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      Power Supply FAQS

      Why did the power supply shut down during operation, and can it be restarted?

      There are two situations that will cause the power supply to shut down. The first is the activation of the over-load-protection feature (OLP). To address this situation, we recommend increasing the output power rating or modifying the OLP point. The second is the activation of over-temperature protection (OTP) when the internal temperature reaches a predetermined level. All these circumstances cause the power supply to enter protection mode and shut down. The power supply will return to normal once these conditions are removed.

      How to determine an efficient power supply?

      Modern power supplies are distinguished by ever-increasing efficiencies. Can customers, however, rely on the efficiency specifications listed in the manufacturer's datasheets? The following five recommendations should be given highest priority when measuring power supply efficiency and have proved to be indispensable in practice.

      • Use precision meters: If possible, power analysers or highly accurate watt meters
      • Ensure proper cabling when setting up the measurement and that you are measuring the correct voltage.
      • When taking AC measurements, always use an electronic AC source if available.
      • Avoid EMC interference from the device under test.
      • Consider temperature and time influences.

      What is the difference between MTBF and service life?

      The terms MTBF and service life are frequently confused or used interchangeably, in practice. However, these are different processes, and both are required to describe reliability. They all have one thing in common which is that higher temperatures make the values much worse.


      The MTBF (Mean Time Between Failure) specifies the statistical average of how frequently a unit fails. Even if all parties work hard to keep the number of failures as low as possible, it is unavoidable that an electronic product will fail at some point. The symbol for failure rate λ (Lambda) represents the frequency of failures. The MTBF is the reciprocal value of λ. λ specifies the number of failures per unit hour. In practice, specifications in MTBF are more common, presumably because the failure rate λ is given in 1/hour and is a smaller value (as is the “failure in time” specification; 1 fit = 10-9 failures per hour), whereas the MTBF uses the unit of hours. The failure rate expresses the number of failures to be expected when a certain number of units are operated for a given period of time. In practice, this is the specification of interest.

      Service Life

      The service life refers to the time after which the components are no longer usable due to wear and tear, not to statistical failures during normal operation. This specifies the number of years after which a power supply can no longer perform its specified service. Electrolytic capacitors are the most important components influencing power supply service lifetime. They contain liquid electrolyte, which is diffused over time by the component seal. The manufacturer defines the end of the service life when parameters such as capacity and internal resistance have degenerated by a specific amount from the start value. The service life of an electrolytic capacitor is thus determined by its type as well as its operating temperature. Every 10°C increase reduces service life by a factor of two.

      Why use power supplies in parallel?

      By connecting two or more power supply units of the same type in parallel, they share the supply of a system or machine. Collectively supplying power thus enables a higher total power.

      What types of parallel connection are there for power supplies and does PULS power supplies facilitate passive load sharing?

      In general, electrical power supplies that can be connected in parallel are divided into two categories: power supplies with and without load sharing. A balanced current distribution is not possible with power supplies that do not have load sharing. This can result in an overload and overheating of a power supply, which can lead to device failure. Load-sharing power supply units, on the other hand, ensure a balanced current distribution. This prevents one or more devices from overheating. There is a distinction here between active and passive load sharing. In active load sharing, connected control circuits ensure that the output voltages of the power supplies are precisely synchronized. However, this is a very complex problem that is prone to interference. If a completely balanced distribution is not required, passive load sharing can be used. The output voltages are set to be as congruent as possible in this case. Passive load sharing is dependable and affordable. This mode of operation is perfectly adequate for many systems and machines. As a result, PULS specializes in passive load sharing for the majority of power supply units with paralleling functionality.

      What does derating mean for power supplies? And when is it necessary?

      Derating is the reduction of output power based on environmental conditions. To protect electronic components and devices from high temperatures and prevent failures, derating is a recommended protective measure. Each power supply's power reduction is precisely specified. Several environmental conditions can raise the temperature of the power supply and thus pose a risk. High ambient temperatures, an installation altitude of more than 2,000 meters, and mounting orientations that deviate from the recommended installation are examples of these, where derating is necessary.

      Can the MEAN WELL power supply be used in the 45Hz - 440Hz frequency range? If yes, what’s the consequence?

      MEAN WELL's power supply can be used within this frequency range. But if the frequency is too low, the efficiency will also be lower.

      Can the MEAN WELL charger be used on Lithium or other types of batteries?

      All MEAN WELL chargers are programmed to work with lead-acid batteries. Customers can customize their charging curve for other products that can customize the charging curve (such as the ENC / NPB series) based on the charging and discharging characteristics of the batteries.

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