584,833 active members*
5,717 visitors online*
Register for free
Login
Results 1 to 6 of 6
  1. #1
    Join Date
    Feb 2010
    Posts
    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
    Join Date
    Feb 2010
    Posts
    11

    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
    Join Date
    Mar 2009
    Posts
    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
    Join Date
    Feb 2010
    Posts
    11

    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
    Join Date
    Mar 2009
    Posts
    533

    Re: Power question

    Are you getting an input voltage to the LM317?

  6. #6
    Join Date
    Feb 2010
    Posts
    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

Similar Threads

  1. 90 VDC Power question
    By walkabout in forum LinuxCNC (formerly EMC2)
    Replies: 2
    Last Post: 07-31-2013, 07:42 PM
  2. Power Supply Question
    By Dman65 in forum CNC Machine Related Electronics
    Replies: 3
    Last Post: 08-14-2009, 06:42 PM
  3. Stepper Power Question
    By Cartierusm in forum Linear and Rotary Motion
    Replies: 9
    Last Post: 10-22-2008, 08:06 PM
  4. stepper power question
    By endgrainguy in forum DIY CNC Router Table Machines
    Replies: 2
    Last Post: 03-04-2008, 05:41 AM
  5. Power Supply - Question
    By Yellowbeard in forum CNC Machine Related Electronics
    Replies: 6
    Last Post: 04-20-2005, 01:33 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •