dmorph

AB 753 Drive output signal failure

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We have an Allen Bradley 753 that isn't starting a motor. No faults, alarms or outstanding issues. Verified drive is receiving 0-10V signal, monitoring of drive amps proves drive attempts to send output signal to motor. No current leaving drive. Placed drive in manual mode, drive attempted to send output current to motor via drive explorer software monitoring of amps, no current leaving drive.  Verified edited parameters have not changed. Any thoughts what might cause this other than failed drive.  

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Do you have a speed reference to the VSD, check Parameter 2 when you tell it to run, then check Parameter 1 to see what the output frequency is.

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First off, get rid of that antiquated Drive Explorer tool and install Rockwell's free Connected Components Workbench (CCW). It's a far better and more user friendly drives tool, with many more features. And did I mention it's FREE?

It sounds like you're using a hard-wired 0-10VDC analog signal in for speed reference, and that you've at least put meter leads on the terminal blocks to verify it's not the wires. I will further assume that you've checked the for the obvious things like loose connections at the terminal blocks, particularly with any feedback devices, such as an encoder (if used). @alan_505 has set you down the right path to start with and the results you get from that check will determine what to do next.

  • If parameter 2 shows an incoming speed reference at or very close to 0 regardless of the voltage on the terminal block, check parameter 545 (Speed Ref A Sel) to make sure the drive is looking at the correct analog input. If it's not, fix it. If it is correct, remember that voltage on the terminal block doesn't automatically mean the drive can see that signal. Go to the analog input parameter (255 for the main control board, 54 & 64 for the 24v extended I/O card analog inputs) to view the raw data coming into the drive. If that's not changing to match what the multimeter says, your analog input channel is likely bad.
  • If parameter 2 shows an incoming speed reference that closely matches the actual input at the terminal blocks, check parameters 935 and 936, Drive Status 1 & 2. These are bit parameters that tell you at a glance what the drive thinks it's doing. All of the bits in these parameters are important but when I'm having symptoms you've described, I always look at P935 bits 4 (Accelerating), 5 (Decelerating), and 8 (At Speed), 26 (At Limit), and 27 (Cur Limit) first. For instance, assuming a correct and good input speed signal, if bit 8 is set and the motor is not moving, you'll want to check your motor's encoder (other feedback device) if you're using one. If it's damaged or has loose wires, the drive isn't getting the feedback it needs to let the motor draw more current. I once found bits 4 and 27 were simultaneously set because someone accidentally changed the current limit parameter to the minimum of 1. The drive was trying to run but no significant current was leaving the drive because the limit had been hit. No faults, no alarms, and no motion. 

I know you said you believe no parameters have been changed from their known good values, but these are all things that should be checked and positively eliminated as possible reasons for the failure. 

Keep us posted on your progress and I hope this helps. 

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Easiest thing is to compare parameter 1 and 2. If they match then revisit where the reference is coming from. If they don’t, use the block diagrams in the manual to see where the signal is being changed

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Any chance the IGBTs are blown?

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@pcmccartney1 if an IGBT was blown he'd almost certainly be getting faults. Not impossible to not have faults in that condition, but extremely unlikely, particularly with a PF753. The suggestions made above would lead the OP to that, if that's the condition causing his problems.

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so. is the drive showing that it's running? can you see the outgoing hz and monitor? 

check the commanded freq, and verify that it's outputting what you are telling it to output, if it's not. then you have an issue with control.

I'd hate to ask, but is the motor actually connected to the drive right? or was it disconnected and someone didn't notice? Because you can certainly run a drive with nothing connected, and see no output current.

 

when all else fails, reset all parameters and run the wizard to set it back up again from scratch. sometimes it's easier just to set it up yourself than try to guess what someone may have accidentally changed.

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