wiring PLC digital outputs to VFD

I am studying this AB 160SSC VFD. I have attached a picture from online manual of this VFD. It shows wiring method IF I used regular PBs and toggle switch. Since terminal 7 is "common," I figured 5, 6, and 8 are V+. Am I correct so far?

My PLC (micrologix1000) output terminals have VAC and output terminals but no COM terminal. So, the only way to wire it is to wire VFD's #7 terminal which is COM to VAC, (and each PLC output terminal to 5, 6, and 8, which doesn't make sense.

help please.

thanks.

unsaint32 said:

My PLC (micrologix1000) output terminals have VAC and output terminals

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What is the model number? If it is only labeled VAC, then I'm guessing it's a 1761-L32AAA? That model has triac outputs (except outputs 0 and 1), and triacs cannot be directly wired to a VFD. You would need to use interposing relays. Relays get turned on by the PLC, and the relays' contacts connect to the VFD.



-Eric

As the manual states,the drive has an internal 12V power supply. You may want to use interposing relay(s). Use your output to fire the relay, use the relay contacts in place of the PBs.

Sorry for the duplicate reply, Eric beat me to it, I'm trying to type with a two year old jumping on me.

Use an interposing relay and locate it in the drive's enclosure, if possible, to avoid routing the low voltage DC wiring back to your PLC enclosure.

Using three relays makes sense. But I am going to go home and try wiring the way I had explained in my original posting. I know it doesn't make sense to wire the PLC's output VAC terminal to VFD's COM terminal. But someone at work told me it would work. I will let you know the outcome. Thanks for all your help.

unsaint32 said:

Using three relays makes sense. But I am going to go home and try wiring the way I had explained in my original posting. I know it doesn't make sense to wire the PLC's output VAC terminal to VFD's COM terminal. But someone at work told me it would work. I will let you know the outcome. Thanks for all your help.

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Try to avoid breathing in the smoke when you do this...

The triac outputs of the PLC, are not meant to switch Low voltage DC. Even if it did happen to work, I would not trust it for operation.

If your PLC is AWA or BWA, then your common on the PLC will be VAC/VDC. This is a relay output (dry contact), you just cannot connect anything else to an output going to the same VAC/DC

The schematic you're showing above is using a power loop that is internal to the drive. You'll need to use relays off your outputs in order to do this properly. There may be a way to use external power for the drive IO, but I haven't seen a 160 for a little while.

Using three relays makes sense. But I am going to go home and try wiring the way I had explained in my original posting. I know it doesn't make sense to wire the PLC's output VAC terminal to VFD's COM terminal. But someone at work told me it would work. I will let you know the outcome. Thanks for all your help.

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I could see this working potentially. Are you sure the VAC terminal doesn't say something like "VAC-VDC"? Basically, if you have a PLC with relay outputs, then yes you'd essentially be using the VFD's internal voltage as a common signal and the contact closure on the internal relays in the PLC to do the same thing as external interposing relays. If it has triac outputs, the results are a bit more unpredictable. Triacs still put out voltage even when they're off. A substantial amount, in fact. And putting DC voltage on triacs designed for AC...I don't know.. Without knowing the exact model Micrologix you're using, nobody can really say.

But I am going to go home and try wiring the way I had explained in my original posting.

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Wait! First let me take out a fire insurance policy on your home. I could use a few thousand extra this month....

PS: Can I have the old VFD, once you burn out the 12 Volt input circuit?

Don't accept the words of the men who have wired up a thousand. Instead read the warning in the manual.

If your VFD is a Catalog No. 160-DM-SF1 (Analog), or a 160-DM-PS1 (Preset), then it may have a 24V DC Interface Module. In which case you might carefully wire its Input terminals to the PLC Outputs of certain models of the MicroLogix1000. It all depends.

unsaint32 said:

I am studying this AB 160SSC VFD. I have attached a picture from online manual of this VFD. It shows wiring method IF I used regular PBs and toggle switch. Since terminal 7 is "common," I figured 5, 6, and 8 are V+. Am I correct so far?

Click to expand...

No. You are not correct, so far. Terminals 5, 6 and 8 are current sinking DC inputs.

unsaint32 said:

My PLC (micrologix1000) output terminals have VAC and output terminals but no COM terminal. So, the only way to wire it is to wire VFD's #7 terminal which is COM to VAC, (and each PLC output terminal to 5, 6, and 8, which doesn't make sense.

Click to expand...

It doesn't make sense because it is wrong. Why ask for help if your intention is to simply ignore the advice that you are offered?

Eric Nelson said:

What is the model number?

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Still waiting...



-Eric

Still waiting...

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Unsaint was very busy today. First there was the fire department, then the insurance adjuster, then the wife and kids wanting to know where they were going to sleep tonight!

Guys I don't think he was necessarily intending to use an external power supply on the drive terminals. I think he was doing something like this

7          VAC

X----------X

           OUT0          5

           X-----------X

Terminals 7 and 5 are on the drive, VAC and OUT0 on the PLC.

Where the 12 Volt DC Power from the drive would provide the FEED for the outputs themselves, and go back to the drive, closing the loop. If his controller has relay outputs, I'm pretty sure this could work. But if he's using Triac, I couldn't say what would happen, especially on outputs designed for AC voltage only.

Sure, you can use relay outputs to connect directly to the drive, but I wouldn't recommend it. In the case of this particular drive, you would suffer from significant voltage drop with the standard 12 VDC power supply if your wiring exceeded a length of 50 feet. Besides, it's just a bad idea to expose this low voltage wiring to the electrical noise that routing it into an I/O panel would likely entail.

You'd only need 1 interposing relay to run the drive forward, and 2 relays if you want forward and reverse operation.

Sounded like the OP was just hooking it up temporarily to experiment, but yes, if you were designing something permanent, separate relays are the way to go.