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Thread: External alternator kit from Rotec Aerosport

  1. #1
    Senior Member bbs428's Avatar
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    Default External alternator kit from Rotec Aerosport

    Received my external alternator from Rotec Aerosport.

    They applied a nice discount due to the strong dollar overseas. It's a one wire Alt. Nippon-Denso type, 45amp. It can be easily modified to an external regulator if you desire. I had to purchase the plastic excitation plug separately. Would have been nice to have been included. Wiring diagram on their web site is for Jabaru 2200 not 912ul. I also had to mark and drill the six propeller hub bolt holes in the aluminum pulley. Would have been nice if this was done at the factory. But it's all simple stuff, so nbd. Everything bolted up fine. All hardware was included.

    Been debating if I should keep the internal regulator or go with a more sophisticated external regulator. In my 40 year's experience, I have had only one regulator failure that destroyed the battery and that was an external ford regulator on a 1969 mustang. Since I have a backup Alt. it makes no sense to add weight and spend more $$

    One thing to note that unlike the Rotax external Alt. kit, this kit the aluminum pulley will push your propeller spacer out 5mm. So if your cowling is all measured and cut it might not work for you. I took my prop. spacer to a machine shop and took 5mm off the thick end so all ended up the same.

    I saved over a thousand dollars vs the Rotax kit, so the inconveniences were worth it to me. We shall see if the internal regulator holds up or not. Given the time and resources, I would make my own bracket and buy the Alt. separately. These Alternators are priced between $83.00 - $200.00 on the internet.
    B&C has a balanced, heavy-duty, 40-amp Alt. at a substantially higher price.

    235.jpg
    rotec5.jpg
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. Ernie Pyle

    Brett Butler
    Building: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  2. #2
    Senior Member Eric Page's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    Most true 1-wire alternators cannot be shut off remotely. Does the Rotec alternator kit offer external control of the field so it can be shut off by the pilot or by an overvoltage sensing circuit?
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  3. #3
    Senior Member bbs428's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    It has 3 wires - two 18ga. wires that plug into the back and the 14v 45-amp output cable. So, it's not a true one wire, sorry for the confusion.
    Of the two 18 ga wires that plug into the back, one is for an Alt. warning light, and one is for 12+ field. No overvoltage sensing circuit. You would have to purchase an external regulator. If my amp meter showed a failure and/or the Alt light was illuminated, I would pull the 5-amp field c/b and switch to the secondary stock internal alt. If all I had was the external alternator, I think I would opt for the better external regulator imho.

    The LR3D regulator controller from B&C offers more protection.
    07-06742.jpg

    LR3D-14 Alternator Controller/Regulator, 14V (Homebuilt) - B&C Specialty Products (bandc.com)
    Last edited by bbs428; 11-21-2022 at 01:08 PM.
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. Ernie Pyle

    Brett Butler
    Building: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  4. #4
    Senior Member Eric Page's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    OK, that's good info.

    Some internally regulated automotive alternators have a "field" connection too, but in many of them it's not really tied to the field winding; it's a control line from the car's computer to the internal regulator. In those units it works to turn the alternator on, but pulling it to ground will
    not turn the alternator off.

    I looked at the Rotec website but couldn't find any technical details. I was looking for the answers to two important questions:

    1. Does the "field" connection on their alternator allow its output to be turned OFF remotely?
    2. If so, is it connected to the alternator's actual field winding, or is it an ON/OFF control signal to the regulator?

    Regarding panel indicators, a low voltage warning light is definitely useful to the pilot. It tells you that the battery is not being charged and allows you to troubleshoot or load-shed and find the nearest runway.

    A high voltage warning light is difficult to implement (a severe overvoltage condition can destroy the sensing circuit) and of little value since the voltage rate-of-rise can be extremely fast -- much faster than the pilot's recognition and reaction time.


    An ammeter is also of little value, for several reasons:

    • Alternators are inherently current-limited by the physics of their design
    • Current from the battery is inherently limited by the total load of all installed equipment
    • Wiring is protected against excessive loads by fuses or circuit breakers
    • System load is constantly changing, making ammeter readings difficult to interpret
    • Detecting anomalies demands that the pilot monitor or at least frequently scan the ammeter

    Sensing battery voltage and including active notification of low volts is a more useful way to monitor charging system function.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  5. #5
    Senior Member bbs428's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    1. "Does the "field" connection on their alternator allow its output to be turned OFF remotely?"
    2. "If so, is it connected to the alternator's actual field winding, or is it an ON/OFF control signal to the regulator?"


    I have no idea. Did some fishing around and the consensus is that the Nippondenso alternators field goes to the windings but until you know for certain, you don't really know.
    Guess I'll just have to check it out after startup! Will post a reply when I have the results.

