Hi guys

I want to replace a 3 phase contactor that is running a small motor pump with an inverter drive. The pump is simply run from a stop and start push button and a start stop control from a HMI screen. The contactor coil is just being switched on and off directly with the start stop buttons and the HMI and there is a small auxillary contact on the front which IS using one side on the NO contacts to link to 2 other contacts. So in short i just want to replace the contactor with the inverter. Attached below is link to inverter i am using, but I am a little unsure where to wire the signals back to as i only have the A1 signal from the contactor coil to work with. the Inverter terminals 1 2 and 4 seem to be controlling the operation but im not sue what else i need.

Thanks


https://ie.rs-online.com/web/p/products/0447553/

 

Don't know about that inverter, which seems to be what is normally called a VFD. But some that I'm using on my machine tools can be selected in the actual VFD menu to use different means of control. It will tell you in the units 'operation manual' how to do it, if it can be done.

 

As per @shortbus Do you have the instruction manual, it should show how to hook up a simple contact closure to the PLC input terminals of the Inverter.
Many have the option of a sink or source type contact and is powered from the PLC itself.
Do you have a link to the actual installation manual?
Max.

 

A general Powerflex manual is out there and it shows all the simple inputs possible for control in the wiring section.
The simplest way may be to use a small aux relay and just use a contact for stop/start.
Max.

 

I want to replace a 3 phase contactor that is running a small motor pump with an inverter drive. The pump is simply run from a stop and start push button and a start stop control from a HMI screen. The contactor coil is just being switched on and off directly with the start stop buttons and the HMI and there is a small auxillary contact on the front which IS using one side on the NO contacts to link to 2 other contacts. So in short i just want to replace the contactor with the inverter.

The bigger issue is why do you want to switch them out to begin with? What do you think the VFD unit will accomplish that is superior/advantageous over the on/off contactor control?

Pumps have non linear pressure/flow outputs for changes in motor speeds which means it takes very little motor speed change to drastically change the pressure and or flow characteristics to the point they may either damage the pump due to unforeseen deadheading or overload the motor due to excessive pressure/flow output.

Switching the contactor over to the VFD unit is the easy part, Setting it up to reliably and correctly run the pump many not be.

 

Yes, you can. There are digital inputs on the inverter that can be connected t external stop and start buttons. You will probably have to set parameters to enable these instead of the buttons on the front panel. The quick start gude on the RS website shows the connections.

Best thing is to simply re-wire your buttons direct to the inverter. If you want to use the original A1/A2 wires you will need a small isolating relay.

Of course the inverter has a lot of advantages over a simple contactor:-

• Electronic overload protection
• Speed control
• Pre-set acceleration and deceleration

 

Are you sure that the pump (Assuming it is a normal 50 / 60 Hz motor.) will work from the output of the 400 Hz inverter in your link ?

Les.

 

Hi guys

Thanks for the info. I want to put an inverter on it purely to speed the pump up a small bit as it is currently running too slow. I chose the inverter (even though it is not purchased yet) because this particular type is in use on all the other motors in the plant and i just want to keep everything as generic as possible.

 

As per post #4 just use a small aux relay in place of the contactor coil, a N.O. contact to the VFD.
Max.

 

Excellent guys thanks a lot much appreciated

 

I want to put an inverter on it purely to speed the pump up a small bit as it is currently running too slow.

If it was built to run at the line frequency it is connected to then you are likely going to have problems with it by trying to run it faster than it was designed to run. It relates to the very narrow band of pressure/flow rate curves that the specified motor can handle without being overloaded and eventually burning up.

Unless you're trying to compensate for having a 60 Hz rated pump on a 50 Hz power source there's a very high likelihood that speeding it up over its stock design rating will overload the motor to the point it either overheats and shuts off (if it has built in thermal protection) or totally burns up.

Just something to consider.

 

Are you sure that the pump (Assuming it is a normal 50 / 60 Hz motor.) will work from the output of the 400 Hz inverter in your link ?

Les.

400Hz is the max, which you can obtain by changing parameters. Default is 60hz max.

 

You should be able to do a 1-for-1 swap without adding any relays by doing a 3-wire setup on the PF4/40. I haven't set one of these up in a long time but IIRC if you change this parameter it initializes the drive and wipes out all the other parameters- that might be a different MFG drive, I might be wrong. But just to be safe, change the start source parameter 36 FIRST. Then do your tuning and set up your other parameters.



Edit:
You can leave out the direction switch shown in the diagram. You don't need it.

 

Also looks like you can use simple 2 wire.
Also if needed, you can set 2 or more pre-set speeds, input switch/relay selectable.
Max.

 

Hi guys

Just going back to the panel now and i have realisied that the contactor is 115vac where as the inverter will only take 24v control signal. I was just going to take a feed from the auxillary and run it to the inverter as per your recomandation Max but now i cannot due to the voltage difference

 

The inverter will probably just need to see a set of contacts close to enable it's output so just use a relay with a 115 volt coil.

Les.

 

The

Just going back to the panel now and i have realisied that the contactor is 115vac where as the inverter will only take 24v control signal.

The signal on the VFD PLC input will be isolated via the simple contact closure, IOW the VFD/PLC input has its own 24vdc supply internal.
Max.

 

but if i use a 115vac relay to activate the run signal is that still not putting 115vac into the inverter?

 

but if i use a 115vac relay to activate the run signal is that still not putting 115vac into the inverter?

You will just be using a N.O. contact on the relay, this does NOT have any voltage present on the contact, it is just contact closure, it just switches the input to the common terminal of the VFD input.
The 115vac will just be fed to the Coil of the relay and is isolated from the contact..
Max.
typical relay.

 

but if i use a 115vac relay to activate the run signal is that still not putting 115vac into the inverter?

The 115vac is the control coil rating.
It is unrelated to the voltage switched by the relay contacts, which can be the same or a different AC/DC voltage, as the contacts are isolated from the coil.