Reply To: Controllogix – Controller sizing/IO cards/Power questions

Soolocks5779George Barnette
Karma: 166
Rank: Jedi

Antuaneth hi, and welcome to the forum. As Sean said, 120 V control creates some problems. I worked for years in the seafood industry in Alaska as an industrial electrician/PLC programmer. I had to work on a lot of European equipment that used 230 VAC control power, and they were very dangerous and parts were hard to get.

In my job now, my company almost exclusively uses 24 VDC. Easy to work with and safe to troubleshoot. If you do need 120 for say hydraulic solenoids or other high current devices, you may want to check the current rating on the output cards (modules) and possibly use interposing relays for the outputs. I’ve also had to install surge suppressors on the 24 VDC relays to keep them from having current spike issues when de-energizing. I had a lot of trouble with that on some totalizers one time.

Lastly, unless the customer requests otherwise, we supply sink/source modules for everything, mainly because it is easier to configure the wiring for a device that’s changed from say PNP to NPN than it is to change a module if a device cannot be found or is hard to get. And, I’m not into hardware design much; I did some as a favor a couple years back and although I learned a lot, it’s not for me. Good luck and if this was any help at all, then you made progress!!