motor runs backwards a sec??

[plcnewbie]

I have a motor that runs an overflow and it comes on only for a second now then it runs backwards for a second. Does anyone have any idea what could do this?

Thanks

 

[MrQ]

Maybe you are missing one of the three phases.

 

[mrm37]

is it an A/C or dc motor?

 

[Tom Jenkins]

What is the motor connected to? An overflow to me implies a port or pipe that allows a fluid to run out by gravity - see the back of your toilet tank. I've never seen a motor operted "overflow".

Is this acutally a pump? In that case, after the motor stops, the fluid in the pipe could run backwards and turn the pump into a turbine.

You need to provide a lot more info to solve this one.

 

[plcnewbie]

Sorry it is an ac 3 phase motor. Dont know if I am missing a phase or not I would say not cause it was installed by "pros" but I could check but am not sure how just yet.

 

[plcnewbie]

Sorry Tom I know better than this. I have been reading this site awhile now and was just in a rush.
Anyways when I say overflow I mean product overflow as in the main conveyor is backed up and the product has to get off of someother equipment such as diverter and needs someplace to go. So it is called the overflow lane.
It was recently reconfigured but am told by maint. that it was running good during practice run. It looks to me like it could be binding up and causing an overcurrent cause the drive keeps giving me fault 7 or overcurrent fault. I was runnning slow at like 6hz and pushed on it and it didnt budge but then let go and it moved back like half a foot. It was moving fwd during activation 6 inches aprox then back.
I hope this helps and as the name implies and obviously the question I am still a PLC newbie and appreciate this site very much.

 

[Werner]

I have had a motor which also turned backward for about 1 second. This was because of tension in the belt pulling the motor backward. Without the load (belt) connected to the motor it did not move backward.

 

[JesperMP]

Some ideas:

It is an inclining conveyor, and the material on the conveyor drags the conveyor in reverse direction when the motor isnt driving it.

Or, the conveyor it is a rubber belt, and it is relatively long, and it is so heavily loaded by material that tension can build up in it thereby stretching the belt. The stretch is released the moment the motor isnt driving it. The release of the stretch drives the motor in reverse but doesnt move the belt.

Or, the setpoint for the VFD is provided by voltage or a potentiometer. And there is a small error at the zero point (= 0 Hz) so that a small negative setpoint is applied, commanding the VFD to drive it backwards when it should stop. The driving force is so little at the small speed that the belt eventually stops by friction.

 

[plcnewbie]

Sorry Jesper none of the above so far

I pulled up both drives in drive executive and they look god to me. I can force it on via toggle of a bit and it comes up to the desired speed then back to 0. If I latch it on in the program the speed only goes to 6hz and it doesnt move. But normal speed is 18 hz.

All the currents and voltages checkout via drive exec and the overcurrent param is at 4Amps.
Surely with all this knowledge base here someone has the answer for me...

 

[Seagullplayer]

How are you "telling" the drive to start, and what speed selection to run? Are you using hardwire contacts? If so, perhaps your selecting the wrong speed? Maybe even reverse...
(What type model drive?)

Sorry Jesper none of the above so far

I pulled up both drives in drive executive and they look god to me. I can force it on via toggle of a bit and it comes up to the desired speed then back to 0. If I latch it on in the program the speed only goes to 6hz and it doesnt move. But normal speed is 18 hz.

All the currents and voltages checkout via drive exec and the overcurrent param is at 4Amps.
Surely with all this knowledge base here someone has the answer for me...

 

[plcnewbie]

the drive is given a command to start for a short period of time based on a backup eye becoming active so it comes on for a short time then off I am doing a toggle on this bit in the monitor screen.
By the way I am using a pflex40 and CLX5000

 

[Tom Jenkins]

Try enabling the DC Injection Braking, and see if this corrects the backspin.

 

[plcnewbie]

Tom, This is what gets me, I pull up 2 of the same drives in drive exec and both are essentially overflow. One for metal contaminates and one for non metal overflow. They are exact to the T.

I dont know maybe I am missing something here?
If I enable the DC wont that demagnetize the motor?

 

[Tom Jenkins]

I pull up 2 of the same drives in drive exec and both are essentially overflow

Do you mean you get an "overflow fault" in the VFD? Could this be a code for overvoltage trip? Is the fault code "OF"? Check you manual. It is common to get an overvoltage fault if you try to decelerate an over running load too quickly.

If I enable the DC wont that demagnetize the motor?

No - DC injection braking essentially uses a little DC voltage when the motor drops to a low speed (like 1 or 2 Hz) to bring it to a full stop.

 

[plcnewbie]

when I say both are overflow I mean both are overflow lanes and are programmed the same. Problem could be elsewhere since we do have more than a couple tech and some dont always document all the changes they make and we are in the process of installing new equipment. So who know? I am going to go beat my head on the floor awhile longer.


Thanks so far I will update.