RV-12iS EMS and generator operation

[jrtens]

See the Rotax 912iS Heavy MM, chapter 24-20-00 which you can download from rotax-owner.com.

[thiggins]

https://www.rotax-owner.com/manuals/..._R3.pdf#page51

[subpar_bucker]

Thanks all!

[BobbyLucas]

I'm curious... Since generators can operate in 'reverse,' acting as motors and therefore as generator-starters, why does the engine have a conventional starter motor?

[Piper J3]

Rotax has alternator built into field-windings on back of engine case. Not the same as Tesla. My Prius however, doesn't have starter motor. Main drive motor (dynamic brake) back-drives the Internal Combustion Engine (ICE) to start it. ICE starts / stops dozens of times when driving....

[BobbyLucas]

So Lockwood just told me that they are dynamos feeding AC into combined rectifier/voltage regulators. But when I google dynamo it says they produce DC, not AC.

The article below says magnetos (AC), dynamos (DC), and alternators (AC) are all types of generators. If our engines are producing AC, then the conclusion is that they must use either magnetos or alternators. Lockwood said there are no commutators, which would mean they must be magnetos... My suspicion is that they are dynamos feeding DC to the rectifier-regulators, and the Lockwood tech just got that detail wrong. If that's the case, then why use a rectifier at all? To protect against reverse polarity?

https://www.linkedin.com/pulse/diffe...e_article_view

(Sorry if this is thread hijacking, but I hope it's pertinent)

[rcarsey]

Originally Posted by subpar_bucker

I have a dumb question prompted by a question I was asked by a friend: the 912iS engine's electrical system is powered by 2 generators correct? It sounds like it is possible to install external alternators if desired based upon this video:

Yes, See the Rotax Installation Manual, Chapter 24-00-00, Page 17. Page 33 has a schematic of how you'd integrate it with the rest of your aircraft. Its belt-driven and completely separate from the Fuse Box.. so you can think of it as an alternator in a traditional aircraft engine.

I think people use the terms generator and alternator a little loosely. See here for an explanation. Someone smarter than me will have to say if the Rotax internal "generators" are indeed true "generators". All I know is that they output AC and the external rectifiers mounted on the Fuse Box convert it to DC.

[h&jeuropa]

As rcarsey states, the terms get used loosely. This article attempts to explain the terms, https://en.wikipedia.org/wiki/Electric_generator

Rotax 912, 914 and 912iS use similar power generating systems. They consist of multiple stationary coils mounted to the engine and magnets mounted on the crankshaft that rotate within the coils. This produces AC voltage. The AC voltage is delivered to an external rectifier/regulator where it is converted to DC.

The coil assemblies are limited in the amount of current (amps) they can create and the rectifier/regulator is also limited in the amount of current (amps) it can produce/control.

The output of the coils varies with the rpm of the magnets past the coils, which is why a Rotax at idle produces very little electrical energy. It starts to produce significant energy above about 2500 rpm.

Hope this helps,

Jim Butcher

[BobbyLucas]

So much reading today, but very interesting and enlightening.

Here's my current understanding:

Generator: Any device that converts mechanical (or chemical) energy into electrical energy. https://en.wikipedia.org/wiki/Electric_generator

Dynamo: A generator that produces pulsing direct current through the use of a commutator. https://en.wikipedia.org/wiki/Dynamo

Alternator: A generator that produces alternating current. https://en.wikipedia.org/wiki/Alternator

Magneto: (permanent magnet synchronous generator) An alternator that uses rotating permanent magnets (ilo field coils). https://en.wikipedia.org/wiki/Magneto

So it seems to me that our engine uses internal magentos, which are a type of alternator, which in turn are a type of generator. So everyone is right! (Except the dynamo guy)

Yes, no? Certainly makes sense to me.

P.S. After Rob's post, I went and looked at the wires coming into the voltage regulator from the 'generator,' and there are three, so 3-phase AC, yeah?

[kshunz]

Originally Posted by jrtens

Welcome to VAF Scott. I think you will find that the 12iS is a great little airplane. Where is your flying club?

Thanks! It's the Boeing Employees Flying Association, in the Seattle area (Renton and Paine).