PLCs that can take 250VDC I/O

Hello everyone,
Are there any PLCs out there that can take 250VDC I/O directly without any opto / relay isolation with 24VDC conversion.
Thanks in advance,
Amit.

Power plant work, huh? I have used AB Flex I/O modules for 125vdc station battery type stuff, and AB also has a standard 125 VDC input module and an SOE 125 vdc input module. Try Siemens; TVA used their stuff to automate all of their Hydro plants. Some of the older ones had 250 vdc station battery voltage.

Spectrum controls has specialty I/O cards for the PLC-5 and SLC-500 series that meet your requirements. Here's the links to the card info sheets.

http://www.spectrumcontrols.com/pdfs/abio/1771sc-IMI16 0100026-02C DS_S.pdf
http://www.spectrumcontrols.com/pdfs/abio/1746sc-IM8I 0100039-02_D screen.pdf

Had this issue once when using Fluke data logger. Voltage was above accceptible input value. Used a voltage divider to get it below 10 V. Worked like a charm
CAUTION it was not grounded -- I think -
so even though the "signal is only 10V (or whatever) it is still at a 250 VDC potential above ground (in your case) if your DC is grounded.
(it has been many years since I had to do this so memory is a little gray)

Dan Bentler

My company performed the TVA automation as well as other hydro power systems. This is a common problem and you will find that AB, Siemens & Modicon can take 125 VDC not 250.

These systems are sometimes grounded in the middle of their potential, i.e. voltage divider, to create +125 and -125 VDC as referenced to ground or 250 VDC as referenced end to end.

If you are stuck with 250, I believe you will find it difficult to find I/O cards to handle it. I was not aware of the Spectrum equipment, so I can't comment either way, but I will definitely stick it in my memory bank for further evaluation in the future. Thanks for the tip Ken!

Good Luck and feel free to ask questions, I will help where I can.

Thanks for the info, fellows.
MGVOL is correct, it is a power plant application. We have a programmable relay that takes care of the critical functions, but I am falling short of I/Os. Thats the reason I am on the lookout for a PLC which can talk to my relay using Modbus and directly interface with the switchgear controls. Alternate ofcourse is to use 24VDC interface i/o but it will mean more hardware, complexity and reliability issues. Thats what the local Siemens people are suggesting anyways.
Does AB PLCs support Modbus ? Do I need a Modbus server to enable a PLC and my relay to talk to each other ?

Thanks, Amit.

Thanks MGvol, Ken, leitmotif and hydropowerguy for your inputs.. I appreciate your feedback. I am looking over the spectrum controls products suggested by Ken. I hope I get support for them in India. Amit.

Aartech said:

Does AB PLCs support Modbus ? Do I need a Modbus server to enable a PLC and my relay to talk to each other ?

Thanks, Amit.

Click to expand...

Go over to http://www.prosoft-technology.com

In particular they do 3 modbus modules

http://www.prosoft-technology.com/content/view/full/135

http://www.prosoft-technology.com/content/view/full/658

http://www.prosoft-technology.com/content/view/full/659

I have heard reports that they are good but have never used one myself.

Hello aartech;

Siemens does offer 16 point 250 VDC input modules (actually 230 VUC, both AC and DC) on their S7-400 platforms (6ES7 421-1FH00-0AA0 and 6ES7 421-1FH20-0AA0). And the S7-400 can be a master or slave on Modbus, with the serial CP441-2 and Modbus loadable drivers (expensive package, but it works well).
Hope this helps,
Daniel Chartier