1769-OB32 use fuses or interposing relays

[LMBrian]

Just wondering what other folks have used on their digital output loads when using this digital output module. There will be a number of solenoids, lamps and contactor coils. I have used slim interposing relays in the past as a point of isolation but just curious what others have done with this module type?

 

[PLCDontUQuitOnMe]

Just wondering what other folks have used on their digital output loads when using this digital output module. There will be a number of solenoids, lamps and contactor coils. I have used slim interposing relays in the past as a point of isolation but just curious what others have done with this module type?

Depends on the size and type of load. Can the OB32 handle both the running and inrush current of the inductive load you are attaching (you mention 3 types of loads which are all inductive).


If the OB32 can handle the load, since it is inductive you should put a flyback/snubber diode in reverse bias at the load.



If the load is too great for a point on the OB32 card, then use a relay in between. Again I'd put a snubber diode somewhere on the load side of the relay to prevent arcing.

 

[LMBrian]

Yes, I'll certainly consider those snubber diodes too!

Thank you

 

[Rson]

I always use slim terminal block relays on the outputs with the diode built in.



Something like this


It ends up being cheaper than a relay output card in the end because you don't have to replace the whole card to fix 1 relay. Just replace the single relay slice.


I usually include them on all spares as well. If one of your relays 'dies' you can have someone in the field swap a spare over and you don't have to do any programming to swap the outputs to a spare.

 

[mylespetro]

I always use slim terminal block relays on the outputs with the diode built in.



Something like this


It ends up being cheaper than a relay output card in the end because you don't have to replace the whole card to fix 1 relay. Just replace the single relay slice.


I usually include them on all spares as well. If one of your relays 'dies' you can have someone in the field swap a spare over and you don't have to do any programming to swap the outputs to a spare.

This is the ideal answer in my opinion, much cheaper to swap out one of these than a whole card, although the trick is to have some spare relays on hand. Next best option would be a fuse.

 

[TheWaterboy]

Same here, always an interposing relay.