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I have the standard Rotax 912ULS setup with Ducati regulator/rectifier and 22,000uF capacitor. I’m having some issues with a small amount of smoke in the engine bay that briefly enters the cabin and then clears. More often is an electrical smell, very sporadically during flight. I have noticed it more often with higher RPMs during takeoff but also at intermittent times throughout flight. I've had several people look over the plane with no definitive diagnosis. Concerned that it might be the regulator rectifier, I ran some test with a voltmeter and used the following website as a guide: http://pointsforpilots.blogspot.com/2012/12/testing-rotax-912914-ge...
With the recorded values entered below, I’m suspicious there may be a wiring issue and that the regulator/rec is fine.
To start, I individually connected each terminal of the reg/rec, R, B+ and C, to the ground with volt meter and the master switch “on” but the engine off. Values were R 12.3V, B+ 12.3V and C 12.0V. Next, turned off the master switch essentially disconnecting the battery from the circuit but still had a voltage reading of 12.3V in R and B+ but not in C. This is where I’m concerned there is a wiring issues, unless the capacitor is playing a part here. So question is, should all three poles of the reg/rec have the same readings or are there other factors at work to explain this discrepancy?
Next, on to the regulator rectifier. With the same volt meter set up (reg/rec output to ground) and with the original output wiring still connected to the reg rectifier, I tested the voltage output of R, B+ and C with the engine running.
C: Seemed to function correctly. Engine running with alternator off and master switch off, output was 0. With alternator switched to on, voltage in high 13s/low 14s. When alternator switched off, voltage dropped to 0 and then master switch turned on, voltage climbed to 12s.
B+: Engine on, alt and master switch off. No voltage reading. Master switch turned on, no reading (would think this should be 12.3V from battery). Master switch turned off and alternator turned on. Voltage jumps to 17s but then slowly corrects to 14s. But then with engine still running and master and alt switched “ off, reading stays at 14.5V, similar to R. Any ideas on where this voltage is coming from?
R: Had some unexpected voltage readings that I can’t explain. With engine running, alternator off and master switch on, voltage was reading 37V (would think this should be 12.3V from battery). When master was then turned off, the voltage stayed at 37V. When the alternator was switched to “on”, voltage corrected to 13.9V; expected. But then with alt switched off, voltage stayed in 14s (plane meter dropped to 0). Not sure why. Any thoughts?
R and B+ had correct readings when the alternator was switched “on” with voltage in the 14s. Is this enough evidence to prove the rec/rectifier is functioning properly and that the awry values are likely from wiring issue/master switch issue.
Another argument for a correctly functioning reg/rec is that the electrical system seems to be charging the battery properly and the voltmeter in the plane shows accurate numbers. However, could the C terminal keep up the charge on the airplane for the most part, while the other poles may be causing the problem? I've heard the regulator is solid-state, either working or not (no middle road), but should there be the difference of each of the wires, as mentioned above?
Thanks in advance for the help! Art.