UPS and Transformer Selection for PLC Control Panel

[YogeshG]

Dear All,

I have Siemens PLC with IO modules. I want select proper 24 VDC power supply ,UPS and Transformer. Following are the Siemens PLC and Modules.
1. CPU 315-2 PN/DP [6ES7 315-2EH14-0AB0] –1 nos.
2. Digital input module DI32 [6ES7 321-1BL00-0AA0] -25 nos.
3. Digital output module DO32 [6ES7 322-1BL00-0AA0] -25 nos.
4. Analog input module AI 8 [6ES7 331-1KF02-0AB0] -4 nos.
5. Interface Module IM 153- 2 [6ES7 153-2BA02-0XB0]- 2 nos.
6. 8 channel Relay Board -25 no.
7. power supply PSU100D 24V/6.2A (6EP13331LD00)--2 nos.

Before selecting UPS and Transformer what factors I need to consider. Transformer is Step down 440 V to 230 V AC. For UPS and Transformer calculation I need to take Power Supply input Current. Input current is 2A for each power supply so total current will be 4A.

VA=230*4
VA=920
KVA=0.92

UPS and Transformer rating will be 1KVA.

Please let me know whether my above calculation is right or wrong?

Regards,
Yogesh

 

[petersonra]

that seems like a lot of VA for two small power supplies, but if that is what the spec sheets say, that would appear to be the right number.

It does not appear like you have accounted for the power that feeds all the I/O modules, just the two power supplies.

Given the number of I/O modules I am skeptical that the number of power supplies is adequate. 25 relay cards can eat up a lot of power.

 

[gar]

150625-0855 EDT

I would be inclined to directly connect a 12 V car battery to the PLC power input, and charge the battery and power the PLC with a voltage regulated power supply with vertical overload current limiting (not foldback).

Possibly set the power supply voltage slightly over 13 V to trickle charge the battery. Current limiting would be set somewhat above peak current required for the PLC.

.

 

[Tony S]

Personally for a panel that will (almost guaranteed) find other things added I’d err on the side of caution and install a larger Tx.

1KVA would be cutting it too fine for me.

PS. ^^^I don’t know where the car battery came from^^^

 

[gar]

160627-0906 EDT

Tony S:

Why did I suggest a car battery?

The original post indicated a UPS. Instead of using a UPS I was suggesting a battery at the input of the PLC and using a regulated power supply as both the battery charger and the normal power supply to the PLC. Time duration of backup is easily set by the size of the battery selected.

I did make a mistake. Two 12 V batteries are needed to provide 24 V, and thus the constant charging voltage would be about 26 V.

.

 

[petersonra]

160627-0906 EDT

Tony S:

Why did I suggest a car battery?

The original post indicated a UPS. Instead of using a UPS I was suggesting a battery at the input of the PLC and using a regulated power supply as both the battery charger and the normal power supply to the PLC. Time duration of backup is easily set by the size of the battery selected.

I did make a mistake. Two 12 V batteries are needed to provide 24 V, and thus the constant charging voltage would be about 26 V.

.

sola makes a nice little 24vdc UPS. why make your own?

 

[gar]

150627-1022 EDT

petersonra:

You have a good suggestion.

One link to Sola is:
http://www.solahevidutysales.com/pdf/ups/SDU-DC-DIN-Rail-UPS.pdf

.

 

[Tony S]

Something that is puzzling me (other than car batteries), why the need for a UPS at all. If power is lost to the PLC, whatever is being controlled should loose power. It would be bad design if it didn’t.

Every PLC I’ve worked on had battery backed memory. In configuring the unit you specified retain last I/O state or reset on power loss.

I’ve only used reset on power loss a couple of times. It would be catastrophic on most of our machinery.
The times I have use it was on induction furnaces, I needed it to do the full system safety checks before power was restored.

 

[iwire]

Something that is puzzling me (other than car batteries), why the need for a UPS at all. If power is lost to the PLC, whatever is being controlled should loose power. It would be bad design if it didn’t.

We have no idea what the OPs PLC is being used for.

In my work we often have a the PLCs on dedicated generator backed up circuits with small UPS units at the controllers even though the equipment they control is not on generator or UPS power.

In my situation the 'machine ' the PLC controls is spread all over the building with dozens of different supplies. The PLCs need to stay up and running to monitor and log conditions regardless of the power being on or of to different parts of the equipment.