1769-OA16 module issue

[jtashaffer]

I have a output module with only 1 output being used local 5 O data 15. Don't ask that is just the one they picked. Easy and on the bottom I guess. The output is reading voltage 119 volts AC even if the output is not on in the PLC program. Also all the outputs in this module have 120v on them. But that output is sent to a CR coil and I have voltage there to but it doesn't turn on the relay. I am sure the card is bad. I was just wondering if anyone has ran across this before.

 

[Ken Roach]

It's very ordinary to read 120 volts (nominal) on the output of a solid-state AC Output module.

The triac circuit these modules use "leaks" a few milliamperes. It's enough to turn on neon lamps, some PLC input circuits, and even some tiny relays all by itself. It's just the nature of triac circuits.

If you are reading 120 volts on the output and it's not being "sunk to ground" through the relay coil, the relay coil or a terminal somewhere between the coil and Neutral is bad.

It's possible for triacs to fail in the ON state, but that would be driving the coil of the relay. I doubt the module is actually bad.

On the bright side you could switch to an unused channel easily, right ?

 

[jtashaffer]

Every output on the card is reading 120v but none of the indicator lights are on. I changed the relay and the base just To make sure. I still got the same results. I checked the Neutral wire it was also ok , it is only 6 inch or so from where all the neutrals are tied togeather.

 

[Ken Roach]

What you're describing is normal; the output terminals can be measured at 120V AC just from the leakage through the triac, even with the indicator lights off.

Use a jumper to provide 120V to the input terminal of that relay; I'll bet you a shiny donut it doesn't pull in.

 

[Mickey]

Reread Kens post.

What you are seeing is off state leakage, its normal. see pdf.

Put a load on the output and it should go away depending on the load of course.

What is the load?

Edit: Ken types faster then I do.

 

[jtashaffer]

just a 120v relay

 

[Mickey]

just a 120v relay

Usually an inductive load is enough to pull down the voltage if the coil is big enough.

One problem is sometimes once the relay is energized then denergized the leakage current can be enough to keep the relay pulled in. You will have to test this. If that is the case then one option is to install a bigger slave relay.

Another option is to replace the solid state output module with a relay output module.

 

[jdbrandt]

Here's another idea, since it sounds like the circuit attached to OUT15 is open.
Turn all power off, and observe OSHA 1910.147.
Leaving everything connected and installed, gently remove the wire attached to OUT15, and hang it in free air.
Then, attach one lead of an ohm-meter to this OUT15 wire, and the other lead of the ohm-meter to whatever "common" is connected to the "low side" of this relay.
I'll bet another shiny donut that the ohm-meter reads "OL" (infinity)

 

[jtashaffer]

Update it was leakage current as you guys had stayed the relay wouldn't actuate the coil until the output was actually on. I am used to relay output modules so it was throwing me for a loop. Thanks for your help.