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Thread: Ammeter and other things

  1. #1

    Ammeter and other things

    Trevor,
    Firstly, some info that may be useful for other users:
    When we first started testing the set-up in the aeroplane we noticed something rather strange: Every time the PTT button was pressed the amps reading would plummet to -80! We found that an aerial that we had mounted inside the (wooden) fuselage was radiating. We switched to an external aerial and the errant display was gone.
    Now however we have a silghtly different problem in that the ammeter doesn't fluctuate from zero even when all consumers are switched on. Upon checking the wiring diagram I see that the shunt is only wired to monitor charging current and not consumer consumption and so the reading will only fluctuate if the battery is low and the alternator is pumping out full volume to compensate. Is this right? I'm not an electrician so some layman's clarity on what I should expect to see would be nice.
    Secondly, and not very important in the short term: whilst the engine is running one of my fuel guages fluctuates between 65 & 45 litres. It's very rythmic and so looks like it's picking up a spurious signal from somewhere. Any ideas?
    Colin

  2. #2
    I put a shunt on the alternator and a HAL effect transducer on the main Bus.
    From that, I get alternator output and mainbus draw. Subtract and you have what is going to the battery.

  3. #3
    This is a correct interpretation. The shunt is on the alternator side of the bus, so you will only see an amp reading when the engine is running.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  4. #4
    Ah, but the point is that I don't see anything other than zero. Is that right? The voltage reading increases when I switch the alternator on so it's definitely charging.

  5. #5
    It sounds to me like your shunt may either have an issue, or the wires are not connected to it. If you go into Instrument Calibration mode and select AMPS, what is the AD_Value? Does it change when you turn on various electrical devices (engine running)?
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  6. #6
    Here's a picture of the ammeter in calibration mode. Unfortunately I didn't take note of whether the value changes when I load it up or not but perhaps this image might give a clue?



    Well, for some reason I can't seem to upload the picture and yet the video works well?

    I'm also frustrated to report that my problem (mentioned above) with PTT affecting ammeter reading is back despite now being connected to an external aerial.
    See here:

    Any ideas?
    Last edited by stickandrudderman; 08-22-2011 at 05:11 PM. Reason: as described

  7. #7

  8. #8
    If PTT is affecting amps, it sounds like a grounding issue. Do you have at least an 18 gauge wire connected to the ground screw on the back of the EFIS? Do you have a good ground plane for your COM antenna? Are you sure your alternator/engine/engine mount are grounded well? This type of issue always comes down to poor grounding.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

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