ericn (Customer) asked a question.

November 19, 2021 at 8:30 PM
On the GS20 drives, are the SCM and DCM terminals isolated?

Based on the magic smoke that came out of mine, I'm guessing no?

 

I've used a number of GS20 drives with no issues, but I always connect both the SCM and DCM terminals to my 0V, then supply +24V to the STO terminals through a safety relay, and switch +24V to the DI terminals via my sourcing PLC outputs (with the switch set to PNP).

 

For this project, the customer specified NPN outputs on the PLC. Therefore, I connected +24V to the DCM terminal, and switched 0V to the DI terminal via the PLC's sinking output, as shown on page 2-36, lower left (switch set to NPN). I kept the safety input wired my standard way as described above, so +24V was on DCM, and 0V was on SCM. Quite the smoke show!

 

I already ordered a replacement drive (hope the ship date holds true!), and will add an interposing relay this time, using the drive's power for the DI.

 

Just wondering if this was the cause. Now that I look at it, the +24V terminal for the STO (red terminals) and the +24V for the DI are both labeled +24V, so their 0V terminals (xCM) are likely the same potential. If so, then I feel they should have the same name (maybe 0V or COM).

 

While I'm on the subject, does the analog common (ACM) also share the same potential as SCM and DCM?

 

I looks like only the I/O board got damaged, so I'm saving the drive for future spare parts.

 

-Eric

  • 9 answers
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mastmach likes this.

  • ADC_DriveMotorsLSPLC_PM (AutomationDirect)

    The SCM and DCM terminals are tied together with the same potential. The ACM terminal does not share the same potential as the SCM and DCM. 

     

    Your message did alert us to an error in the manual regarding the NPN sink mode diagram on page 2-36. +24V power is shown wired to DCM terminal, but it should be wired to +24V terminal. We will get this updated in the online manual this week. Correct diagram is attached below which also shows a diode that the original diagram did not show.

     

    Was the replacement drive you ordered sent as a warranty replacement? If not, we will be glad to replace your destroyed drive with a new one, as this was an error on our part. I apologize for this.

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    • NPN Sink
    Selected as Best

  • ADC Community_02 (Automationdirect.com)

    Sorry for the delay on a response. We are awaiting an answer from our Vendor on your question(s).

    • ericn (Customer)

      No rush. I just got an updated delivery for the drive. It is now scheduled to ship 12/8 instead of today.

    • ADC_DriveMotorsLSPLC_PM (AutomationDirect)

      The SCM and DCM terminals are tied together with the same potential. The ACM terminal does not share the same potential as the SCM and DCM. 

       

      Your message did alert us to an error in the manual regarding the NPN sink mode diagram on page 2-36. +24V power is shown wired to DCM terminal, but it should be wired to +24V terminal. We will get this updated in the online manual this week. Correct diagram is attached below which also shows a diode that the original diagram did not show.

       

      Was the replacement drive you ordered sent as a warranty replacement? If not, we will be glad to replace your destroyed drive with a new one, as this was an error on our part. I apologize for this.

      Expand Post
      • NPN Sink
      Selected as Best

      • ericn (Customer)

        Thanks for the detailed reply. That drawing is much clearer! I'll be on the lookout for the updated manual.

         

        I did not send the drive back as I thought the damage was my error. The drive was purchased by my customer, but I ordered the replacement drive through my account.

  • Todd Dice (Customer)

    Oof, that is a good question and an unfortunate way to have to ask. I, like you, always use inputs as PNP. Thinking about it, I have never seen in documentation for any drive I've used (PowerFlex, Yaskawa, GS1, GS2, GS3, GS20) describing the inputs as sink/source.

    • ericn (Customer)

      Check out this picture from page D-3 of the GS20 manual. The text says DIC terminal, but the picture says DCM terminal twice. There is no digital input common (DIC) terminal on the drives, only two DCMs as pictured. If there were separate terminals, I don't think I would have smoked this drive, as I would have connected my external +24V to the DIC terminal, which appears to be isolated in the picture.

      • DIC

  • PouchesInc (Customer)

    I have always used NPN output PLCs. The way I wire them is to not connect anything to the +24v terminal on the drive, and take the DCM and connect it to my external power supply's 0v side. That 0v goes to all the commons on the PLC for the different groups of outputs, and my PLC output gets wired right to the DI# terminal I want to switch on with the PLC.

     

    I have never had a problem doing it this way, and I recently deployed a GS20 drive with a P1k PLC in a project wired in this manner. Looking at the GS20 documentation, it does have a lot more wiring examples than I am used to seeing, and the way I did it doesnt exactly look correct for how the spec sheet shows things. However, I have normally used GS1 drives and a couple of GS3's, so that is where I first learned how to wire them and both of those drive series spec sheets show things how I have always done it.

     

    page tGSX-6:

    https://cdn.automationdirect.com/static/specs/gs1drives.pdf

     

    page tGSX-65:

    https://cdn.automationdirect.com/static/specs/gs3drives.pdf

     

    page tGSX-24:

    https://cdn.automationdirect.com/static/specs/gs20drives.pdf

     

     

     

    edit: Quick little mockup in MS Paint showing how I wire my sink output PLC to GS drives set to sink mode:

     

    GS20_wiring

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    • ericn (Customer)

      Yes, I should have wired it as you show. I have done similar when sharing different voltage power supplies, like a 5V supply for a stepper drive connected to a 24VDC sinking output card.

       

      Your last link shows what I think led me down this wrong path. In the bottom left diagram (page tGSX-24 'Sink mode with external power'), it shows +24V connected to DCM, and the 0V going to the PLC outputs common. I think this method would have worked if I didn't ALSO use the safety inputs with the same external supply. For reference, they show the STO wiring with an external supply on page E-3 of appendix E.

       

      https://cdn.automationdirect.com/static/manuals/gs20m/appxe.pdf

       

      As I said before, I have connected the STO circuit like this on other projects, but I was using sourcing outputs to control the DI, so DCM and SCM were both connected to the same potential (0V).

       

      Actually lately, I don't even connect anything to the DI terminals. I just use Modbus over the RS485 port to control the drive. So much simpler. Unfortunately, for this project, the customer requested discrete inputs to the drive, and sinking (NPN) PLC outputs.

       

      Thanks for your comment!

       

      -Eric

      Expand Post

  • g.mccormick (Customer)

    Ive never burned one up, but have had issues getting it all correct before when trying to ​use do output directly to vfd inputs. I always use interposing relays now.

 

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