Allen-Bradley / SLC 500

Every 1747 processor and 1746 module catalogue number, with the Rockwell migration cross-reference. Discontinued, still running plant, no official supply.

The SLC 500 was the mid-range Allen-Bradley platform for two decades. It went into dairy, meat processing, water treatment, packaging and general manufacturing, and a great deal of it is still in service because it works and because migrating a running plant costs more than maintaining it.

Rockwell has discontinued the range. A failed module cannot be bought through the official channel. What exists is new old stock, surplus from decommissioned plant, and tested used modules.

1747 processors

The processor is the expensive part and the one people most often get wrong, because the trailing digits look arbitrary.

They are not. The trailing digits on every SLC 500 catalogue number refer to the user memory size in 16-bit words, not the CPU bus width. An L552 and an L553 are both 32-bit internally. The L553 simply has 64K of user memory instead of 32K.

The 1747-L542P, 1747-L543P and 1747-L553P variants also exist.

The 1747-L553 is the final user memory tier of the SLC 500 platform. There is nothing above it. If a program has outgrown an L553, the only route is migration.

Which communications does yours have?

This is often what actually decides the replacement. A 5/04 on DH+ and a 5/05 on Ethernet are not interchangeable without changing how the plant talks to it.

Capacity is the same across the range

Every modular SLC processor supports a maximum of 3 chassis and 30 slots of I/O, up to 4096 inputs and 4096 outputs, limited in practice by processor memory and chassis power. Only the memory differs.

Memory backup and the battery

The replacement battery is the 1747-BA. Backup options are EEPROM or Flash EPROM memory modules.

Always turn off power to the controller before removing the processor and inserting a memory module. Rockwell warns this guards against module damage and undesired processor faults. The modules are keyed against improper installation.

Memory module compatibility

Note the J1 jumper. On the 1747-L514 and L524 the J1 jumper sets M1 versus M2 memory module operation, and invalid settings exist. The 1747-L511 has no J1 jumper.

Firmware and series

The same catalogue number has shipped with multiple firmware generations, and the operating system, series and FRN combination matters when you configure the processor in RSLogix 500. OS502 Series C FRN10 or newer is the current production release for the L553.

Read the OS sticker on the side of the module. If you send us both the catalogue number and the OS sticker detail we can match a replacement properly.

Digital input modules

Digital output modules

Combination modules

Analog modules

Chassis and power supplies

Reading a 1746 I/O number

Unlike most Allen-Bradley numbers, the 1746 I/O range carries meaning in the letters.

The digits give the point count. Sinking and sourcing are not interchangeable. IB and IV look similar and wire differently.

Rockwell migration cross-reference

If you are moving to Compact 5000 I/O, Rockwell publishes direct equivalents and a 1492 conversion module that reuses your existing field wiring.

The 1492 conversion modules are the useful part. They let you keep the existing field wiring rather than re-terminating every wire, which is usually the biggest cost in an SLC migration.

The processor migration path

Rockwell's route off an exhausted 1747-L553 is a CompactLogix 5380, catalogue 5069-L320ER, or the process variant 5069-L350ER, running Studio 5000 Logix Designer v33 or later.

The 1746 I/O modules are not drop-in compatible. They must be replaced with 5069 modules in a 5069 rack. Treat that as a separate capital project and budget accordingly.

Four things worth knowing

Some modules have no removable terminal block

These are fixed terminal and cannot be swapped without disconnecting field wiring: 1746-IA4, 1746-IA8, 1746-IB8, 1746-IM4, 1746-IM8, 1746-IV8, 1746-OA8 and 1746-OB8.

If one of those fails, budget the wiring time as well as the module.

Some outputs already have surge suppression

Built into the 1746-IB6EI, the 1746-OBP8 series B and later, the 1746-OB16E series B and later, the 1746-OBP16 and the 1746-OVP16.

On those, a suppressor at the load is not needed unless another contact is wired in series. On every other output module driving an inductive load, fit one.

The 1746 power supplies cannot feed the analog output modules

This one catches people. The 1746-NO4I and 1746-NO4V have connections for a user-supplied 24 V DC supply, and that supply must hold 24 V within plus or minus 10 percent.

Rockwell states plainly that the 1746-P1, P2, P5 and P6 power supplies do not meet that specification. You need a separate 24 V supply, not the rack supply.

Interconnect cables are ordered by length code

1492 cables come in 0.5, 1.0, 2.5 and 5.0 m and the length goes into the catalogue number: 005, 010, 025, 050. So 1492-CABLE005N is a 0.5 m cable.

Cable type depends on the module. RTBB for the 32 point modules, RTBO for the 16 point DC modules, RTBR for the relay modules 1746-OW16 and 1746-OX8.

What usually fails

Output modules before input modules. Relay contacts wear on operation count, and triac outputs fail on inductive loads without suppression.

Power supplies. Electrolytic capacitors dry out. A rack that resets intermittently or will not start on a cold morning is often the supply rather than the processor.

The processor battery. SLC 500 processors keep the program in RAM on a lithium battery. Flat battery, program gone. If you have SLC racks in service and nobody knows when the batteries were last changed, act on that while the plant is running. The part is the 1747-BA.

Do you have a current backup of the program? For a lot of SLC sites the honest answer is no, and that turns a module failure into a much bigger problem.

Migration, and why you might not want to yet

Rockwell points SLC 500 users at CompactLogix and Compact 5000 I/O. It is a real project: new hardware, RSLogix 500 programs converted to Studio 5000, and an outage.

If a module fails on a Tuesday, sourcing the original is faster and very much cheaper. Keep the SLC running with surplus spares while it suits you and migrate on your timetable rather than on a failure. We can supply the spares now and the CompactLogix hardware when you are ready.

Hold spares while they exist

Secondary market supply of a discontinued platform does not improve over time. It thins out and gets dearer as the installed base shrinks and the surplus gets consumed.

A spare processor, a spare supply and one of each I/O card you run is a modest amount of money against an unplanned outage.

We buy SLC 500

If you are migrating off SLC, do not scrap the old hardware. Processors, I/O, chassis and supplies are all worth money to the plants still running them. See Sell To Us.

Related

Allen-Bradley overview. CompactLogix for the migration path. PanelView if your terminal is on DH+ or Remote I/O.

Send us your catalogue numbers

One module or a full rack list. Include the series letter where you can, and for a processor include the OS sticker detail. Tell us what else is in the rack if you are adding rather than replacing. Quotes in NZD including GST.

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Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Rockwell Automation, Inc. Allen-Bradley, SLC, CompactLogix, RSLogix and Studio 5000 are trademarks of Rockwell Automation. All trademarks, brand names and catalogue numbers are the property of their respective owners and are used here for identification purposes only.