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SIMATIC S7-400 / S7-400H / S7-400F /FH

Power Consumption

Thread Starter: Sohail   Started: 5/16/2008 10:54 PM   Replies: 4

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  5/16/2008, 10:54 PM
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Dear All, how i calculate the power comsumption of each PLC input/out module installed in the rack?what r the factors need to take in consideration when going to select the PS for racks? Awaiting for response Thanks
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  5/19/2008, 5:49 PM
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Sohail wrote:
Dear All, how i calculate the power comsumption of each PLC input/out module installed in the rack?what r the factors need to take in consideration when going to select the PS for racks? Awaiting for response Thanks


Hi,
if you take a look at the ST70 catalog (www.siemens.com/simatic/printmaterial) you can see that for each module has a current consumption from load voltage L+ (for external PS consumption calculation) and a current consumption from backplane bus DC 5 V

 (for S7-400 PS consumption calculation).


Denilson Pegaia
Siemens Mercosur / Brasil
Automation and Control Division
- Technical Support & Hotline -
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  5/20/2008, 7:22 AM
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Please mention, that all IO signals would consume power too (from 24V).
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  6/27/2008, 5:10 PM
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We can design in different ways, simplest way is, use rack PS for modules' back plane and for I/O from field use seperate PS.

To Calculate Rack PS add the power consumption of each module at 5v backplane, which is available in tecnical spec of every module.

To calculate Field I/O PS, add the wattage of all the field equipmets.

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  7/1/2008, 6:15 PM
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Power budgets can be a fun one to calculate (yeah, right).
I presume you are doing this for proper sizing of your DC power supply in the cabinet.

There's the power for the profibus interface module.  If it's a ET200M type, as you add modules, they consume more power. 
Quiescent power + power consumed by each module\
Per Module: Quiescent Power + Power per point.  If you are using modules with diagnostic capabilities (digital in or digital out) they also consume power for the diagnostic function.

Know the power consumption of your devices.  We've been surprised by the consumption of different field devices, compared to the listed currents. 

Finally, recommend doing a power test where you measure the current consumption with the system active.  Based on my experience, your consumed power will be less than what you calcuated, but you don't want any surprises.

The worst situation I've seen is when a thermal/magnetic breaker was used for a DC supply output.  As the DC current approached the published max asymptotically, the breaker never tripped.  When the power supply ultimately failed, it took a lot of equipment out with it.
Thankfully it was not my design. cool
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