AC or DC

[MichaelGP3]

Will the OP be using normally closed contacts (I'm assuming that they are available on the model of CO detector being selected) keeping the interposing relay's coil energised during non-alarm conditions?

 

[ptonsparky]

How about just using a SSR at the starter? Current draw on them is almost nothing.

 

[MichaelGP3]

CO detectors are life safety devices. Shouldn't this circuit be incorporated into the building's fire alarm? As a standalone system, using N. O. contacts as stated in the original post: the devices, wiring, and the presence of control power (whether AC or DC) will not be supervised. Connected to a fire alarm input module or zone and using an end of line power supervision relay, or using addressable CO detectors all of the above is supervised. The standby battery 24 volt DC power from a fire alarm ensures occupants are warned of CO during power failures when the exhaust fan will be down if there is no emergency generator present.

But hey, as Dennis Miller would say......maybe I'm wrong.

 

[GeorgeB]

Voltage stability.

and lack of inrush issues on coils ... but they'll close slower on average ... but nearly always in the same time ...

One SWPS issue not raised is that some loads, my electrohydraulic proportional valves in particular, can draw high (maybe 2:1 range) loads for very brief times ... 0.1 to 10 ms in general. Some foldback supplies regard these instantaneous peaks as shorts and shut down ... for some large fraction of a second ... detect no short then come back on, only to do it again.

Linear supplies don't do this. Valves can frequently be adjusted to not present these loads. If a SWPS is used, the rules become something like ampacity of 1.5x the largest attached plus the rest ... ASSUMING as is good practice that they power up at no command.