Wiring a Panel with an FX1N-14MR-ES/UL

[Matt S 0]

OK. Simple question, but I don't do much of the wiring for the PLCs I program (actually I don't program too much either). I have four 24VDC outputs (solenoid valves - 190mA current draw each) that I need to power via an external 24VDC power supply. Electrically, how do I get power to the Y000-Y003 output terminals of the PLC. And how do I figure in the COM0-COM3 terminals for the common signal? The end user I'm working with doesn't have any electrical drawings, and it's been a few years since I've had to wire a panel, and it took a bit of work to convince him to get an external power supply after the PLCs +24VDC service supply would cut out after taking more than a 400mA load... He also has a selector switch for each output that he's wired serially on the output side. He wants to use them to keep outputs from turning on. Sounds odd, as I would have taken the +24V signal on one end of the selector and the signal to an input on the PLC. Any help would be greatly appreciated.

[Crossbow 295]

Well first thing is which side of the power do you want to switch? Since it's a relay output, you've got your choice. Each COM terminal is tied to certain outputs (which are detailed in the FX1N Hardware Manual available at www.meau.com). If you put +24 into the COM, that is what you will get out the outputs. Then you wire the PLC outputs to the solenoids, and hard wire the negative side of the 24VDC power supply to the solenoids. There are wiring diagrams in the hardware manual. You absolutely CANNOT use the PLC's internal 24VDC for loads over 400ma. It's designed to be run through switches into the PLC's inputs, not to power heavy external loads.

[Paul Ked 0]

Monkey and machine gun immediately spring to mind here, I'm pleased to know you are only working at 24V

[Matt S 0]

Luckily I'm not the one working inside. Crossbow, after looking at the H/W manual (the user had thrown his out) last night, I see exactly what you're talking about. Additionally, he told me the current draw for the solenoids was 19mA each. I looked at the sheet and when I saw 24VDC .19A I told him that it was drawing 190mA each, not 19. Math iz gud... Now to convince him to switch the selectors to inputs rather than breaking the +24VDC input signal to the COM0-COM3 terminals on the PLC. Edited 12 Oct 2007 by Matt S

[Crossbow 295]

Breaking the power to the output commons is actually common practice in many PLC based control panels. Many times, the ESTOP switch will remove the power from the PLC outputs, which in effect stops them all from working.