Use diode to feed power from two sources

[Kiss4aFrog]

I have a 2007 Fleetwood motorhome with a LP detector. The old detector had two hots and a ground. One from the house batteries and another from the starting batteries. The replacement detector only has one red and one black lead. The instructions say to cap the starting battery lead and just use the lead from the house batteries. I like the idea of keeping both sources of power just in case something is left on and one of the two banks gets run down. I'd get an exact match detector but that company no longer exists. Can that be achieved by the use of two diodes connecting the two hots to the one lead of the replacement detector? If so what diode would you recommend?

MTI 30 series LP detector   https://www.mtiindustries.com/PDFs/rv/30_Series.pdf

[pigrew]

Yes, since it is somewhat low voltage DC, diode ORing them would work. The diode would reduce the voltage sightly (maybe by 0.5V), but the detector can operate down to 8V, so all would be well. I would use a pair of 1N4007.

The downside is that this does not give priority to one source or the other (the one with higher voltage will be discharged). You maybe be able to use multiple diodes in series on the secondary supply to reduce its voltage to be less than the primary supply voltage (as long as the result is at least the required 8V). More complicated circuits with transistors could be constructed to better control the priority.

A few uF (10uF 50V) capacitor wouldn't be a bad idea at the output of the diode circuit. Ceramic capacitors would be preferred since electrolytic can have issues with temperature extremes.