# of Expansion Modules on M/L 1500

How many 1769 I/O modules can I add directly onto a 1764-LRP Micrologix processor with no auxiliary power supply?

I have to expand a small system. Right now it has 3 1769 modules already attached to the base and I need to add a total of 5 more.

Space is an issue and I'd like to add as many modules as possible directly onto the M/L before using the expansion cable and power supply.

Thanks

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1764-um001_-en-p.pdf

Series B or higher will support 8 modules and Series C or higher will support 16 modules. Page 1-7 and 1-8.

1769 modules have a "distance rating" that determines how far they can be from a power supply. The most common distance rating is 8, but you need to check the 1769-TD006 publication (Compact I/O Technical Data) for your specific modules.

For that reason, the maximum number of I/O modules that can be connected to a 1764 controller base is 8 modules.

The 5V and 24V DC usage of the system are the other limiting factor. The 1764 controller base provides 2250 mA at 5 VDC and 400 mA at 24VDC.

There are several ways to calculate the power usage for a MicroLogix 1500 expansion I/O system.

You can do it on paper with the information in the 1764-UM001 User Manual for the MicroLogix 1500, in Appendix F.

There's an Excel spreadsheet for system layout/sizing available from the AB.COM website.

Or you can punch all the data into Integrated Architecture Builder.

Let's say for the sake of estimation that you have a 1764-LRP with four 1769-IQ16 and four 1769-OB16 modules. These get all of their power at 5VDC and none at 24VDC.

1764-LRP consumes 380 mA at 5V DC
1764-IQ16 consumes 115 mA at 5V DC
1764-OB16 consumes 200 mA at 5V DC

Total = 380 + 460 + 800 = 1640 mA

So four IQ16's and four OB16's would bring you well under the 2250 mA limit for the MicroLogix 1500 base.

Run those calculations for your actual modules !

Thank you, Mark, for that information about Series C bases and the difference between the various hardware series and their capacity. I was looking strictly at the power consumption and the "distance factor".

The user manual does remind you that running 16 modules does require an expansion bank cable and an expansion power supply.

Thanks guys.
I read through the manual but It wasn't clear to me.
I'll read over out those resources you mentioned again