24VAC Inputs for Automation Direct DL-205

General
1

I have a project for my furnace at home I want to do, which like all furnaces is 24VAC controlled.

I have a nice collection of DL-205 racks, CPU’s & IO, but the inputs are 24VDC. The A-D website shows only 120 or 240 AC inputs for these.

Without buying a bank of interposing slim relays ($55.00) has anyone ever tried to put 24VAC into one of these DC inputs using a diode?

I have before tried the diode to a 24VDC miniature relay, but the coil chattered from the half wave DC and I had to break down & buy AC relays.

2

Before I tried to half wave rectify AC to a PLC DC input point, I would spend some money on a Click or Click Plus which has software that is free and far superior to DirectSoft and has support for AC inputs that cover that voltage range. I think you’d have to use relay outputs. The only PLC I have run across with triac outputs for 24VAC was a Schneider Zelio (yuck).

https://www.automationdirect.com/adc/shopping/catalog/programmable_controllers/click_plus_plcs_(stackable_micro_modular)/stackable_i-z-o_modules/c0-08ne3

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3

I have a shelf full of DL205 stuff, they are relay outputs, even though all the outputs will be DC and powering relays.

I do have the Click software and have done Click projects, but no Click’s or IO on hand.

I also have plenty of SLC parts on hand, but I want a smaller footprint of the 205.

I’m just trying to do this with what I have for minimal cost.

4

diode feeding an RC circuit might work, depending on the required response time …

5

Being a furnace, a response time of 50 msec’s would be fine, so that’s not an issue.

I’m thinking about putting a test program in and feeding one input constant 24VAC through a diode and a second input the power through a repeating timer and let it run

EDIT: And through the repeating timer also send pure 24VDC pulsing to a third input and flag any time lag or failures of the AC through a diode input.

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6

Actually, digging into my Useless PLC Crap pile I have a ML1500 with a few IO cards (including a DeviceNET module I won’t ever use) and a ML1100 but no IO cards and it doesn’t have enough inputs.

If I had another 17xx-NET-ENI (Mark can fill in the number better than I can remember it) the 1500 would be better as I could have my home automation PLC message it.

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7

A TOF (essentially a debounce) could be a proxy for an RC circuit with the simple diode approach, no?

8

Yes, it should work.

But, after finding the ML1500 I mentioned earlier, I’m leaning toward using it. Especially after deciding that the SLC5/03 running my Christmas tree doesn’t need the WiFi repeater or NET-ENI it has, and I could use that one for the furnace and then have a standby repeater. (The main network switch in the basement is about a 8 foot run from the furnace, so I’ll run a CAT5/6/7/[whatever number is out then] cable)

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