Danfoss FC51 Output Issue

janner_10

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This is the first time I've had the pleasure of setting one of these up.

It's a little 1.5kw, 3p 400v one running a centrifugal fan, 1.1kw motor.

It's speed reference is via 0-10v Analogue Input, which is coming in nice and steady, however the drive output is not steady at all.

It will fluctuate for around 90s, +- 5% around the desired SP, but will settle down eventually, until the speed is changed again.

The drive is set up with all the correct motor parameters, I've done AMT as well, so I'm at a loss.

Any pointers from someone familiar with Danfoss shine a light?

What would of took me 10 minutes with a PF525 or a V20, has so far consumed today, well until 2pm until I went home!
 
Can you try running it with a keypad reference to see if the behavior remains?

Also, there should be a way to display the analog voltage reference signal the drive is sensing.

I have not used that model, but have worked with some of their other drives and they have been pretty good in my experience except for the stupid "one-time use" microscopic terminal blocks.
 
The speed Ref readout pretty much mirrors the AI Signal, so I've no concerns on that front.

Good point about the Keypad Ref, I will try that Monday.
 
This is the first time I've had the pleasure of setting one of these up.

It's a little 1.5kw, 3p 400v one running a centrifugal fan, 1.1kw motor.

It's speed reference is via 0-10v Analogue Input, which is coming in nice and steady, however the drive output is not steady at all.

It will fluctuate for around 90s, +- 5% around the desired SP, but will settle down eventually, until the speed is changed again.

The drive is set up with all the correct motor parameters, I've done AMT as well, so I'm at a loss.

Any pointers from someone familiar with Danfoss shine a light?

What would of took me 10 minutes with a PF525 or a V20, has so far consumed today, well until 2pm until I went home!
Are you using the internal PID (or just PI) control loop in the drive? If so, your Integral function might need adjustment.
 
Are you using the internal PID (or just PI) control loop in the drive? If so, your Integral function might need adjustment.

Neither, I just want the damn thing to run at the speed I tell it to.

EDIT: It is set to Speed Control Open Loop.
 
Have you monitored motor current when this is happening? Current Limit or Over Load or Stall Prevention situations can often elicit a response from the VFD of overriding the speed setting to keep from tripping. I don't know how that might work in that drive, I'm not that familiar with it, but that's a common feature.


PS: Looking at the manual for this drive, their equivalent that might do this is Torque Limit, 4-16. The factory default is 150%, if someone set that lower, it might be causing this as a response. They don't actually tell you what Torque Limit does, but it implies this because in the Ramp Time (3-41) setting it warns you to make sure your Ramp Time is long enough to avoid it going into Torque Limit, probably because Torque Limit will artificially alter the Ramp Time.
 
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