Allen Bradley PLC5

Hello,
We use 4 racks with 1785-L80B, 1785-BCM and 1785-BEM in them. I am looking to purchase secondhand a few spares as we have had some problems recently as they are now very old.

In AB data sheet the difference between a 1785-L80B and a 1785-L60B is in the User Memory Words Max. Everything else looks the same. I was thinking of trying a 1785-L60B in place of the L80B. What problems might I encounter ?

The ladder logic program that is uploaded from RSLogix is about 2.2 MB for 2 of the Racks and for the other 2 about 1.2 MB.

The other problem we are having is with the 1785 BCM and BEM modules failing. These seem to be very fragile. When I switch off a rack I switch it to program mode first however this does not seem to help. We did this last week and when we switched on again two modules failed. The racks are power fed of industrial UPS system. We are now in the situation of not wanting to switch anything off in case it fails.

Any help appreciated

Thanks

Dave

The ladder logic program that is uploaded from RSLogix is about 2.2 MB for 2 of the Racks and for the other 2 about 1.2 MB

Click to expand...

These numbers are most likely the size of the .RSP file ( RSLogix5 program file). Not controller memory.

If you want to know the memory usage of your PLC's then open the RSLogix project and look under "Controller Properites" See picture

I have never used your backup modules so no comment from me there.

Welcome Dave,

Open your PLC file offline and try to change the processor to a 1785-L60B under "controller properties" and the program will tell you if you can save it with that controller.

I tried it with mine, but I do not have the L60B/L80B options.....

Thanks both for the info. I checked this morning as suggested and on 2 of our racks the spare memory went negative when I tried to use a L60B. There is little spare with an L80B in use so definitely need to keep these 2 as L80B.

On the other 2 racks it worked fine and on another rack (forgot to include yesterday) it also worked OK. So I will try and purchase a spare L60B to experiment with.

If anybody has experience or knows anything about the 1785-BEM or 1785-BCM then please get in touch. Another question about these. If I ran out of these modules could I just not use them and use a single L80B on its own to drive our system ? Yes if it was to fail then I have a problem but so far none have failed in 20 years. Would I have to modify the loaded .RSP file to get this to work ?

The 5th rack only has a single L80B and a panel view and when put in use can control part of our system manually.

Thanks

Dave

I have lots of the BCM & BEM modules in use where I work. They can be reliable but they can also be a pain. I have found them causing "lock ups" of the entire DH+ network.
In reply to your question "If I ran out of these modules could I just not use them and use a single L80B on its own to drive our system ?" You can indeed. If wired correctly it should just be a case of turning off on of the processors completely. The other processor will sit there permanently as PRIM.