The requirement for uninterrupted high reliability in communication systems is self-evident, and the power supply for communication systems, acting as the energy provider, is aptly compared to the heart of a human body. Complex power grid environments, such as overvoltage caused by improper operation of various electrical equipment or surges caused by lightning, are major threats to power supply reliability. So how can we address the increasingly prominent reliability issues of communication power supplies? Some have suggested DC parallel operation, but I believe the reliability increase will not be exponential, but rather between 0.1 and 2. An improperly chosen solution will result in a reliability difference between 0.1 and 1, while a properly chosen solution will result in a difference between 1 and 2. First, I want to thank the users who have already chosen our Schwitek power supplies for their trust in our products. I believe that the N+1 redundancy of the rectifier is more than sufficient for reliability. I also want to thank those users who are considering choosing our products; you have chosen to cooperate with a large international company with 15 years of professional experience in manufacturing communication power supplies. Therefore, I recommend that you only need one Schwitek power supply (here, one set refers to a monitoring device). The highly recommended optimal solution: Direct DC parallel operation of two power supplies with no capacity limitations. During operation, only one monitor controls the rectifier, while the other serves as backup. The monitor can be manually or automatically backed up. Since Schwitek power supply monitors have a relay indicating normal operation, manual backup is conveniently implemented, indicating monitor faults, and automatic backup is also easy to achieve. The key point of this solution is that the AC power supply circuits for both systems must be independent circuits. This is because the primary cause of system failure is surges such as lightning strikes or operational overvoltages in the AC power supply. Using two independent AC power circuits significantly reduces the probability of system failure. It also solves the problems of rectifier current sharing and battery charging current limiting after DC parallel operation. The disadvantage is that both systems must use Schwitek power supplies (SM40 or higher monitors). The second solution: DC parallel monitoring with hot backup. Basically the same as the first solution, except that the monitor must be an SC200, utilizing the SC200's master/backup function. While using the SC200 is more expensive, this can be considered an internationally advanced and perfect parallel operation. The control lines between the two systems are also fewer and cleaner. Third Option: Diode Parallel Operation Diode parallel operation is a traditional and relatively reliable solution, with no restrictions on the two systems. Disadvantages are: 1. Diodes have voltage drops, resulting in high energy consumption. 2. Capacity is limited; our maximum is 400A. See the diagram below for the principle. Fourth Option: Dual Parallel Operation System for Power Departments For power systems, the two systems operate independently under normal conditions. Only when one system's rectifier fails and there is a voltage difference of approximately 1V between the two systems does the two machines enter parallel operation mode. Manual operation requires extreme caution to prevent cross-charging between batteries. Parallel operation is only for emergency use; long-term use requires consideration of system current sharing and battery charging current limiting. (Note: In cases with one battery or only one power source having a battery, a pre-opening and then closing switch was used to ensure uninterrupted power supply during switching). See the diagram below for the principle. Fifth Option: Dual Parallel Operation System for the Military This solution has solved the battery charging current limiting function and eliminates the problem of battery cross-charging. However, the only unresolved issue is the current sharing problem between the two systems. Note that the two systems must be identical, which limits their application. See the diagram below for the principle. Conclusion Each solution has its advantages, disadvantages, and limitations. Some solutions only work if both systems are Schwitter products. Therefore, users can use a combination of solutions to leverage their strengths and mitigate their weaknesses based on actual needs. If the DC parallel system is complex to control and used improperly, it can be counterproductive and will not significantly improve system reliability. However, I believe the important principles for applying a dual-parallel system are: 1. The input circuits must be two completely different independent circuits with independent surge protection, and ideally, independent low-voltage transformers; 2. The control circuit should be simple, for example, the third solution is relatively simple; 3. The battery design should be placed as close to the load as possible to ensure load protection; 4. For applications in the power sector, due to the relatively good grid environment and standardized applications, N+1 redundancy of the rectifier is more than sufficient for reliability. This conclusion is based on years of experience repairing rectifier modules operating in the power sector.