CharlesIsWorking (Customer) asked a question.
GS23-4030 - drive tries to slow down motor when doing a Stop/Start
Hi all,
I have a GS23-4030 which is driving a 30hp motor connected to a large material chopper fan. Motor parameters are set in the 5.0x settings. Ramp up time is 20 seconds. Coast to stop is set. Linear accel/decel. Standard Hz settings with 60hz max.
It is set to 2-wire config with terminals DCM-->switch->FWD.
Coast to stop works fine when starting the drive and hitting stop. If I hit start again while the fan is spinning, it tries to slow the motor down before ramping up. I would like to have it take whatever rpm the motor is at and work with that to get it up to speed, and not try to slow it down in order to run it.
What settings should I be looking at?
Thanks
I don't think the VFD is intentionally trying to slow the fan down first and then start ramping up faster, it is simply a product of the VFD thinks motor is at 0hz and that is where the ramp starts, so when you hit the start switch the ramp profile starts and thus the frequency sent out to the fan is at a much lower RPM than it is currently. The VFD has little ways of knowing the inertia RPM of the load, and is just running through its ramp profile.
You may be able to let the VFD know the load's RPM by using a mode with feedback to the drive as to load RPM. It may be possible with a sensorsless vector, but in the end you may simply have to use an encoder as feedback.
I dont know for sure even an encoder would automatically alter the starting Hz and ramp profile, though Id assume it should to an extent since it known the feedback RPM at startup. See chapter 4, page 4-220 of the manual for encoder pulse feedback for the GS20 series drives:
https://cdn.automationdirect.com/static/manuals/gs20m/ch4.pdf
Looks like it only takes a single ended pulse feedback instead of a real encoder signal.
You may be able to set the min hz to greater than zero and it may start its accel from there.
Thanks to you both for the responses!
After a call to support and some testing, we decided to set the drive to Ramp to Stop, with a decel time in 01.13 that matches the coast to stop time of the fan.
When the drive is set to ramp to stop with an appropriate time so that it's not doing much braking, it keeps track of its driving RPM's and can accel from that deceleration ramp at any point.
Bill from Support also suggested something similar to what PurchesInc talked about, which is informing the drive somehow of the RPM's through an input. Shout out to Bill for the help!
Some drives have a "catch a spinning motor" function, However, I could not find a parameter in your drive that would do that. Maybe I missed it?
Sometimes called "flying start". Might require sensorless vector mode to work, but I also didn't find a description of that function for the GS20.
Thanks for the replies. Yeah I wonder if the GS23 4030 would need sensor feedback in order to always "know" so for now, setting the ramp down to somewhat match the real world coast down is good enough for what we need.