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  1. #1
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    Feb 2010
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    11

    Power question

    I have a 4 axis hobbycnc board running on a 36v transformer. In the middle of a cut today the driver board quit responding. I have been trying to trouble shoot it and have a question. My 36v power supply feeds ac to a bridge rectifier with a large cap and then feeds the resulting dc to the power input on the driver board. The board is marked as 36v max and even though I measure 36vac on the output of the transformer I am getting 50vdc after the bridge rectifier. Do anyone have any idea why I would be getting the 50vdc and I assume that this will cause the board to shut down.
    Thanks.
    Mike

  2. #2
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    Re: Power question

    When it first stopped working my cooling fan was not running. I swapped the transformer out for a 24v one and now my fan is working but I still do not have motor control. I have requested a set of instructions from Brian so I can go through the board and see if I can find a bad component.
    Mike

  3. #3
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    Mar 2009
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    533

    Re: Power question

    Your transformer is said to be 36VAC. If so, the peak voltage will be 1.414 X 36V = 50.9Volts.
    The bridge rectifier will give a small loss due to diode voltage drop and the capacitor will charge to the peak voltage after the bridge rectifier.
    Your measurement confirms this.

    Yes, over driving the board is a bad thing to do. It may have damaged your board.
    What you need is a transformer that gives 36 / 1.414 = 25.45VAC.or use 24VAC as the next closest under 25.45 VAC.

    EDIT:
    Some transformers are designed to give the stated voltage under load, but could go higher by 10% under no load.
    Then your local power line voltage could also be be high under certain conditions thus possibly driving your output another several % higher output. These variables are hard to predict, so accurate measurements can help here to make decisions.

  4. #4
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    Feb 2010
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    Re: Power question

    I am not getting 5v on the 5v pad. I have replaced the LM317 but still am not getting 5v. I guess I need to pull the two resistors and check if they are good.
    Mike

  5. #5
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    Mar 2009
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    533

    Re: Power question

    Are you getting an input voltage to the LM317?

  6. #6
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    Feb 2010
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    11

    Re: Power question

    Turns out my board is fried. 2 of the drive chips are burnt up. I will be ordering a new board and if they are available I will get some replacement components and try to fix this one for a spare.
    Thanks for the help.
    Mike

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