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Hi Rob and Michael or anyone else that may have had this issue,

This is a copy and paste. Any ideas on this?


" I need your advice on an electrical issue
(overcharging) that has plagued NXXXX on and off for maybe a couple of years
now but has made the airplane pretty much useless since July. I really
don't know if this is one underlying problem or several unrelated since we
replaced the rectifier and a melted connector once when it first happened.
The com radio smoked sometime after that and was sent to Garmin for repair.
This year I had intermittent overcharging indications that were just
occasional but in July would happen after warmup and half way downwind. Two
subsequent test flights after my tech worked on it went 1) no difference
(I.e. Started overcharging after warmup/runup and turn to downwind) and 2)
started happening as soon as I started the engine. This happened this past
Monday afternoon."

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

  • Re: Electrical Help

    by » 8 years ago


    There are several areas of failure that can cause an over voltage, in no particular order they are; An internal issue in the regulator where the regulator would fail to turn off. An issue in the control/sense circuit to the regulator (the C pin.) And a third could be caused by the dropping of the master relay, causing a disconnect of the battery.

    To test the first failure mode, disconnect the C pin when you have the over voltage condition. If the system continues to output power, the regulator is no good.

    The sense function of this pin turns off the regulator output, when the voltage exceeds 14 volts. To test the sense function we need to measure the voltage at the C pin when you have the over voltage condition. This voltage is referenced to ground. If the voltage is less than bus voltage, you have a resistive connection between the C pin and the bus. The regulator will never be satisfied because it thinks the system under voltage. If the over voltage is present at the C pin, and the regulator is still outputting, the resistive connection may be inside the regulator. Make sure the problem is not the Faston connector for the C pin as you meter lead is on the Faston, not the male pin.

    Should the master relay drop out, it will disconnect the battery from the charging system. The battery is integral to the changing system and will limit large voltage swings. To test this measure the battery voltage when your bus is over voltage. If the battery is not over voltage there is an open in the circuit.

  • Re: Electrical Help

    by » 8 years ago


    I would highly suspect that melted connector that was replaced; the melting indicates a poor connection (maybe it was the C pin). Poor connections in that big plastic multi-connector plug are quite common from what I hear. Many guys are replacing the big multi plug with individual Faston terminals that can be individually checked for tightness. A poor connection that overheats can easily trash the regulator.

  • Re: Electrical Help

    by » 8 years ago


    Melted plugs are not uncommon. This is typically blamed on the installation, but that is not always the case. There are some design choices that may accelerate this failure mode. This Faston connector is TE Connect PN 42281-2. The manufacturer recommends a maximum of 15 amps continuous. It's not a hard limit, they defer that to the product designer (Ducati) to determine. Next is the regulator plug. There is an issue in the plug design that does not allow the female Faston to completely mate with the male tab. It's about 20% short of the available mating surface area. A marginally rated connector, not fully seated is your starting point in this 20+ amp circuit. I'm not saying this won't work, but this is where you start.

    As for the OP's problem...my Garmin radio is rated 10-40 volts. The battery will damp the voltage in the changing system. For the system voltage to exceed 40 volts and damage the radio it is unlikely the battery was in the circuit...or maybe the radio failure is unrelated.

  • Re: Electrical Help

    by » 8 years ago


    Do we know what Aircraft/Engine/Alternator the problem is on?
    It may help to find a more specific answer.

    Generally, if you've seen one, you've seen them all, But ...

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


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