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Thread: Overvoltage Protection - how it works

  1. #1

    Default Overvoltage Protection - how it works

    Adding an overvoltage protection system is important with today's all-electric aircraft. An un-protected overvoltage condition could damage sensitive avionics, ignition systems, and other electrical devices on the aircraft.

    The most common overvoltage system today is know as a "crowbar" system, which shorts the alternator field wire to ground when an overvoltage condition is sensed. This pops the field circuit breaker and the alternator stops generating electricity.

    Vertical Power works in a similar fashion, albeit a bit more elegantly. It simply removes power from the alternator field wire when an OV condition is sensed. It also give you a voice alert in the headset. You can specify in the setup menus the trip voltage above which it will sense this condition. Typically 16v for a 14v system, and 32v for a 28v system. You can also specify a time frame - normal, or extended if you get nuisance trips.



    One of the reasons DO-160 specs call for electronics to run at 40v for 1 sec and 60v for 100 milliseconds is to withstand the short voltage spikes that may occur during an OV condition, as the voltage rises before the alternator is shut off.



    Above is a trace from the o-scope showing a test OV condition. The top line shows the bus voltage rising from 14v to 24 volts. Where it meets the first vertical dashed line is where it passes through 16 volts - the OV trip limit.

    The lower line is the alternator field power. You can see that it rises with the bus voltage, and approx 40 milliseconds (there are 1000 milliseconds in a second) later the Vertical Power system turns off the alternator field and the voltage drops to zero. Within this 40 ms period, the system has read the bus voltage three times to confirm it is an actual OV condition.

    Want insurance? A feature we'll implement soon is one that is not available for general aviation aircraft, maybe not even larger aircraft (don't know for sure). If the OV condition persists because the alternator has failed internally, the VP system will automatically shut off all the electronics to greatly reduce the chance of a runaway condition burning them up. All this happens within 1/10 of a second. If you were to do this manually, the avionics would likely be fried by the time you figured out what was going on (actual conditions may be different, your mileage may vary). If you're not comfortable with that, turn the feature off in the setup menus.

  2. #2

    Default

    Quote Originally Posted by Marc Ausman View Post
    Want insurance? A feature we'll implement soon is one that is not available for general aviation aircraft, maybe not even larger aircraft (don't know for sure). If the OV condition persists because the alternator has failed internally, the VP system will automatically shut off all the electronics to greatly reduce the chance of a runaway condition burning them up. All this happens within 1/10 of a second. If you were to do this manually, the avionics would likely be fried by the time you figured out what was going on (actual conditions may be different, your mileage may vary). If you're not comfortable with that, turn the feature off in the setup menus.
    This idea has not been implemented and we don't have plans to do so. Upon further thought, we've determined that the best strategy is to use an alternator that does not have this failure mode, such as an externally regulated alternator or a Plane Power. OV protection is built into VP products as well as most aviation-specific alternators or voltage regulators.

  3. #3
    Join Date
    Mar 2012
    Location
    Oshawa, Ontario, Canada
    Posts
    15

    Default

    What would cause an overvoltage warning on my D180 and not on the VP100?

    I had my first engine start rectntly and when i turned on the 1U switch for my Alt, the D180 gave me the warning and showed 19.6? I have a Planepower 70 amp alt with a LR-3C regulator.

    Thanks


    Don

  4. #4
    Join Date
    Mar 2012
    Location
    Oshawa, Ontario, Canada
    Posts
    15

    Default Disregard...

    Quote Originally Posted by DOnPatrick View Post
    What would cause an overvoltage warning on my D180 and not on the VP100?

    I had my first engine start rectntly and when i turned on the 1U switch for my Alt, the D180 gave me the warning and showed 19.6? I have a Planepower 70 amp alt with a LR-3C regulator.

    Thanks


    Don
    Found it.

    Just double checked my wiring....ground was left off the F2 terminal on the Alt.

    Thanks

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