control 8 Powerflex 4 thru RS485, should I use Contact Relay (Gold Flash) to start ??

Hi everyone,

I have a questions,
I'm going to control 8 VFD Powerflex 4 through RS485. And I can start each VFD by msg thru RS485, but never do it with all 8 VFDs.

Should I use Contact Relays to start them and MSG to control Speed ?

Or Contact Relays are wasted (I think it's a waste), just go ahead and start them by RS485 network ?

So if I start them all by RS485, just access the address of each knot and control them seperately or they have to control by series ? (start VFD1 , then VFD 2, ... then command speed VFD 1, VFD 2, .... )

Control each of VFD seperately (access the knot address) will harm anything in the future ?? or I have to control them in series ?

Thanks

We control the start/stop of our Powerflex drives by hard contacts. We use the small DIN rail terminal type relays. I haven't had a failure that suggested that gold contacts were necessary. The RS485 communication is used for speed command and monitoring. For our conveyor systems we sequence the turn on and turn off with delays.

So what the advantage when we start/stop drives by hard contact ? If I start/stop by RS485, will it cause system anything in later ??

If I start/stop/speed drives independent with RS485, will it cause anything ?

With hard wire stopping will be faster and safer. I´m in favor of hardwire instead of msg.

I don't see no reason why you can't start them by RS485 network. When I have many drives, I always do it by the network and don't waste PLC I/O's. One thing I always do for safety, is to hardwire the emergency stop to each drive.

we used to start / stop drives using rs485.
then the line got cut and the drive kept running.
we also had a contact on the drive go bad and the drive kept running.

we now use contactors in front of the drive tied into the e-stop and relays to start / stop the drive.

regards,
james

The key is, you need some hardwire safety at a minimum. It is common to both drop the power to the drive as well as the enable signal to a drive on an estop. The former severs the device from incoming power, the later should get things stopped quicker since many drives have a charged bus that can still continue to keep things chugging for some time after. Most newer drives have what is called STO (safe torque off) that makes this more fail safe.

Some other drives also have fault modes that allow you to configure the action to be taken if communication is lost. Unfortunately I have not seen this with modbus on anything I have used (assuing you are using modbus here).