How to select AB 1746-n power supply

[ceilingwalker]

hello again. I have been having problems with my control shutting down because of an RTD module fault. When I remove the load from the module it works fine. I have added four additional RTD probe's and I think it has put the power supply over the edge. The power supply I have is a 1746-P4 and it is installed in a 13-slot rack that is fully populated. When I go to I/O configuration and select "power supply" it brings up a message that says something to the effect that the power supply is overloaded. When I remove the four additional RTD's the problem goes away. That being said, how do I select the next larger power supply? Is it safe to assume that the next number higher (P5) supply would suffice? Thank you for the help.

 

[Ken Roach]

Actually, the 1746-P4 is the largest capacity power supply for the SLC-500; it can supply 10 A at 5V and about 2.88 A at 24V DC.

You might just have a configuration that can't be done in a single chassis.

The RSLogix 500 I/O configurator power supply check is a good tool, and there is a nice example of adding up the 5V and 24V loads of various I/O combinations in the 1747-UM011 User Manual and similar summary information in the 1747-SG001 Selection Guide.

It might make sense to split this application up between a 10-slot rack and a separate 4-slot rack for the RTD modules.

Are you using any Analog Output modules (1746-NO4V, -NO4I, -NO8V, -NO8I) ? Most of these have an option to be powered by an external source instead of by the backplane's 24V supply, which might put you back under the 24V limit.

 

[Ron Beaufort]

adding to what Ken has posted - there is a "secret handshake" involved with that "power supply calculator" you're using ...

http://www.plctalk.net/qanda/showthread.php?p=374646&postcount=18

 

[ceilingwalker]

When I run only the original four RTD's, no problems. When I run all eight RTD's, the system shuts-down and tells me that the module in slot 11 is generating a generic fault. I then have to shut down the system and restart it. After all 4 channels on the module are checked, I hear something pull-in and then I get a fault on the PLC and it's the slot 11 fault mentioned above.

 

[Lancie1]

Seems like your P4 power supply is overloaded. See Ken Roach's solutions in Post #3.