# PF 700 flying start gain



## 4play (Feb 26, 2010)

I am trying to get a 30HP Powerflex 700 to do a flying start. This VFD also has a dynamic brake resistor on it. I have the flying start enabled but it still starts at 0 Hz. The motor is being pulled along by a sheet of paper and cannot be stopped. When it starts at 0 Hz, the drive sees regen voltage from the motor and starts dumping it to the brake at the same time it is trying to start. What part does the flying start gain have on the PF 700?


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## John Valdes (May 17, 2007)

Contact the vendor and go over the parameters for the flying start. It sounds like a programming issue to me.
AB or agent of AB can easily walk you through the procedure. 

Does AB allow downloading of manuals? That would be the only way I could help you on this.


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## MDShunk (Jan 7, 2007)

Makes me wonder if you don't have F-forward and F-reverse settings backwards. It could be seeing that the motor is still flywheeling, but thinks it's flywheeling in reverse. That's the only reason I can think of for it to try to brake. 

You running this with an encoder or not? If you're using this for paper web control or something like a slack tower, my guess is that you're also using an encoder. Could be as simple as encoder polarity backwards (or the wrong encoder for the drive). If the encoder was bass ackwards, it might think it's flywheeling in reverse, try to brake it, then go "forward". That would probably trip out the drive, though.


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## 4play (Feb 26, 2010)

MDShunk said:


> Makes me wonder if you don't have F-forward and F-reverse settings backwards. It could be seeing that the motor is still flywheeling, but thinks it's flywheeling in reverse. That's the only reason I can think of for it to try to brake. quote]
> 
> Can you elaborate on the above quote just a little. I don't recognize those parameters. Also, no encoder on this drive. This is a new install and I've even swapped the drive out with another. (was running out of options) Luckily, once I get it started it runs fine, but it's a bit of a bugger to get it going. Since the motor is generally always spinning (from the paper) I just set the ramp up time to a couple seconds and it will start.
> 
> ...


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## John Valdes (May 17, 2007)

Quit busting your own balls and get on the phone with the vendor. Why waste all this time when you could have had this fixed last Friday.

There is support and you better get used to using it. No one knows everything. So call that guy that comes over now and then and takes your boss out to lunch. Tell him you need some help. If he cannot provide programming support over the phone for free, you need a new vendor.


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## varmit (Apr 19, 2009)

Hello,

You say that you want to do a flying start in a web handling application with no encoder feedback? Without an encoder, the drive would need a analog input as to what the web speed is currently in order to match the speed of the web on a flying start. Depending on the dynamics of the application, torque mode may be a better option, but would still require an input for what line speed to match on a flying start. Unless there is some sort of of dancer ( or some slack provider ) there may be a web break potential until the motor matches line speed. Is this motor always started after the web is in motion?


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## varmit (Apr 19, 2009)

In your current setup, with the drive having no way to know the line speed on start, the drive will start at 0 hertz, or whatever minimum speed is set for. The drive is starting into an overhauling load so it will gate to the breaking resistors until it can accelerate to line torque demand.


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