1794-ow8 application

[corollace]

In my plant, we are using lots of 1794-ow8 with 120VAC output application. but some of them output point, when there is no output from PLC, but I can get 115VAC output to the solenoid and solenoid would not be energized. when we have output OTE, the output point would be 120VAC and energize solenoid. what is the problem, and i always got fuse blew out.

thanks

 

[Lancie1]

Corollace,

I am not clear about your problem. Are you saying that some of the outputs on your 1794-OW8 module are on when they should be off?

 

[tom_stalcup]

Ehhh....

I'm not the greatest expert on this sort of thing... But...

Where are you measuring the 115 volts from? From the output card to the neutral? To a ground? On the solenoid itself? And if you disconnect a wire from the output card and take readings with nothing hooked up to that output, are the readings the same or different with the output on or off?

 

[RSL]

Since the card he mentioned is a relay card, I would suspect something is a miss in the field wiring.

Tom is taking you in the right direction. You need to check all the wiring and assume nothing. You should also ohm out the loads and see if they are good. You could also take readings at the output card itself with the loads unhooked to verify the card. If you are trying to ohm anything remember to kill the AC common to the card 1st.

It could be the card, but if it is the load might be what ruined it?

Take some readings and post the results in detail.

RSL

 

[Contr_Conn]

Just keep in mind that this is NOT a dry contact.
Circuit has snubber and resistors, that will create a leakage current if load is below the minimum.
Check minimum current first.

 

[curlyandshemp]

In my plant, we are using lots of 1794-ow8 with 120VAC output application. but some of them output point, when there is no output from PLC, but I can get 115VAC output to the solenoid and solenoid would not be energized. when we have output OTE, the output point would be 120VAC and energize solenoid. what is the problem, and i always got fuse blew out.

thanks

We had the same problem on a job site last year. Tried swapping 1794-OW8 cards, but problem persisted. Turns out we did not wire the the TB3 base the card was in correctly. Confirm that the TB2 or TB3 bases have all supply power DC+ and DC Common properly connected.

Ian

 

[RSL]

I thought the ow8 was a dry contact relay output module. However I see that it plainly lists leakage current through the snubbers in the specs. I had never noticed this or had a problem caused by it before.

Thanks Contr_Conn

RSL

 

[Contr_Conn]

I thought the ow8 was a dry contact relay output module. However I see that it plainly lists leakage current through the snubbers in the specs. I had never noticed this or had a problem caused by it before.

All OW modules from A-B (1756,1794,1771,etc) are very similar and have leakage.
The OX modules have a true dry contact.

 

[corollace]

Thank you guys reply. It's really wierd. The voltage measure on module card output to ground, some of them have, some of them not. yesterday, we got problem again, from TB2, measure 120 to ground, nothing on solenoid side, even i unhooked connection, still got 120 from the output.

I will double check the base DC wiring, it was working for a while, just suddenly happened. we are planning to change those card to DC output + relay to see if we can solve the problem.