5370 L1 Controller Power Supply

Hey guys,

In the manual for the Compact 5370 Series it says that you must use two separate power supplies. One for the backplane power on the VDC+ and VDC- terminals and one for the FP+ and FP-. Do you have any experience wiring these? Does it REALLY matter? I know that since it is in the manual you should follow it but, is this overkill?

Thanks for your input.

I have never heard of that, what manual ??

I looked it up in the 1769-UM021 CompactLogix 5370 User Manual, Chapter 1, page 26.

The external Class2 or SELV-listed power supply that provides power to the CompactLogix 5370 L1 controller must be dedicated to providing
power to the controller only.

You should not connect the external 24V DC power source used with the CompactLogix 5370 L1 controller to any other terminals on the removable connector nor devices in the system, for example, the FP+ terminal or a bar code scanner, respectively.

Click to expand...

My guess is that this isn't a functional requirement, but rather a specification requirement. Because they specify NEC Class 2 or SELV power supplies, they're probably focusing on the current-limiting features of the power supplies, which are probably necessary for the controller to also meet Class 1 Div 2 hazardous atmosphere ratings.

It's always good to separate your analog signal power supply or your DeviceNet network power supply from the bulk power supply that runs things like controllers. And I always provide separate fusing and a control power relay between the main control power and the Output circuits.

The user manual goes on to specify:

The external 24V DC power source connected to the VDC+ and VDC terminals
on the removable connector must reside in the same enclosure as
the CompactLogix 5370 L1 controller.

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That's another one that I don't follow; my +24V DC supply has a 480VAC input and is located over in the separate panel that holds the AC subsystem, so that it's in a separate arc-flash hazard area.

I have a May 2012 edition of the 1769-UM021 and that drawing is on page 142 instead of page 144, and doesn't include the amusing fuse symbol, which must have been added in MS-Paint.

Some recommendations for separate power supplies have a basis in fact, like separation of analog loop or isolated network supplies.

When I use a 1769-L16 or -L18 controller next, I'm going to go ahead and get it a private, dedicated power supply of its very own.

Thanks Ken, I was thinking that it was possible for a small inductive load to induce a voltage on the backplane (output relay). However, I also would assume that the backplane power supply inside the PLC has another level of filtering and voltage regulators similar to the PB2 on the L32E.

And...is that sarcastic "I'm going to go ahead and get it a private.."? Sorry can't tell

bradal said:

...In the manual for the Compact 5370 Series it says that you must use two separate power supplies...Does it REALLY matter?...is this overkill?...

Click to expand...

Why the need for two separate power supplies?...

475553 - CompactLogix 5370 L1 Power Connector
Access Level: Everyone

bradal,

Basically, the VDC+ and VDC- terminals only supply 24VDC to the embedded power supply, which powers the controller and its embedded I/O. It also provides 1A@5V to the POINTBus backplane, which only powers the modules. It does not provide a supply to the V and C terminals of either the embedded I/O, or the POINTBus modules.

The FP+ and FP- terminals are linked to these V and C terminals and provide the necessary field power. So it should be suitably rated to power all field I/O devices.

If you choose to connect a single supply to both sets of terminals, you may induce noise from the field back into the controller's internal system power lines. This could potentially play havoc with the POINTBus modules on the backplane. The fact the embedded power supply is non-isolated makes it susceptible to noise.

Ken Roach said:

The external 24V DC power source connected to the VDC+ and VDC terminals on the removable connector must reside in the same enclosure as the CompactLogix 5370 L1 controller.

Click to expand...

Click to expand...

Ken,

Again, this is to help eliminate noise on the wiring from the power supply to the controller by keeping the power supply and its wiring as short as possible a distance from the controller.

It's your call at the end of the day guys, but bear the noise issue in mind if you ever run into weird goings-on while using only one supply.

Some more info...

475558 - Calculating System Power Consumption on the CompactLogix 5370 L1 Controllers
Access Level: Everyone

493329 - Master Control Relay (MCR) wiring for CompactLogix 5370 L1 controllers
Access Level: Everyone

493835 - Embedded Input or Outputs not working on the 1769-L1ER?
Access Level: TechConnect

471241 - CompactLogix 5370 L1 Controller will not power up; stuck in a power up sequence
Access Level: TechConnect

George