This would be part of a pipe organ control system. Most of the organ components (e.g. air valves under pipes) are 12VDC. However, the solenoids to pull or push some items on or off can operate on either 12VDC or 24VDC. However, their design is such that they’re more efficient at 24VDC.
So how would one power the 24VDC solenoids with a 24VDC power supply, but control them with the 12VDC relay system which has its own 12VDC power supply which powers everything else in the organ?

 

Hello,

I see that you got a solution on AllAboutCircuits:
https://forum.allaboutcircuits.com/...g-12vdc-relay-separate-power-supplies.202488/

Bertus