Need advice on troubleshoot DC motor

Discussion in 'The Projects Forum' started by tsoi_cabbage, Mar 18, 2014.

  1. tsoi_cabbage

    Thread Starter New Member

    Mar 18, 2014
    Hi, I’m troubleshooting some intermittent failure and would love to get some advices please!
    The spec for the motor is 5mA to 100mA.
    Power source is ~3V powered from the USB.

    I confirmed all the motors functions (read ~20mA) prior installation to a housing (glued with epoxy and cure at 70C for 2 hrs), after cured, 2% of the motors has intermitten failure that reads below 5mA, however once i removed the motors from the housing, they passed again.

    I checked there was no short on the wires.
    Resistance within spec while installed in the housing.
    I tried to installed the "failed" motors in the housing again with and without epoxy - still passed

    I then repeated the test with kapton tape on the housing, still got the same failure, where the motors would failed only when installed in the housing but passed after removing from housing.

    Anyone has any idea what could cause the intermittent failure? The housing are made in AL and the fallout is always ~2% no matter how big the sample size or trials i did.

  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    Can you post some photos, spec sheets, schematics of the system?

    It's really difficult to help you without more information, but I am guessing the epoxy may be shrinking, putting stress on the motor housing.
  3. MaxHeadRoom


    Jul 18, 2013
    What is the motor technology?
  4. tsoi_cabbage

    Thread Starter New Member

    Mar 18, 2014
    Hi, sorry I'm new here, is it possible to post print screen?? Because the doc I have are in PDF, not sure how to insert them here.

    Motor description:
    Cylindrical Type, DC, 93Ohm, without boot

    Epoxy: Resinlab EP1290T2, it does has a dielectric constant of 6.5 and other preperty such as thermal conductivity, dielectric strength, etc.

    Application: after cured, power the vibe with ~3V supply from a battery-PCBA-USB cable thru a computer and measure the vibe current over 5 seconds with a LabView program.

    The passing requirement is >5mA, but some of them will give a <5mA within the 5 second period. When I removed the vibe from the housing, the "failed" ones will pass again.

    I then reinstall the vibe in the housing and measure the current - tried wiggling the wires, apply pressure on the wires but I couldn't get them to failed again. I'm trying to duplicate the failure with the "failed" vibes without success.
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    If that's true for the 'failed' vibe, and the current is <5mA, that suggests a poor (i.e. high resistance) connection in the supply from the test jig.
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    These are vibrator motors?

    You may have a mechanical coupling issue.

    The amount of power a vibrator motor needs is affected by how it is mounted.