This topic contains 9 replies, has 4 voices, and was last updated by 
Phi Bach 1 year, 3 months ago.
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I am planning to use 1762-OB8 Output card to control the VFD.
Please see attached screenshot of VFD & 1762-ob8 card and let me know answers of below question.
I will connect 24V of VFD to +VDC of 1762-OB8. I will connect LI1 to OUT1 of 1762-OB8. I am confused that where do I connect DC COM of 1762-OB8 ?
Do you want to only turn the VFD on and off or control the speed of the VFD using the MicroLogix?
Because if you want to control the speed you should have a 0-10vdc output module.
Thanks Steve,
I want to only turn VFD on & off using micrologix. Speed of conveyor will stay same.
Hi Guys,
Raj, if you have the option to use a relay card (ex. 1762-OW8) then I would recommend that as this will allow you to use the drive supplied 24 VDC to switch for example LI1. Then you would likely need to program LI1 for the drive function you want…to start the drive. Because you are using a transistor based output module you will be feeding the drive directly from the output card. I don’t recommend this, if you have no other option but to use that 1762-OB8 module I would wire the output to a small relay (an “interposing relay” that just need one N.O. contact) then use that “dry contact” to switch the drives +24 VDC to the input you want as shown in your drawing.
Hope that is clear.
I would disagree about using a relay, not that you can’t you can buts it’s not needed in this case, since the VFD allows for supplying voltage from an external source. (See attached pict)
Then you would program the VFD to turn on and off via one of the LIx inputs.
Hey Steve,
Did not look at that pic…you’re absolutely right! Should not be an issue.
No worries!
Thanks
Steve
Means I can’t use VFD internal 24Vdc if I choose to control VFD via 1762-OB8 card ? Do I need to provide external +24Vdc power supply ?
Hi Raj,
This has already been answered above and sorry for the confusion but it is very clear from the other image you provided that there is an option to drive the LIx inputs from a transistor output module (OB8) as Steve pointed out. Simply wire it as per your drawing and program the drive appropriately and you should be all set. The output itself will have +24VDC on it when you turn it on in the PLC program.
Fred
Did it work for you?
