Transformers and Power Supplies
Are diodes a good way to make power supplies redundant?
This has been an interesting conversation since the How to Make a 24VDC Power Supply into a Redundant System video.
This is a common question. There are pros and cons to all the different ways to set up a redundant power source.
Diodes
Pros
Cheap
Cons
Voltage drop of ~0.7Vdc
A good deal of heat loss with larger power supply systems
Manually have to balance voltage
Regular maintenance to check power source voltage drift
Mosfet Redundancy
Pros
70% more efficient than standard power diodes
Active load balancing (equal share of current from both power sources)
Cooler power supplies last longer
No need to balance power supplies during commissioning
Feedback on total system current
Feedback on status of redundancy and input voltage
Cons
“OR-ing” module can be a single point of failure
Because of the single point of failure concern, many process customers have opted to use 2 OR-ing modules and “cross-wire” the modules to maintain all of the benefits of the active redundancy while allowing the replacement of any single device.
Phoenix Contact has also introduced a single-channel OR-ing module known as the “S OR-ing” This module still has the advantage of the high efficiency and monitors with only the loss of the active load balancing.