1771-PA Capacity

CaspianSage

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Does anyone know the current capacity of the Allen Bradley 1771-PA power supply?


Nothing on Rockwell's literature site. Have not been able to find it on the web...


Thank you!
 
Good find !

Remember that the 1771-PA was for PLC-2 systems and is pretty ancient. It will power a 1771 chassis with a 1771-ASB adapter, but not one with a PLC-5 controller.
 
Interesting Ken... I have been using it to power a PLC5/20 for about a year... and a P1 as well as a P2.

"The 1771-PA can power one 1771 chassis when used with any adapter, PLC-5 family processor.... "
From https://www.dosupply.com/automation/.../plc-5/1771-PA

So what gives ?





Good find !

Remember that the 1771-PA was for PLC-2 systems and is pretty ancient. It will power a 1771 chassis with a 1771-ASB adapter, but not one with a PLC-5 controller.
 
OK, I might be wrong about the 1771-PA specifically, or it might be working by coincidence, especially with a Series A 1771 chassis.

There's a big Knowledgebase article that we followed when putting together PLC-2 retrofits and conversions (KB 16474, TechConnect Required) and it calls out the 1771-P1, P2, and PA, as well as the 1777-P2 and -P4, as being inappropriate for use with the PLC-5.

In general, PLC-2 power supplies with Series A 1771 chassis (1771-A2, etc)were fine for PLC-2 controllers or I/O, while PLC-5 power supplies and Series B 1771 chassis (1771-A2B, etc) could be used together.

I recall running into a few instances like what you describe: "the knowledgebase says not to use them, but they work". I don't have the details about rise time, ripple, hold-up, or fault mode behavior, so I can't adjudicate which one is right.

When dealing with power supplies from the early 1980's, you can seldom justify spending a lot of research and testing time. The capacitors on the PLC-2 era hardware aren't getting any younger, while the installed base of newer hardware and its availability is high enough to make your guideline "scrap anything older than the Reagan administration".
 
Yet surprisingly I have better luck with our 1771-PA power supplies and Series A chassis, and associated 1771 cards than I do with newer 1794 FLEX and 1746 SLC platforms.

Not that I would ever recommend building a new machine with these technologies, and their obsolescence is a serious concern, we still have original 30 year PLC-2 input racks that just keep working (with the controller over time upgraded to PLC5, then PLC5-NP, in a new series chassis with new power supply). Fingers crossed in the next 5 years they'll be replaced with a new Logix platform and new IO.
 

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