    Agreed about the ammeter. I'll use the G3x to monitor its output.

    Thanks for the insight, Eric!







    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. Ernie Pyle

    Brett Butler
    Building: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  6. #6
    Senior Member Eric Page's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    Quote Originally Posted by bbs428 View Post
    Guess I'll just have to check it out after startup! Will post a reply when I have the results.
    Yes, please do! The answers will be useful to anyone considering an external alternator.

    Unfortunately, on-engine testing can only answer question #1 if switching the "field" input turns the unit ON/OFF, but without asking Rotec or reverse engineering the unit, we can't answer #2.

    You may know all of the following -- if so, I apologize -- but let me try to explain why the answer to my second question is so important.

    1. If the "field" terminal is directly connected to one end of the field winding and the regulator controls the other end -or- if the "field" terminal supplies power to the regulator which controls both ends of the field winding, then an external switch, either manual or automatic, can shut down the alternator regardless of which component of the unit has failed.

    2. However, if one end of the field winding is connected to the "B" terminal and the other end is controlled by the regulator -or- the regulator is powered from the "B" terminal and controls both ends of the field winding, -and- in either case the "field" terminal is an ON/OFF signal to the regulator, then there are regulator failure modes (e.g. short circuit of the field drive transistor) that can cause the regulator to apply maximum field current with no way to turn it off.

    In paragraph 1, above, an external OVP circuit can trip the field breaker, ending the overvoltage event in a few tens of milliseconds.

    In paragraph 2, neither an OVP circuit nor pilot switch action can stop it. With a failed regulator applying full field current sourced from the "B" terminal and the alternator spinning, it becomes self-sustaining and stopping its rotation is the only way shut it off.

    Either of the examples in paragraph 1 is preferred, ideally with manual control of the field via a panel-mounted switch and an external OVP circuit. The examples in paragraph 2 aren't great choices for aircraft.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  7. #7

    Default Re: External alternator kit from Rotec Aerosport

    Thank you for sharing your experience with the Rotec Aerosport external alternator kit. It's great to hear that everything bolted up fine and that you were able to make the necessary modifications without too much difficulty.
    It's understandable to debate whether to keep the internal regulator or switch to an external regulator. As you mentioned, you have a backup alternator, so the risk of a regulator failure causing a complete electrical system failure is reduced. However, an external regulator can offer more precise voltage control and protection features such as overvoltage protection, which may be beneficial in certain situations.
    Regarding the propeller spacer issue, it's good to hear that you were able to find a solution by taking the spacer to a machine shop. It's important to ensure proper clearance between the cowling and the propeller to prevent any potential damage or interference.
    Overall, it sounds like the Rotec Aerosport external alternator kit was a good value for you, even with the minor inconveniences.

  8. #8
    Senior Member bbs428's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    Thought I'd follow up on the Rotec Alt kit.

    An issue arose when placing the ss7 top cowling on the plane. The bracket as is, allows the big lug of the alt. to be at the 12 o'clock position and in just outboard of the spinner fairing. There's just not enough room for the cowl to fit. You need at least .5 - .6 inch of clearance to clear the top cowl.
    Now there is enough material in the bracket to get it to work, but you have to really think out the geometry and have the proper tools to do the job. For the average builder it might be a bridge to far.
    I got it all to work nicely but it took the better part of the afternoon to do it.

    In the 1st pic you can see where it was hitting, just to the port side of the spinner fairing (the raised portion of the top cowl that mates with the spinner)
    2nd pic shows where it was hitting on the alt.

    Alt bracket interference.jpg IMG_1756.jpg


    I changed the position of the alt to index the lug to the 11 o'clock position. This also moved the alt. inboard which was great because we gained more clearance the further inboard we came. All this took a few hours of carving on a nicely anodized chunk of aluminum to get it all to work satisfactorily. Not a good way to go but the end result is it all works well, although it's not as pretty as before! Lol.

    IMG_1757.jpg

    There would be no issue for the round cowl.
    If you have the skill set - then buy the kabuto (Denso) 45 amp. alt. for $120.00, a gates belt for $25.00 and fabricate your own bracket. The bigger problem IMHO is the pulley, as it will have to be matched and machined to work correctly.

    I'll follow up again when I get the engine running and we can test the output and the voltage regulation.

    My recommendation if you need more alt. is to use the Rotax alt. kit - $$$$, But no issues.
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. Ernie Pyle

    Brett Butler
    Building: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  9. #9
    patrick.hvac's Avatar
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    Default Re: External alternator kit from Rotec Aerosport

    Thanks for the follow up. I was watching this with interest.
    🇨🇦CANADA
    Flying | SS7 | G3X | Edge 912

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