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  1. #1
    I wired my machine to use the charge pump output so that the relay would only activate the motor psu if the software was active and not in a reset/error state. This has worked perfectly while testing until I tried it a couple of days ago. When I apply power the relay and therefore the motor Psu all spring to life. I checked all wiring and even stripped it all back to the bare minimum and tested again with the same issue. I have checked the charge pump isolated output and it appears to always be active even if the indicator LED is off? I have checked that the option to always enable charge pump isn't active and am now wondering whether it's faulty...does anyone have any other ideas?

    Sent from my SM-G920F using Tapatalk

  2. #2
    Does the other outputs work as expected ?

    Assuming the output transtor is open drain and grounds the relay coil terminal to switch the relay on

    With the power off you can use a multimeter to check the resistance between the negative supply terminal and each isolated output

    in the manual
    http://www.cncdrive.com/downloads/AXBB_E_manual.pdf
    see diagram 9.1.2 .Connecting a solid state relay (SSR)

    test between 24V0 and Ox

    You should find they are all open circuit unless the transistor controlling the relay is short circuited

    John
    Last edited by john swift; 11-08-2019 at 07:22 PM. Reason: correct typo

  3. #3
    Cheers John, I'll check the resistance tomorrow but one more thing I remembered. I also tried output 2 of the isolated outputs and that one does read the voltage change if I set that as the charge pump output however that one doesn't activate the relay? The manual states that the isolated outputs can drive upto 500mA so I'm assuming it's not enough power to drive the relay and the output 1 is different.

    Sent from my SM-G920F using Tapatalk
    Last edited by CharlieRam; 11-08-2019 at 07:41 PM.

  4. #4
    what relay are you using ?
    any idea what the coil resistance is ?

    This one from RS Components has a coil resistance of 650 ohms
    https://docs-emea.rs-online.com/webd...6b815856e9.pdf

    If the RS StockNo:450-0425 relay was used with the AXBB and its 24V DC supply only 37 mA would flow via the AXBB output

    John

  5. #5
    It's like the one below

    https://rover.ebay.com/rover/0/0/0?m...2F283248324744

    Sent from my SM-G920F using Tapatalk

  6. #6
    going by this data sheet
    Click image for larger version. 

Name:	MY2x4 relay data.pdf 
Views:	39 
Size:	578.7 KB 
ID:	26191

    your relay also has a resistance of 650 ohms

    page 4
    Non-latching – DC
    rated voltage = 24V
    rated current = 36.90 mA
    coil resistance = 650 ohms

    John
    Last edited by john swift; 11-08-2019 at 10:30 PM. Reason: add ref to page 4

  7. #7
    Forgive my ignorance but does that mean the other isolated outputs are all capable of driving the relay? I did check that and thought so but its been a while since I DoD electronics!

    Sent from my SM-G920F using Tapatalk

  8. #8
    Quote Originally Posted by john swift View Post

    With the power off you can use a multimeter to check the resistance between the negative supply terminal and each isolated output

    in the manual
    http://www.cncdrive.com/downloads/AXBB_E_manual.pdf
    see diagram 9.1.2 .Connecting a solid state relay (SSR)

    test between 24V0 and Ox

    You should find they are all open circuit unless the transistor controlling the relay is short circuited

    John
    It looks like I'm getting approximately 100 ohms on output 1 to ground, all other outputs are open.

    Sent from my SM-G920F using Tapatalk

  9. #9
    The reference to " other isolated outputs are all capable of driving the relay "

    differentiates the outputs from the 5V logic level outputs that you connect to other logic gates or the stepper driver step & direction inputs

    from the open drain outputs designed to switch inductive loads like the relays

    As an example
    Going back to equipment I used and maintained in the eighties
    all the logic was built from 7400 series TTL logic

    Typical gate inputs passed 1.6 mA when an input a input was grounded
    and the outputs could sink 16 mA
    so you could only connect 10 inputs to the output of an IC
    unless you used a buffer that could pass more current

    To connect to other devices like tally lights for the control panel switches

    A lamp “driver” / BCD decoder like the 7445 switched 28v bulbs ( run off a 24V supply ) by grounding the other end of the bulbs filament

    The 74141 being another version with high voltage outputs for driving Nixie tubes
    (which is basically a neon with an anode connected to 180V DC via a resistor and 10 cathodes shaped in the form of the digits 0 to 9 that glows when grounded )

    These days you would use a 7447 BCD to 7 segment decoder driver connected to a 7 segment LED display or LCD

    John

  10. #10
    It looks like the FET for output 1 has short circuited

    I would check you don't have a wiring problem that could connect the 24V DC to the AXBB output

    Did you check the relays coil resistance is 650 ohms as expected
    less than 48 ohms would pass more than the 500mA limit for the output

    John

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