SDN-C Redundancy Modules SolaHD SDN-C Redundancy (RED) Modules continually monitor the condition of two power supplies connected to a single load to support redundant power supply operation. If one power supply fails, the SDN-C Redundancy module automatically changes over to the other power supply. The MOSFET design of these modules generates less heat than traditional diode-based designs, translating to longer life of the components housed in the same enclosure as the redundancy module and a more compact design for the redundancy module itself.