How to design effective power supply thermal management in industrial and medical systems
performance of the system fan(s) results in a lower (negative) pressure inside the chassis, thereby reducing PSU fan effectiveness. ■ The PSU fan(s) produce reverse airflow and the system fan(s) are helping the PSU cooling, not fighting it. However, if the air entering the PSU is coming from the system exhaust plenum, that can create issues that include a reduction in net airflow, as well as recirculation issues that cause the accumulation of heat in the PSU. ■ The air entry to the PSU is isolated from the main chassis airflow protecting the PSU fans from interference from the system fan(s). To realize the maximum benefit, the airflow channel for the PSU should have a low resistance.
of 24, 28, 36, or 48 volts direct current (VDC). For example, the ABC601-1T48 has a 48 VDC output. These PSUs are rated for 600 watts of continuous power or peak power up to 800 watts for up to 10 seconds at up to 60°C for the enclosed front-mounted fan models ( Figure 3 ). They have
a 5 VDC standby power output rated for 1.2 amperes (A) for U chassis models and 1.5 A for front-mounted fan models, and a 12 volt, 1 A, fan output. The ABC601 series comes in two packages, U-frame chassis or enclosed with a front-mounted
fan ( Figure 4 ). The ABC601 series features an internal current share circuit for parallel operation between units to enhance total power. The EOS Power VPS600 series of open frame PSUs from Bel Power Solutions feature a narrower input range of 85 to 264 V AC and deliver
A fan is not enough Many PSUs include a cooling fan. Rather than simplifying the thermal design, a PSU with a fan can complicate thermal design with considerations of airflow direction as well as the system or chassis airflow impedance and pressure. Complications include: ■ System fans can compete with and reduce the effectiveness of PSU fans, reducing airflow through the PSU. ■ The entry to the PSU fan can have an unexpectedly high impedance, reducing airflow through the PSU. ■ Cables or other obstacles can block the PSU airflow, reducing the effectiveness of the fans. There are several ways that system and PSU fans can interact, examples are shown in Figure 2 below: ■ The PSU fan(s) produce normal airflow, but the higher
Peak vs. nominal power rating and derating Derating is often different for peak power versus nominal power. Peak power needs vary widely from a few milliseconds (ms) up to 10 seconds or more, and it’s an important consideration in many industrial and medical systems. Consider two 600-watt PSU series optimized for different peak power delivery; the ABC601 series of industrial and medical AC-DC power supplies from Bel Power Solutions that is rated for 10 seconds of peak power delivery, and the VPS600 series that’s rated for 1 ms of peak power. The ABC601 series provides up to 600 watts of regulated output power over an input voltage range from 85 to 305 volts alternating current (VAC) in single outputs
Figure 2: Thermal design must take into consideration the direction of airflow in the PSU and the relative strengths of the PSU and system fans. (Image source: Bel Power Solutions)
Figure 3: The enclosed front-mounted fan models of the ABC601 series deliver 600 watts of continuous power (red line on top graph) or up to 800 watts for up to 10 seconds (red line on bottom graph) at up to 60°C. (Image source: Bel Power Solutions)
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