There are two distinct reasons to connect power supplies in parallel: Current Sharing and Redundancy. Combining of these reasons is common, and there are many ways to implement them. The unique considerations of paralleling deal mostly with the outputs of supplies, electrical and mechanical. The first step is to clearly identify the all of the objectives behind the intent to parallel.
The are several segments of the electronics industry that are often associated with power supplies used in parallel for power and redundancy. They are Telecommunications, Mass Storage, Storage Area Networks, Real Time Computers, and Public Safety Systems. Below are common terms used when discussing power supplies used in parallel:
Current Sharing: Refers to the division of the load among the supplies connected in parallel. The supplies will provide differing portions of the load by default unless measures are taken to balance the load. Current sharing is desirable for three reasons: (a) It increases the total amount of load current available. (b) It provides de-ration for the individual supplies, helping improve their potential long-term reliability. (c) It minimizes the potential for power bus glitches after a power supply has failed.
In many redundant power supply applications, the supplies are carefully selected and implemented to provide both redundancy and current sharing. Doing so provides fault tolerance and de-ration to improve the longevity of all of the supplies. Additionally, sharing of the load keeps all supplies ‘awake’ and conducting current. An idle power supply takes longer to come up to nominal output voltage. This could cause an unacceptable glitch on the power bus.
The goal of protecting a system from any single point of failure, in some systems multiple points of failure. The term can refer to simple paralleling or high tech power systems using redundant AC phases, Battery Back Up, N+1 hot swap power supplies, and remote, visual, and audible alarms. In the case of redundant AC phases, there are two power supply sections, or drawers, using separate AC phases. SPI has a great deal of experience designing fault tolerant power systems. Contact us directly to discuss a particular application. We can provide any pieces or all of the required power system hardware.