I am no electrical guru but here is my response based on my 540 hours of RV-12 operating time: The ROTAX 912 ULS uses an integrated AC generator with an external rectifier-regulator (aka "dynamo") to produce electrical energy for both the ignition system and the 12 volt DC airframe system. This "dynamo" produces power in much the same way as the "generators" of yore (i.e., low RPM produces low electrical power). At lower RPMs, I typically see low system voltage and negative amps -- depending on the accessories (e.g., lights, AP, etc.) in use at the time. At high RPMs, all appears to work well with 13.9 volts and 1 amp consistently being displayed. I have given up on trying to correlate electrical system readings beyond that stated above -- the voltage and amp readings vary a bit at other than high RPM settings.
ps -- I now have 410 hours on my relocated Ducati regulator/rectifier -- fingers crossed!!
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 580+ hours (as of Dec 2017)!
through June 2018.