Allen Bradley's remote I/O module


Thread Starter

David McAnally

We are using a Allen Bradley 1791OA32 remote output module. I am about to replace the fourth module in an application that is less than two years old. All of the outputs are properly fused.

Sometimes the entire module goes out and at other times a single output will fail, follow by another output a few weeks later.

James Ingraham

We have many of these blocks that have been in the field for 5+ years with no problems.

The occaisions we have had blocks go bad have almost always been a result of an inductive load, e.g. a solenoid valve.

-James Ingraham
Sage Automation, Inc.
If your outputs are driving solenoids or other inductive loads you may need to place an MOV across the load. I have seen a similar problem with the Micrologix series for it's outputs. Also, that output is limited to a max current of .15 - .6A, depending on mounting orientation and ambient temp.


Steve Myres, PE

I agree with the posters who suspected an inductive load, like a solenoid with a massive coil, or a large contactor. Another idea, in lieu of snubbing the load, would be to interpose a small ice cube relay between the output and the load. They will draw about 1 watt, and can probably drive a much larger load than the solid state output. Also, if they do eventually fail, they cost $5 and take two seconds to replace.

Anthony Kerstens

Is there a device connected to it that draws more current the what can be handled?? Are there any short circuits??
Just a note of caution on inductive kickback and coil size:

The magnitude of the transient signal is not related to physical sized. Small, 1.5 Watt, AC or DC, "cube-size" relays can generate up to 1,500 volts if not equipped with transient suppressors... even if hermetically-sealed!

Regards, Phil Corso, PE (Boca Raton, FL) [[email protected]] {[email protected]}