Convert 24V to 12V @ 30mA
Using the 24 V I would like to trigger a relay that is built into another component, that has the specs of: 3 - 12 VDC, 3 - 30 mA.


This sounds awfully like a solid state relay input which is, basically, an infrared LED and series resistor.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. SSR with external current limiting resistor.

An infrared LED will drop about 1.4 V. If the SSR draws 30 mA at 12 V then the internal resistor is about \$ \frac {V}{I} = \frac {12 - 1.4}{30m} = 353 \ \Omega \$ (where 'm' is shorthand for milli).

Addition of an external 1.8 k&Omega; resistor would limit the current to about 10 mA at 24 V. This is well above the 3 mA minimum on-current.