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Thread: Bad Hall Effect sensor for Amperage reading?

  1. #1

    Bad Hall Effect sensor for Amperage reading?

    Dynon and AFS tech support must be backed up so here is a question for the gurus.

    On my 3 year old AFS built panel, with an ACM and a hall effect sensor for amperage, I have had the readings drop off dramatically lately.
    My baseline load in cruise was running about 15 to 20 amps until 3 months ago when it started to give me low current warnings.
    The current drops to about 2 amps after about 10 minutes of running regardless of whether in the air on on the ground.
    I checked out the B&C 40 amp alternator and it is OK.
    Then I put a clamp on amp meter around the power cable next to the hall effect sensor.
    Long story short, the hall effect sensor reads 13 to 15 amps lower than the clamp on meter.

    Question: Can anyone think of a reason other than a bad sensor that might happen?
    I'm reluctant to put in a calibration offset of that large a value.
    I probably need to order a new one and swap it out but thought I'd ask prior to the effort and gymnastics involved in doing that.
    BTW: I do know about the recent sensor letter and mine is not affected, I do have the screws in place on it.
    Thanks in advance.
    Mike H

  2. #2
    Check the sensor with a multimeter. With 0 current flowing through the b lead you should have 8V coming in to the sensor from the EMS-220 C37 pin 15, and you should have 4V coming out the signal wire and going back into the EMS-220 C37 pin 31. What are your actual numbers?

  3. #3
    Hello Jonathan
    Thank you for the prompt reply, this is excellent information. I do have a couple of questions.
    Q1: Should this be collected while the engine is running or with the engine off?
    Q2: When you say b-lead I assume you mean with the alternator b-lead disconnected, so no current is going through the cable through the coil?
    Q3: So how do I get to these pin voltages with the plug installed into the ACM, with or without the engine running?
    I ask because there are some serious gymnastics involved with getting to the ACM behind my Glastar panel.
    I'll look at it today.
    Thank you.

  4. #4
    leave the b-lead connected to the alternator, there will not be any current flowing through it provided you have the engine and alternator field both turned off. If the sensor is in an accessible location, probing at the "+" and "OUT" solder pads on the circuit board would be best. Failing that, nick the insulation somewhere along the wires coming out of the EMS-220 and probe there.

  5. #5
    Hi Jonathon
    Here is the update. I pulled off the hall effect sensor from the alternator cable and left it dangling.
    I powered the ACM and the panel from a large DC power supply.
    The engine was not running.
    The sensor gets 8 volts on the input side and 4 volts on the output side.
    I was sure that it was bad and couldn't believe the readings so I checked it multiple times.
    The only thing I didn't do was let it run and warm up for 10 minutes, or half an hour, before the readings.
    Now the way it always fails is to start out correctly and then it drops after about 10 or 15 minutes to about 2 to 5 amps reading.
    I'll do that tomorrow, however my question is; should it be in place with a power cable running through it or still without the cable?
    I can do it both ways I suppose but I'm curious what you think.
    Mike H

  6. #6
    I have already stated once that you ought to leave the b-lead connected and running through the hall effect sensor. With the alternator off and therefore no current on the wire, you should have 4V on the sensor signal line, as you have measured. Voltage on the signal line will decrease as amps on the measured wire increases from zero.

    Is this 10-15 minutes after you turn on the EFIS that the readings start going awry, or 10-15 minutes after you turn on the engine (and alternator)? Where is your hall effect sensor installed? Is it near to anything else that might conceivably generate a magnetic field?

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