stations. These types of power supplies can also be used in robotic applications, such as for charging logistic, warehouse or lawnmower robots.
To learn more about the HEP-1000 Series, click here.