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Thread: Current shunt

  1. #11
    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by turbopilot View Post
    Input of alternator to the 50 amp alternator CB.
    Thanks. I was well on the way to planning the mod and then I did a reset. Top level requirement seem to be to alert as soon as the alternator stops supporting the full system load. When that happens the battery will start to discharge but its voltage won't immediately drop to alert level.

    What I did, perhaps interim and perhaps final, is to change the alerting levels for the existing battery current shunt. I have set it to produce a CAS alert any time the current is zero or negative (battery not charging). This means it will always alert before engine start but should never be active in flight unless there is an alternator system failure.

    I saved the config file and made screen shots before making the change so it's easy to go back if I don't like it.

  2. #12
    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post

    What I did, perhaps interim and perhaps final, is to change the alerting levels for the existing battery current shunt. I have set it to produce a CAS alert any time the current is zero or negative (battery not charging).
    Good idea. I did this a few weeks ago. It is a good work around. One of my goals was to get a full time indication of alternator health showing up in the EIS strip. I have had several alternator failures over the years. So far I have never had a complete failure, instead I have had alternators that experienced partial failures only discoverable by watching the amps output of alternator. For a total failure a CAS alert signaling a discharging battery is a good backup. I was able to make room for extra information in the EIS strip by deleting manifold pressure from the EIS as it is not too useful in an airplane with a fixed pitch prop. Manifold pressure still shows up on the engine page but it can be deleted from the EIS.

    $40 for a shunt and a few ounces of weight seems like a good trade for full time monitor of alternator health.
    Bob Anderson, CC11-00435, N94RA

  3. #13
    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by turbopilot View Post
    Input of alternator to the 50 amp alternator CB.
    I'm still thinking of doing this mod and have been looking at the details.

    The feed to the alternator CB is shown as #8 wire although the other wires in the alternator circuit are shown as #10. Seems appropriate to connect the new shunt to the CB with #8 wire with a 1/4 stud terminal at the shunt end and #8 stud terminal at the CB end. Aircraft Spruce doesn't seem to have #8 wire #8 stud terminals but I did find they are available from Mouser.

    Did you have someone make this link for you or did you have the appropriate terminals and crimp tool "in house"?

  4. #14
    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post
    I'm still thinking of doing this mod and have been looking at the details.

    The feed to the alternator CB is shown as #8 wire although the other wires in the alternator circuit are shown as #10. Seems appropriate to connect the new shunt to the CB with #8 wire with a 1/4 stud terminal at the shunt end and #8 stud terminal at the CB end. Aircraft Spruce doesn't seem to have #8 wire #8 stud terminals but I did find they are available from Mouser.

    Did you have someone make this link for you or did you have the appropriate terminals and crimp tool "in house"?
    I have a crimp tool and used #10 wire for the short runs to the shunt.
    Bob Anderson, CC11-00435, N94RA

  5. #15
    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    I set the alternator amps to "Red+Alert" anytime the alternator is putting out 5 or less amps. In my G3X SS with a fully charged battery, alternator output is 5 amps with wigwag landing lights, navigation lights and strobes all off. So for routine use I am finding that by the time I get to the run up area the battery is fully charged after starting and I will get a CAS alert for low amps if I have forgotten to turn on the strobes and/or wigwag lights. Good reminder to have those items on for take off.
    Bob Anderson, CC11-00435, N94RA

  6. #16
    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Another approach to current monitoring.

    I used an AMPLOC KEY100 hall effect sensor for alternator current. Simply unscrew the alternator lead from the circuit breaker, slip the sensor over the lead, then replace the lead on the circuit breaker. I used an AMPLOC AMP25 sensor for pitot heater current and have made provisions for another AMP25 sensor to monitor emergency ignition battery current. Each uses a customized general purpose input of the GEA 24 leaving the shunt input free for future use.

    BAT and ALT amps.PNG


    pitot amps.PNG

    I'll probably tweak the meter colors and alert zones. This was the first engine run to make sure everything was working.

    Installing the sensors is easy. Working on the GEA 24 connectors not so much. If I were building an EX with Garmin G3X I'd wire every GEA 24 pin I thought would ever be needed during the life of the airplane. I'd rather carry a few ounces of unused wire than have to work on those connectors after the boot cowl is fitted.
    Last edited by Andy; 04-21-2021 at 06:03 AM.

  7. #17
    Senior Member turbopilot's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by Andy View Post
    Another approach to current monitoring.

    I used an AMPLOC KEY100 hall effect sensor for alternator current.
    Good job. Do you have a link to the Hall effect sensor source?
    Bob Anderson, CC11-00435, N94RA

  8. #18
    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by turbopilot View Post
    Good job. Do you have a link to the Hall effect sensor source?
    https://amploc.com/

    A few notes that may be of interest to anyone who decides to use these sensors:

    AMPLOC uses square pins with 0.1 inch spacing. You'd think the pins would all have the same rotation angle so the flats would lie in one plane. They are in fact at random rotation angles. AMPLOC sales expressed surprise that this bothered me and said no one had ever complained before.

    I used readily available 3 pin connectors but this required modifying each sensor by adding the mating connector keying tab. These connectors will mate despite the random rotation angles of the sensor pins. The sensor keying tab was created by taking a standard mating connector, extracting the pins, drilling out the holes with a #55 drill (drill size corrected from #60), then milling off the body to the depth required for the pins to pass through to full depth.

    Output voltage depends on the sensor excitation voltage. I measured 4.99V out of GEA 24 with an uncalibrated multimeter. You must measure the zero amps sensor output voltage and compute the calibration points for that exact offset. It's not Vcc/2 as defined in the data sheets.

    There may be some drift in sensor calibration. I constructed calibration points to provide a dead zone at zero current to avoid the annoying display of values very close to zero when no current was flowing.

    Photo showing AMP25 sensor with added keying (KEY100 mod is similar):

    AMP25 with mod.PNG

    Photo showing pitot heat components:

    IMGP0521.jpg

    Photo of KEY100 sensor before modification. The black plastic flange was cut off and replaced by modified mating connector half:

    KEY100 before mod.PNG

    Second verse same as the first verse:

    IMGP0523.jpg
    Last edited by Andy; 04-18-2021 at 07:09 AM.

  9. #19
    Junior Member JohnC's Avatar
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    Default Re: Current shunt

    I like the idea of a second shunt for monitoring the alternator output. But I'm thinking of putting the shunt between the circuit breaker and the main bus. That way if the C/B pops or fails, I get a low output warning. Also, I don't have to contend with the 8 gauge wire. Any thoughts?

  10. #20
    Senior Member Andy's Avatar
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    Default Re: Current shunt

    Quote Originally Posted by JohnC View Post
    I like the idea of a second shunt for monitoring the alternator output. But I'm thinking of putting the shunt between the circuit breaker and the main bus. That way if the C/B pops or fails, I get a low output warning. Also, I don't have to contend with the 8 gauge wire. Any thoughts?
    The failure of the circuit breaker is just the same as the failure of the alternator to produce any output. It does not matter whether the shunt is before or after the circuit breaker. The current will be zero anywhere in the alternator load path. (The shunt is measuring current not voltage).

    The idea that a lighter gauge wire can be used if the shunt is between the circuit breaker and main bus may be false. This wire is only smaller because it is very short. If this link is extended by the length needed to insert a shunt it may need to be heavier gauge.

    Using either a shunt or a hall effect sensor requires access to the GEA 24 connectors. A hall effect transducer can be used with no changes to the high current alternator output wiring. Shunts are more expensive and harder to install. It was an easy choice for me.

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