Redundant Power Supply Options for 24V DC Power
Ensure Steady 24V DC Power
For applications that require a steady 24V DC power source, even in the event of a power supply failure, a redundant power supply application can be used. The redundant power supply is basically a backup power supply in the event of a failure. The sizing of the redundant system should be sized in a way that the failure of one power supply will not drop out the 24V DC required to run the load.
Exploring Redundant Power Supply Examples
There is terminology to address this:
- 1+1 Redundancy – basically two identical power supplies that are in parallel with each other
- N+1 Redundancy – Using three or more identical power supplies.
You can see examples of both types below.
The power supplies should be isolated from each other. In the above redundant power supply examples, there is a redundancy module that the power supplies plug into, isolating them from each other. The benefit of using the redundancy module is you can use standard power supplies, preferably from the same family as the redundancy module. The power supplies should have a DC OK contact, so you will know when a power supply failure has occurred. Other things to consider are using separate fuses or protection for each power supply as well as connecting them to different phases or mains, if possible. Using a three-phase power supply will also give you the benefit of continued operation if you lose a phase.
The following will show redundancy examples using the Allen-Bradley® Bulletin 1606-XLE family of power supplies and redundancy modules. The same can also be done with the 1606-XLB and 1606-XLS families of products.
A New Redundant Power Supply Option
Allen-Bradley recently released a new power supply that has the decoupling MOSFET built in, so you don’t need a separate redundancy module. There are four part numbers that are available with this feature. Having the hot swappable plug connectors would be beneficial in the event of a power supply failure.
Below are wiring examples using the new power supplies that have the decoupling MOSFET built in.
In summary, we now have multiple ways to do a redundant power supply configuration, using either a separate redundancy module and standard power supplies, or special power supplies that have the redundancy feature built in.
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