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Another Ducati Regulator Question

in 912 / 914 Technical Questions 7 years ago
In the continuing discussion of infamous the Ducati regulator-rectifier and the mystical writings that are handed down from Rotax, I noticed the following in the latest Rotax 914 Installation Manual:

"The performance specifications are given for optimal cooled
components. If necessary, use a separate heat sink for the
rectifier regulator."

Can anyone explain the "separate heat sink" concept?

When installing the RR for a UL Power engine, it was specified to use heat transfer compound on the metal back of the RR which was to be mounted to a large aluminum plate, thus facilitating heat transfer away from the RR through the back of the RR body. This would not work for a Ducati RR because the back of the RR is potting material that sits recessed from the regulator body. So I don't think that is what Rotax is trying to say.

And I don't think adding a fan is what Rotax is trying to say either, because if they were, I think they would simply say that.

What is the means of adding a "separate heat sink" as recommended by Rotax for added cooling of the RR?

  • Re: Another Ducati Regulator Question

    by » 7 years ago

    The VR heat comes from two sources. Internal and physical external heat. Usually the internal heat for most is normal, but that heat must be dissipated away from the VR Putting it in a hot spot within the engine compartment that may be hotter than most areas or it gets no air flow just adds to the heat problem.
    Vans RV12 folks have one of the highest VR failures in the industry because of where they mount it.
    If you can help it don't park it on a hot metal surface like a firewall that sits next to the exhaust. Don't cover it in a shroud like Vans does. (it slows heat dissipation). Don't park it right behind the exhaust (like Vans does on the #4 pipe). It's better not to put it in dead airspace in the instrument panel if it can be helped (Vans alternate mounting spot).
    A heat sink at times can be a separate piece of metal.
    If you can do park it where air flows freely and if you can make that cool air from outside the engine compartment all the better.
    That said most people have their VR's in the engine compartment and that in itself isn't an issue, but most try to keep them away from hot heat sources.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Another Ducati Regulator Question

    by » 7 years ago

    I tie-wrapped a computer muffin fan I had laying around to the VR in my under the instrument panel RV-12 mounting location. Previously too hot to touch, now I can hold my hand on it comfortably.
      
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  • Re: Another Ducati Regulator Question

    by » 7 years ago

    Thanks Roger and Tom. All good suggestions but what I'm really looking for is an answer as to what Rotax is talking about when they say in their Installation Manual:

    "The performance specifications are given for optimal cooled
    components. If necessary, use a separate heat sink for the
    rectifier regulator."

    How to "use a separate heat sink" is what I do not understand. I do understand that sometimes there are errors of translation, but in this instance that does not seem to be the case. They do not say "locate in a cool spot" or "add a fan for additional cooling." They specifically recommendation using "a separate heat sink." I cannot figure out how one would do this and would like to know what Rotax is telling us.
      
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  • Re: Another Ducati Regulator Question

    by » 7 years ago

    I don't know how a heat sink would work with this VR. IIRC, most of the bottom is that black potting material that probably won't transfer much heat and a relatively thin wall of metal that's all that would transfer heat to a heat sink.
      
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  • Re: Another Ducati Regulator Question

    by » 7 years ago

    I've put in a request for "separate heat sink" clarification to the factory - will report back here with the engineer's suggestions...
    Thank you said by: Ken Ryan
      
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