Ducati Voltage Reg/rect Wiring

[Birdseyeview]

The wiring to all of the terminal connections on the regulator / rectifier seems fairly clear except for the "C" connection. Does anyone know what this is or what its purpose is? It appears that a 12VDC + line connects to the "R" and "B+" terminals and it may also connect to the "C" terminal as well. Schematics in my Rotax 912ULS manuals are cryptic at best when describing terminal functions and appear to include a small lamp of some kind connected across the "C" and adjacent "L" terminals. I don't plan to have any such lamp so I'm wondering if I need to wire anything to the "C" terminal. Any further insight on how to connect up to this "C" terminal (or not) is appreciated.

[jrevens]

Hi Larry,

The “C” terminal senses the voltage for control by the regulator. On my airplane I connected it to the same point (terminal on the electrolytic capacitor) as the wires from the “B” & “R” terminals. It doesn’t need to be a heavy wire - 22 ga is sufficient. You don’t need anything to the “L” terminal. I would highly recommend you take a look at the AeroElectric manual by Bob Nuckolls.

[Dave S]

Birdseye,

The "C" terminal must be connected to battery voltage as that is the controlling circuit on the system. If this is not connected, the alternator will be in uncontrolled voltage mode and fry the regulator/rectifier in very short order. Specifications call for no more than 0.2V difference between the "C" Terminal and the battery.

If a person looks at the schematic alone, it will leave a person with a lot of questions. Thoroughly review the section in the 912 series installation manual under "electrical system", "Technical data and connection of the electrical components", "Rectifier regulator", "Requirements for flawless operation of the rectifier-regulator". The text explains the function and proper connection of each wire.

A good starting point is to first decide what kind of cockpit indicator you want - idiot light, ammeter, voltmeter, ammeter/voltmeter and then go backwards - the problem with the schematic is that it shows wiring including all options. IMHO - the idiot light is worthless except for catching your attention (maybe) The ammeter is of limited value because it only tells you which way the current is flowing (to or from the battery). I went with a voltmeter because it will give a more comprehensive display of exactly what is happening with the system (over voltage, under voltage, proper normal operating voltage (should be around 14 v). The shunt is only needed with an ammeter. A voltmeter simply connects between the ground and bus. Deciding what indicator to have first permits a person to erase the un-needed connections.

Be careful with identifying the polarity of the capacitor too - those markings are quite cryptic on the capacitor too and a mis-step will cause an attention getting pop, smoke and a possible need for new shorts and a certain need of a new capacitor($).

I followed the above indicate rotax install procedures for our 912ULS and the system has worked flawlessly for 10 years sp far.

I don't have a photo of the connector - sorry.

[Birdseyeview]

Thanks guys, those are just the facts I needed. Thanks for the warnings as well. I've got a Westach V/A meter that seems to work fine for both voltage and amperage. I also just got a copy of the book John suggested, good stuff in there but I've just started to read it. I assume that hooking up the "C" terminal to some positive voltage controlled by the master switch is the right thing to do since the Rotax schematic stated the need to be able to break the circuit to the "C" terminal so as not to drain the battery after engine shutdown.

[Dave S]

Larry,

Exactly where I hooked in the "C" lead to the system I don't have a perfect remembrance of - I'll have to take a look next time I am out. I think I hooked it to the bus near the battery lug after the master solenoid so it is cut out when the master switch is off - BUT - I'll have to look:o

The book John suggested is great - between that and the Rotax installation manual - you'll get done:)

Enjoy your build

[jrevens]

Like Dave said, it should be connected somewhere on the other side of the master solenoid from the battery. As I mentioned, I connected mine right at the capacitor terminal (I have a capacitor that has screw terminals) that the wires from the "B" & "R" terminals on the regulator are connected also, since that is very close to the regulator in my airplane.

[Lawdog]

https://www.rotax-owner.com/en/?option=com_content&view=article&id=404&catid=22&Itemid=495

If you are logged in to Rotax Owner, see the above video as it explains the regulator wiring in detail

[Shadowrider]

Do you have to pay 30$ a year to view this video?

[Lawdog]

Yep, I think that’s the case but well worth it imo

[Shadowrider]

Thank you!