Bulk Power Supplies

[CHRISC1024]

I have a quick question on bulk power supplies. If I'm using (4) P&F isolated power conditioners, can I use a standard 24VDC bulk power supply? Most installation I have seen don't have a Fieldbus certified bulk power supply. I've been under the impression that as long as it is an isolated power supply (no connection from the +24V or Common to ground) that if can be used to supply the 24VDC for the isolated power conditioners.

[Mike ONeill]

The whole point of the isolated power conditioners is to enable the use of any bulk DC supply less than 32V without the input side affecting the segment side. The FF certification tests essentially confirm that the isolation works properly.
Since the output of the power conditioners is isolated (some old P+F models are not), it doesn't matter if the bulk supply is grounded (it usually is).

[CHRISC1024]

Thanks Mike. That's how I understood it but I had a conversation last week and it was discussed that we needed to use a certified bulk power supply as well. The issue that currently exists is the older P&F conditioners are NOT isolated thus I believe the issue (if one existis) is in the pwoer conditioner.

We are planning on letting the existing power supplies power just the FFLD linking device and adding a second power supply to power the new isolated power conditioners. I don't think that having isolated condtioners AND the bulk supply powering both would cause an issue but better to be safe and wire it up totally isolated.

[tklatt]

Hello Chris,
as Mike already stated: there is no need for a certified bulk power supply! When using an isolated FF power conditioner you can power both parts of your application from the same bulk power supply. I don't see any problem.

[jhgross]

Chris,

We have found that one of the most important specs on the bulk power supplies (besides voltage and current) is rise time.
The bulk power supplies may supply the FF networks and the FFLD, should meet the requirement of 90% VDC in 10 ms.

See attachment.

James Gross - jhgross@ra.rockwell.com
Sr. Sys. Eng.
Process Automation Group
Rockwell Automation