1746-OW16 repairing and/or upgrade?

TheCaptain2000

Lifetime Supporting Member
Join Date
May 2004
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Georgia
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One of my SLC 500 AB PLCs has (2) 1746-OW16 output modules. Each of these hard contact relays "contact" every 4 seconds for 24/7/365 at 110 VAC. These relays also have a tendency to fail and warrant replacement. My company has been replacing these individual relays every month or so for the past several years. Is there a "solid-state" upgrade for these relays or another module that would work better for my particular cycling time? Is it also possible that I may be having other problems contributing to these failing relays?
 
Check into a 1746-OA16, this part number is for a 120V triac output card (solid state). Depending on the current requirements for each output, this might be the way to go.

How much current load are the outputs seeing?
 
Another way is to use 1746-OB16 and feed some standalone relay blocks with pluggable optorelays, something like Phoenix varioface.
Most mechanical relays only have a life of 10 million operations, at 4 secs cycle that comes up real quick.
I never drive anything direct from PLC output modules, always use relays and fuse between OP and device.
Boards similar to AD Ziplink, saves many headaches when field devices have a problem.
 
Do you have surge protection across your Outputs.

Most manufactures recomend using a surge supressing device across all inductive loads swiched on by PLCs.

I am not 100% if doing this is effective or not, or if it is cash grab by the supplyers. I would be interested on what others think of putting the diodes across the coils.
 
I have been looking into that particular module. One of my other machines (not same type of machine) has these OA16s in it along with smaller diameter wire when compared to my OW16s. However, I am not currently not sure of the current draw of the outputs of either machine. What are my restrictions? By what I can tell, the OA16 may not be able to handle as much current as the OW16, which may be going in the wrong direction.
 
Your definetly right Capitain, If you are going through OW16 cards you will definitly be going through OA16 cards at a faster rate. This will not be a solution for you but a bigger head ache.
But hey I have been wrong before.
 
I am going to investigate the possibility towards going to the AW16s with optorelays. If using the standalone relays, the current draw from the PLC will then almost be negligible compared to the full load draw it is currently taking. Perhaps even running the OW16s with the same relays can be considered if the load on the AW16s are still to much. Please continue to post ideas to this thread as I always like other options.
 
one more thing that hasn't been mentioned yet ...

before you switch from "relay" to "solid state" type output modules, be sure to consider the "leakage current" issue ... sometimes this is THE reason that the original design uses the relay types ...

basic idea: the solid state outputs on a 1746-OA16 module do not really "GO OPEN" when the output is switched off ... instead the output just shifts to a very high resistance ... and so there is still a small amount of "leakage current" which can continue to flow in the "TURNED OFF" output circuit ...

some applications can tolerate this "leakage current" with no problem ... in other applications it can be a serious issue ... so what type of outputs are you driving anyway? ... if you're thinking of using "interposing" relays (especially the solid state type) downstream of the PLC output module, make sure that the relays can tolerate this leakage current at their intputs and still function correctly ... some can ... some can't ...

final thought: IF (big IF) the current draw is within the specs, the 1746-OA16 modules usually last much longer than the 1746-OW16 modules ... that's because the solid state design has no moving parts and no physical contacts to arc and spark when turning on and off ...
 
Last edited:
Allan Barnes said:
Your definetly right Capitain, If you are going through OW16 cards you will definitly be going through OA16 cards at a faster rate. This will not be a solution for you but a bigger head ache.
But hey I have been wrong before.



Ron Beaufort said:
If the current draw is within the specs, the 1746-OA16 modules usually last much longer than the 1746-OW16 modules ... that's because the solid state design has no moving parts and no physical contacts to arc and spark when turning on and off ...

Thanks Ron, That was my point.
 
Well, I just got back from the warehouse and took some readings. Most of my outputs from my existing OW16s are no more than 1A at 110VAC.

BTW, this PLC is driving a Cincinatti Millacron Blow Mold Machine (RHB). There are only about 5 out of my 32 output relays that fail almost weekly. Once again, they do run ALL THE TIME in 4 second cycles. I know that just mechanical motion alone is wearsome, by my numbers indicate that these relays are cycling about 151,000 cycles a week. How much life can I really expect for a relay like that has a 1 amp draw on it at 110 VAC?
 
before you switch from "relay" to "solid state" type output modules, be sure to consider the "leakage current" issue ... sometimes this is THE reason that the original design uses the relay types ...

We are currently looking at changing out our OA16 modules for the OW16 modules, because some of our opto card relays are sensitive to the leakage current when combined with some other problem(such as a slightly oscillating power supply, etc.) We were getting "ghost" cycle signals that our servodrives would pick up on sometimes. We are looking at fixing our outstanding grounding issues, etc., but with just that one change, one of our problem machines stopped having problems.....
 
TheCaptain2000 said:
There are only about 5 out of my 32 output relays that fail almost weekly. Once again, they do run ALL THE TIME in 4 second cycles. I know that just mechanical motion alone is wearsome, by my numbers indicate that these relays are cycling about 151,000 cycles a week. How much life can I really expect for a relay like that has a 1 amp draw on it at 110 VAC?

I would expect relays to last MUCH longer than that. These outputs are driving solenoid valves, right?

Are there supressors (TVS, MOV) on the coils?

Are they still there?... utoh

beerchug

-Eric
 
two other ideas

Since the current is clearly inside the spec limit of an OW16,
the problem is NOT steady state current. The problem is clearly
in the duty-cycle, and the transitions from on to off, etc.

And, since only some of the outputs are failing, and they are
all on this cycle thing, why not fix THE problem.

I'd suggest the following:
ALTEC (and others..GORDOS/OPTO) make a 4 and 8 channel
solid state relay rack. Mount enough solid state relays to
cover the high cycle outputs, mount and wire the thing, and
move on with your life.

Of course, the ALTEC/GORDOS/OPTO module will have to be
driven by a DC output, but, that should not be a problem,
assuming you have access to the program, etc.

You say that they are on/off every 4 seconds. Why not buy
a recycling timer (NCC/DIVERSIFIED/P&B) that makes that output,
and simply turn on and off that timer with the existing PLC
output. Again, I'm assuming you have the space. (You
certainly have the $$$, if you can keep replacing the
output cards)

NEW TOPIC:
What is the opinion of others...should the original installer
be held accountable for what is clearly a poor electrical design?
 
Re: NEW TOPIC

jdbrandt said:
NEW TOPIC:
What is the opinion of others...should the original installer
be held accountable for what is clearly a poor electrical design?

Yes, but you don't know Cincinnati. We had a few of their injection molding machines at my previous employer. Trust me, electrical reliability was not their strong point... :rolleyes:

I say WAS, because hopefully, their new stuff might be better?... :confused:

beerchug

-Eric
 

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