Simple VFD control question

[fast904]

Hello,

I am looking to design a simple control system with a few controls and I believe I might be able to control it entirely with an Eaton DG1 drive.

I will have two motors being controlled - one through the VFD lines, and one through the VFD I/O. I will be shutting off a starter through the VFD I/O based on a limit switch.

There is a liquid tank with a digital switch to sense an empty tank condition, and a small motor inside the tank that needs to remain ON for an additional 10 seconds after the empty condition is sensed.

I would like to send a digital input signal from that switch to the drive for the empty signal, and send a relay output with time delay to the coil on the contactor so that the smaller motor remains on for 10 seconds.

I would like to use a normally closed relay after the three wire control on the small motor control circuit. When the signal hits the relay it should open the contactor, and the sealing contact, and then kill off the circuit until the button is pressed again.

Does this make sense? I appreciate the help!

DG1 comes with I. Eight (8), 24VDC digital input as standard
ii. One (1), open collector 24VDC digital output
iii. Two (2) 4 to 20mA analog inputs
iv. Two (2) 4 to 20 mA analog outputs
v. Three (3) dry relay contacts rated for 250VAC at 2A or 250VDC at 0.4mA

 

[osmanmom]

Post your layout diagram or electrical diagram

 

[jraef]

You dont say what the VFD s doing, pumping up or pumping down? And how does that coincide with your statement about the other motor having 3wire control? So yes, a diagram from you is a better place to start.

Small inexpensive component class drives like that do not typically come with time delay programmability on the output relays, but you can do that with one simple external timer.

I'm not sure about the "normally closed relay after the three wire control on the small motor circuit" issue. I think maybe you are attempting to recreate what is typically done with an "Off Delay" timer (NOTO). That's really all you need here. An Off Delay timer, sometimes called Normally Open, Timed Open (NOTO) means that a contact is open until you energize the timer coil, at which time it instantly closes. Then when you de-energize the coil, the contact remains closed for the time setting and re-opens after the timer times out. You would use that as your control relay to the motor starter coil, and however you start that auxiliary motor goes to the timer coil, not the motor starter. So if it is a 3 wire control scheme, the Start goes to the timer coil, the seal-in around the Start is an untimed contact of the timer (meaning you have a timer with 1 instant + 1 timed contacts). But for this to work right, you must make sure the Stop button is ONLY on the timer coil side. Then you take another NOTO contact of the timer and go directly to the starter coil. If you look around, there are even a few motor starter mfrs who offer a snap-on timer head that goes directly on top of the starter itself that can do this.

You press the Start, it energizes the timer, the contacts close, the timer seals itself in and stays that way, the other timed contact closes immediately and energizes the starter coil, the motor runs.You press Stop, the timer coil de-energizes, but the timed contact in the Starter coil remains closed, keeping the motor starter energized, until the time expires. Then it opens and requires a new Start command..

 

[fast904]

Thanks for the replies all! Yes, that NOTO relay was my original thought for the application, and would save the trouble of programming the drive. I was trying to find out if the time delay/VFD controlling contactor was possible, and also save money over having a more expensive timer relay vs. a simpler relay.

The VFD does have a time delay function on the relay output, so I think I should be able to achieve that. Up to 320 seconds.

Below is what I was hoping to achieve, just in concept. The other larger motor that the VFD controls is actually irrelevant to the question, I think.

 

[ROAMER_AUS]

I dont know the mentioed drive in details. Bit I just wanted to show support for what you are doing. I am a big fan od developing projects with minimal amount of equipment and complexity involved. I used to make automatic saws with automatic blade speed and blade on cutting metal pressure using only 2 eurotherm drives and proud of it!

Id probably get time delay relay if your dive doesn't offer that option. It will be cheaper than getting different drive anyway.

Hope it works for you!

 

[fast904]

Thanks for the support Roamer! Your project sounds cool too. My end goal is to save money so I'll have to compare the cost of this drive to the cheaper options without the fancy programmability. The drive I'd like to use actually includes DC bus choke too to clean up harmonics.

 

[Lancie1]

Yes, that NOTO relay was my original thought for the application, and would save the trouble of programming the drive.

It also saves the trouble caused by the two systems from being tied together permanently. What happens if the VFD fails, and no one knows that the large motor logic depends on the small-motor VFD timer? A dedicated Off-delay timer for the large motor means its function is not dependent on the VFD for a different motor.