Do DC input PLC's work with AC?

[86turbodsl]

I have done exactly what you are trying to do with an AD PLC. It's a really easy solution. Place a 2.7k 1/4w resistor in series with each input - no caps needed. That will limit current to a safe value, since the peak voltage of a 24vac RMS signal is around 34v. That takes care of the hardware. In DirectSoft, use the "Off-Delay" I-box to filter the inputs, since they are actually turning on and off 120 times a second.

--X0-----------------------------OFF-DELAY IBOX, K30---C0 output

--CO-----------------------------Your program here.

Use the C-bit output of each Off-Delay timer to control your program. Note - each input will need its own timer. Works like a charm, and very simple. Just make sure to document this well in DirectSoft with comments.

Hope this helps.

rpoet

The 24V supply on the plc will work for the tstats. So I shouldn't need this, but thanks for the info.

 

[keithkyll]

The plus side of the 4.7 cap goes to the output of the diode. The minus side goes to ground. Doesn't matter now, the 24DC idea is a much better solution.
MOV's won't supress arcs very well. You need a Snubber. .05 in series with 50 ohm, or .1uf/100 ohm. They make them in a single unit. look up Snubbers. It's debateable whether you need them or not. Your contactors are fairly small.

 

[eebads2391]

Have a look at the lower part of this page

http://www.eod.gvsu.edu/~jackh/books/plcs/chapters/plc_wiring.pdf

Mike

 

[86turbodsl]

What am I looking for?

 

[Lancie1]

Turbo,

I have interfaced Automation Direct PLCs to HVAC systems. For HVAC systems with 24 VAC controls, I like to use one of the DL-105 units that have actual 24 VAC Inputs and Outputs. For example, the flollowing DL-105 PLCs all have 24VAC inputs: F1-130DA, F1-130DD, F1-130DR, F1-130DD-D, and the F1-130DR-D all have input terminals X4, X5, X6, X7, X10 and X11 as dual 24VAC/ 24VDC inputs.

The F1-130AA, F1-130AR, F1-130DA, F1-130DR, and the F1-130DR-D also have output voltage ranges that will accept 24 VAC.

Therefore, looking at the overlaps, F1-130DA, F1-130DR, and the F1-130DR-D all have six 24 VAC inputs and 24 VAC outputs. The ones with an "R" have relay outputs with voltage range of 12 to 250 volts AC and 12 to 30 VDC.

You may want to consider swapping the DL-06 for one of the DL-105s, if one has enough I/O for your job. Heck, at $159 each, use two of them! That would give you twelve 24VAC Inputs and 16 24VAC outpus! You will need 120 VAC for powering the PLC itself.

Before someone jumps on and says the inputs are only rated for 24 VDC, be sure to check the Specifications, not the brochures, before you tell me this won't work!

F1-130DR - Wiring diagram and specifications

Power Requirements

Voltage range . . . . . . . . . . . . . . . . . . . . . . . . . . .94-240 VAC (30 VA), 100-240 VDC (30 W)​


DC input specifications 

  

Number of input points . . . . . . . . . . . . . . . . . . . . . . .10 (sink/source)

Number of commons . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 (isolated)

Input voltage range . . . . . . . . . . . . . . . . . . . . .(X0–X3): 10-26.4 VDC,(X4-X11):10-26.4 VDC or 21.6–26.4 VAC

Input impedance . . . . . . . . . . . . . . . . . . . . . . .2.8 K@ 12-24 VDC​


ON current/voltage level . . . . . . . . . . . . . . . . . . . . .> 3 mA / > 9 VDC​
OFF current/voltage level . . . . . . . . . . . . . . . . . .< 0.5 mA / < 2 VDC​
OFF to ON response . . . . . . . . . . . . . . . . . . . . . . . . . . .X0-X3: 50 μs​
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .X4-X11: 2-8 ms​
ON to OFF response . . . . . . . . . . . . . . . . . . . . . . . . . . .X0-X3: 50 μs​
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .X4-X11: 2-8 ms​
Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .None​
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Relay output specifications​
Number of output points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8​
Number of commons . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 (isolated)​


Output circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Relay​
Output voltage range . . . . . . . . . . . . . . . . . . . . . . . . . . . .12-250 VAC, or 12-30 VDC​
Maximum voltage . . . . . . . . . . . . . . . . . . . . . . . .265 VAC, 150 VDC​
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[parky]

There is a major problem n using ac on dc input.
1. even if rectified the chopped waveform will turn on/off the inputs at a rate of 50 hz (100 if brige rectifier).
24v ac rectified & smoothed will give 1.414 X the ac value & if not smoothed well enough could trigger the input off a 50 hz.
Had this once on a system where the DC supply had a duff capacitor.
a sensor on the input when on was flicking at 50 hz so the delay timer was resetting only found it by measuring the powere supply it read 20 volts but the ripple on it was dropping it below the threshold of the input.

 

[86turbodsl]

I got it working correctly. The DC, I used the onboard supply. I have 50% more current off that supply than I needed. It works great. I needed the DL06 because it has 20 inputs and 16 outputs. And I still have 3 modules in it. Two RTD modules for temps and an extra module for relays.