Wiring a simple 24v DC light on an output terminal on a PLC

Question

I am using a Micrologix 1100, part number 1763-L16BWA. I have been able to get the input side working, but can’t seem to figure out the wiring for the output side. I also have an 1762-IQ8OW6 extension.

I have some simple lights that “light up” when I connect them to the DC+ and DC- terminals so I know the lights work.

I have created a simple ladder program that has one rung for each output on the PLC and each output on the 1762-IQ8OW6 extension. Each rung has a separate bit that turns on or off that output:

All the outputs on the PLC and the extension are activated:

However, no matter how I have tried to wire it, I can’t get the light to turn on using the output terminals. I have connected the VAC/VDC terminal in the output to DC+ and then connected one end of the light to the other output terminal and the other end of the light to DC-. I have also tried the reverse.

I have tried wiring all 12 of the output terminals.

I have watched lots of videos, but they are all doing more complex things. It seems like everyone knows how to do this but me. How do I wire a 24v DC light to an output terminal on the PLC?

Please help.

Thanks.

[EDIT]

AC Input connect to 110V.

D+ and DC- power from PLC. DC- is connected to one end of the light. Second end of the light is free so I can connect to various terminals. Two wires out of DC+ - both connect to the 1762-IQ8OW6 extension VAC/VDC terminals.

There are two VAC/VDC terminals on the 1762-IQ8OW6 extension. Each has 3 separate output terminals (0, 2 and 4) and (1, 3 and 5).

Touching the free end of the light to either VAC/VDC terminal in the 1762-IQ8OW6 extension illuminates the light.

Wiring Diagram.

Could you supply a diagram of how you've tried to connect things? — Unimportant, Nov 11 '20 at 17:24
You have nothing wired to the outputs on the base unit. The photo doesn't reveal the wiring on the output module. Are the extension module output indicator LEDs on? Tip: when you're doing the screen grab shrink the window width to eliminate all the white space in the centre and then crop the irrelevant parts out. — Transistor, Nov 11 '20 at 17:49
@Unimportant - I have attached a wiring diagram. Hopefully it is sufficient. — Garet Jax, Nov 11 '20 at 18:31
Your approach and wiring seems correct. The manual says that those two DC/AC terminals are connected internally so you don't need to run two wires over. Can you hear the relays click when you go from standby to run? — Transistor, Nov 11 '20 at 18:43
Disconnect the 24VDC wires from the output card, then check the outputs with your ohmmeter. Do you have continuity between the common terminal (VAC/VDC) and the output terminal (OUT 0)? If not, try turning off the output and check again. — Ben Miller - Remember Monica, Nov 11 '20 at 19:19
@Transistor - I don't hear any clicking when switching modes between program and run or when enabling or disabling an output. — Garet Jax, Nov 11 '20 at 19:59
@Ben Miller - I tested a few of the 12 output terminals. I connected one end to VAC/VDC and the other end to the corresponding terminal and there was no continuity on any of them. — Garet Jax, Nov 11 '20 at 22:09
@GaretJax In that case, it doesn't matter how you wire them, they won't work. Have you tested the embedded outputs that are on the main controller module, not the expansion card? — Ben Miller - Remember Monica, Nov 11 '20 at 22:11
@Ben Miller - Yes I tested all of them. Am I doing something wrong in the PLC - it just seems unlikely that all Output terminals are broken. — Garet Jax, Nov 11 '20 at 22:15
@GaretJax Agreed, it is unlikely that they will all be broken. Work on getting the embedded I/O to work first. If you've got O:0/0 turned on (which you do in your screenshot) and you see the indicator for O/0 on on the display (which it appears to be in your photo), then you should be reading close to 0 ohms between the VAC/VDC and O/0 pair of terminals, located just to the right of your AC power input cable. Also, check the cross reference for B3:0/0 and O:0/0 to make sure you aren't turning them off somewhere else. — Ben Miller - Remember Monica, Nov 11 '20 at 22:32
@GaretJax Something else: Touching the loose screw on terminals doesn't always produce a reliable connection. Stick some wires into the terminals, and touch your meter leads to those wires. — Ben Miller - Remember Monica, Nov 11 '20 at 22:35

score 1 · Answer 1 · answered Nov 23 '20 at 01:26

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The given micrologix seems to have relay outputs, rather than sourcing outputs: This means that in order to power your sink devices, you need to supply voltage separately to the VAC VDC Pins. Connect the DC OUT + from the input terminal block to VAC VDC in the 15th pin of the output block. Next, connect one terminal of the LED to the O/5 terminal and the other terminal to the DC COM on the 8th pin of the input terminal block, because they share the same common according to the terminal diagram of the L16BWA, The shading in the following terminal block illustrations indicates which terminals are tied to which commons.This should make the output energizable through the PLC.

Please consider marking this as the answer if it helps!

answered Nov 23 '20 at 01:26

BikerDude

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Thanks - I got my hopes up. Unfortunately this didn't help. I'm thinking more and more that the Micrologix 1100 has been damaged. – Garet Jax Nov 23 '20 at 23:46
Were you able to check the resistance between VAC and O/5 when you have it switched on? Just asking as the relay might be an opto type, and might not click. – BikerDude Nov 24 '20 at 12:44
@GaretJax can you try this: https://i.ytimg.com/vi/R26PZ7Cynlg/maxresdefault.jpg It utilizes an external power supply, the V+ Goes into the VAC VDC and the LED goes to V- and O/5. With our earlier experiment it might have been a grounding issue. Still would recommend using a DMM and checking voltages and resistances(When deenergized) across relays. – BikerDude Nov 24 '20 at 13:16

vir · Answer 2 · 2020-11-11T17:39:11.840

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Looks like you need to wire 24V into the "VAC/VDC" terminal next to the output you want to control the light, wire the positive terminal of the light into the output terminal itself, and wire the negative terminal of the light to ground (COM or power ground, not earth ground).

Edit: the manual states that the 24V out can only supply 250mA. Does your lamp draw more than this?

edited Nov 11 '20 at 17:39

answered Nov 11 '20 at 17:13

vir

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According to the explanation given in the question, that's what was done. – Unimportant Nov 11 '20 at 17:25
These lights take < 20mA. They don't appear to have polarity. One end is labelled X1, the other X2. – Garet Jax Nov 11 '20 at 18:26

score 0 · Answer 3 · answered Nov 11 '20 at 22:29

Since you don't hear any relay clicking to match the output LEDs it seems as though the relays are not picking up. The relays may be powered by a separate voltage source than the logic which is likely to be 5 V. It's possible that part of the PSU has failed although I'd expect the PLC to indicate a fault in that case.

Check the diagnostics page on the RS Logix software.

Wiring a simple 24v DC light on an output terminal on a PLC

3 Answers3