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  1. #1
    Hi, I purchased an R86 stepper motor driver, however on trying to wire in the mains supply I found it had two live inputs but no earth. I am using a 24v power supply and I am now at a loss how to power this stepper driver safely. The little one page manual skips over this part of the wiring.
    Can anyone please help. Thanks

  2. #2
    phill05's Avatar
    Lives in Derbyshire  UK, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 9-10 years. Has a total post count of 287. Received thanks 26 times, giving thanks to others 12 times.
    You would connect earth to a star point on your enclosure

  3. #3
    Are you connecting mains to it or 24V? Am I right to assume 24v AC?

    As people may not know the details of an "R86..." it would help if you could provide details of a link, like this one:


  4. #4
    Thanks. So is it safe just to connect the earth to the metal box the breakout board, power supply and motor drives are housed in.

  5. #5
    This is a bit tricky, as you say the manual is unhelpful.

    Since it can be powered by AC it obviously has a built-in bridge rectifier. Conventionally the negative side of the output of this would be commoned to the metalwork of the box which would be grounded to the rest of the wiring ground. If that were the case, then you would NOT connect either side of the AC supply (from a transformer) to earth because if you did the rectifier diodes would be short circuited across the supply on one half cycle or another and would have a short if merry life! A/k/a a loud brown smell (guess how I know?). If you kept the AC supply isolated there would be no problem.

    With a DC supply, and if one side of the rectifier is connected to the driver case, then it would be OK to connect the same polarity of the supply to the case as the rectifier - one of the rectifier diodes would just not conduct as it would have a short across it.

    So it all hinges on how the internal rectifier is connected. My guess is that it would have its negative output connected to the case. To check you need a DMM with a diode setting in the resistance ranges - both my DMMs have this. Assuming they are typical the positive "V/ohms" input (usually the red socket/lead) should be connected to the case, then look at the reading when you connect the other (common, black) lead to either input. (A) if the meter reads a low value (on mine ~0.6) then the negative side of the bridge is connected. If not try the leads the other way round: (B) if you see a low reading this time it's the positive side. If neither gives a reading then (C) the case is isolated from the electronics.

    In cases A and C you can safely connect the case to the system ground. Case B is more difficult - do the measurement and see what you get, let us know and we can think again.

  6. #6
    Thanks, but due to total lack of manufacture information I have returned the unit. Thanks again

  7. #7
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 9 Hours Ago Has been a member for 5-6 years. Has a total post count of 388. Received thanks 50 times, giving thanks to others 9 times.
    Not really sure what the issue was here. The driver is clearly supposed to be supplied by an isolated AC (from transformer) or DC (from a PSU). The motor phase connections and that the output of the AC or DC supply will be floating with respect to ground, so you don't NEED to ground any of it. You CAN ground that circuit if you wish - for instance you might choose to ground the DC- side of the PSU is you went the PSU route. The output (motor phase) connections are not isolated from the AC/DC input to the driver and typical low voltage stepper motors are not designed and constructed to be connected to live mains, so electrical isolation between the mains and the drive voltage is required - this is provided by the transformer / PSU.

    This is normal practice for these low voltage drivers, so there's no obvious need for any information beyond what they've provided. It's really no different from any other low voltage stepper driver other than the fact it will accept either AC or DC on the input.

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