hboyer90

How to protect output module from coils going bad.

11 posts in this topic

Hello we are running a CompactLogix setup on a few of our machines and we have multiple 120VAC coils for different valves. We control them with a 1769-OW16. Twice in the past 3 months we have had one of the coils go bad and short out, something that is fairly common as the coils get worn out. When this happens it also shorts out the output on the 1769-OW16. My question is what do you guys recommend we do to protect the module? Put a fuse or a breaker inline with each coil? I'm surprised that there isn't any type of protection built into the module itself. Thanks

Share this post


Link to post
Share on other sites
that is a relay output card. relays can be used for both AC and DC circuits but... cannot switch fast, are pricey, relays take up a lot of room (so no fuses etc). there are other types of cards too (like OA16) but selection is driven by application (type of load) - something you did not mention at all. now you mention that COILS get worn out... how did you determine that? normally contact of relay gets stressed and burns out or welds. if that is the case you need to consider type of load and proper suppression (for inductive loads) or using interposing relays. overcurrent protection (fuse/breaker) is suitable protection when overcurrent is the issue. inductive loads produce kickback which is voltage spike and fuse/breaker is not going to notice this at all.

Share this post


Link to post
Share on other sites
I did a current draw just now, the coils pull about 600mA pretty consistently while energize, it spiked up to 700mA when it first energized. When I say that the coils go bad/ware out I guess what I mean is that the core tube on the valve can start sticking over time and it causes the coil to work harder or if it gets stuck and the coil just sits there energized without the core tube inside of it then it will get very hot very fast and it will literally melt and break apart. It's a 120VAC coil with about 12ish ohms of resistance and I got a reading of about 600mA-700mA with a clamp-on amp meter.

Share this post


Link to post
Share on other sites
Interposing relays to safe the output module (with surge protection on this interposing relay) and also surge protection on the load controlled by the new interposing relay to protect its contacts.

Share this post


Link to post
Share on other sites
Im assuming by "Interposing Relays" you are referring to using the OW16 to energize another relay to control the load..??

Share this post


Link to post
Share on other sites
Yes, but you still need (should have) surge protection across the interposing relay to protect the output card.

Share this post


Link to post
Share on other sites

i am facing similar situation. i got 3 bad 1769 OW16 output cards in matter of just 2 months. upon inspection of the output card i found that the Relay contact were Welded. 1769 OW16 is Energizing solenoid coil. I am energizing total 24 Solenoid coil so consuming total 24 output points from two 1769 OW16 output card. now if i go ahead and try to install interposing relays between output card and Solenoid coils then i will have to use total of 24 interposing relays. now the catch is there is not much space to install 24 interposing relays in the cabinet. 

 

So is there any other option other then using interposing relays? or Is there any other Heavy duty relay output card which can be used as replacement for the 1769 OW16.

   

Share this post


Link to post
Share on other sites

well... what is your exact situation... OW16 is quite a beast when it comes to output cards, it handles up to 2.5A per point which is above average. most outputs are rated for 0.5A or so. if the cards fail after such short period and - so often, something is seriously wrong. i would have a chat with designer to find out what ware his selection criteria and what exactly was taken into consideration. good designed system will easily last 10+ years and - without being spared or pampered.

so... what is the voltage? how much current per point? what is the type of load? (inductive?) are your outputs rated for those loads? are you using suppression? is it a right type for that circuit and load size?

 

Share this post


Link to post
Share on other sites

panic mode,

i am using a solenoid valves and their coils are directly energized by the 1769 OW16 output cards individual points. The Output Card is Having 24 V DC supply on the VDC/VAC terminal on the Output Module. The Solenoid valves have rating of 24 V dc and 1.3 A on it. As my outputs are solenoid valves i believe the Load is Inductive.

Share this post


Link to post
Share on other sites

you are correct, they are inductive... without proper suppression device, this current will destroy any relay. sizing up will give longer life but suppression devices are far cheaper, smaller and lower cost than any relay you would be happy with.

even with suppression devices, those cards are probably doomed. you have 24 out of 32 outputs connected to loads that draw 1.3A each.

card has 8 outputs per common and maximum current for common is only 8A, not 8x 2.5A = 20A.

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now