MGL Avionics User Forum

This is a similar question as the one @Rainier answered at (https://mglavionics.co.za/phpBB3/viewto ... 2016#p2016) but with a dual system and a particular problem.

The Revmaster has dual permanent magnet alternators. I have them wired with a 10K resistor from the AC line before the regulators to RPM1 & RPM2. Currently when RPM1-alternator is switched on, the RPM displays correctly. However when RPM2-alternator is switched on the RPM goes to '0'. The RPM needs to display with either or both alternators switched on. Both RPM1&2-alternators are wired in case an alternator failure, so that RPM can still show. I've tried many settings on the RDAC and verified wiring but the problem persists.

Is it correct that using dual RPM's (1&2) wired in this way will show the higher RPM of the two?

Do I even need the 10K resistors (what is the impedance of the RPM1&2 inputs?) or should I eliminate them.

The standard screen designs show RPM1.
You can customize the screen if you like - for your purpose you can use the RPM1<>RPM2 special text item - this displays RPM from either source that has the higher RPM. Note this is only available for the text readout. You could consider two graphic readouts on top of each other (one tied to RPM1 and the other to RPM2). In this case you will get two needles (if you choose an instrument with a needle). Normally the two should overlap and appear as one. If you do a mag check - one needle will show the RPM and the other will go to zero.