tingG Chip U8 Gets Smoking Hot!

Home › Forums › TinyG › TinyG Support › tingG Chip U8 Gets Smoking Hot!

Tagged: 

Viewing 13 posts - 1 through 13 (of 13 total)
  • Author
    Posts
  • October 9, 2015 at 5:10 pm #8834
    robertk925
    Member

    Hi. I was reaching for the reset switch to upgrade the firmware on my tinyG, and accidentally touched the U8 chip (next to the 3 pin fan connector). It was smoking hot, even after I had just turned on the tinyG for a few minutes! I am familiar with electronics so I know that some chips run warm, but this was burn the skin hot, which I can’t imagine is a good sign for the long term reliability of this chip. I will check it with an IR thermometer later on, but I wanted to ask if this is normal behavior or not? Thanks!

    October 9, 2015 at 11:03 pm #8835
    cmcgrath5035
    Moderator

    U8 is a Vmot to 12V Linear Regulator.
    Are you powering something more than a fan?
    Schematic

    October 11, 2015 at 9:24 pm #8837
    robertk925
    Member

    Thanks for the reply Carl. No, the fan (90mm 12V) is the only thing I am powering. The tinyG is running 3 steppers (X, Y, and Z axes), but the U8 chip gets hot when I first turn tinyG on and haven’t even driven the steppers yet.

    October 11, 2015 at 9:48 pm #8838
    cmcgrath5035
    Moderator

    If you disconnect the fan there should be no load on U8.
    You don’t need a fan for an idling tinyG (steppers not running).
    So unplug fan, If tU8 stays hot there is a short/miswire on the board or U8 is bad.

    October 12, 2015 at 12:36 am #8839
    robertk925
    Member

    Excellent, I will disconnect the fan and report back.

    October 13, 2015 at 6:52 pm #8846
    robertk925
    Member

    I disconnected the fan and the chip stays cool. So, I guess I should use a smaller fan?

    October 13, 2015 at 9:44 pm #8847
    cmcgrath5035
    Moderator

    How big a fan are you running?
    I use a 92mm TT9025A 2.64w (rating .22A max) fan that blows down directly on top of tinyG, so the LM7812 benefits from the airflow as well as the driver devices.
    Since it is 24 V to 12V , the regulator will be dissipating about 2.64W as well.

    I honestly can’t say I have touched around that area, I am sure it is warm but yours sounds much worse.

    October 15, 2015 at 8:46 pm #8850
    robertk925
    Member

    My fan is 80mm, .30A max, 12V. It blows below the tinyG, as I thought the pads on the bottom side of the board were the heatsinks for the stepper drivers?

    October 16, 2015 at 7:45 am #8851
    cmcgrath5035
    Moderator

    The drivers are in a “Power Pad” smt package, you can read about them here:

    So what you see on the bottom of tinyG are the recommended connection points from the package to the ground plane, which acts as a heat sink
    You could also fashin a heatsing and attach to that pad as well.
    Blowing air on the board is usually adequate.
    U8’s thermal tab also connects to the board for heat sinking.

    Seems a rather inefficient fan, a quick look into my junk box sees a couple 80mm fans in the .16-.19A range. Maybe just try a different one?

    I don’t think blowing on top vs. bottom would make all that much difference, actually bottom might be better
    I have one of each, fan mounted approx 0.75″ from the tinyG surface

    October 16, 2015 at 12:01 pm #8852
    robertk925
    Member

    Great, thanks for all of your help Carl. I will try to scrounge up a different fan.

    October 16, 2015 at 1:56 pm #8853
    cmcgrath5035
    Moderator

    Here are results of a quick test on my tinyGV9, next gen platform but the fan drive same, however the regulator device is physically smaller.

    I have an older ultra thermoflow 80 mm 2500 rpm fan blowing up on the bottom of the board. Spec is I believe 2.16W max.

    I can hold my index finger on the regulator for “1001-1002-1003” before my brain says ‘hot, ouch coming’.

    October 17, 2015 at 10:33 pm #8855
    robertk925
    Member

    Thanks Carl, that is helpful. I haven’t had time to try another fan. I also still need to measure the temperature of the top of the chip with my IR thermometer.

    October 21, 2015 at 11:21 pm #8866
    robertk925
    Member

    I hooked up a tiny 50mm fan and U8 doesn’t run hot anymore, so it must have been the original fan I was using. Thanks!

  • Author
    Posts
Viewing 13 posts - 1 through 13 (of 13 total)
  • You must be logged in to reply to this topic.