DL205 and DL05 Question

[apatsfan]

Good morning all. I recently wrote a small program and loaded it into  the DL205 with the DL230 CPU and D2-08NA-1 as my input and D2-08TR for output. I'm using four 120v Reed switches as the control for my pump starter. I wired it up and it works great.

I go into the field and install a D0-05AA (brick) into the existing system, I then wire up the same 120V Reed switches used earlier. I then turn the system on and find out all my Reed switches have failed. How could this happen?

[b_carlton]

Do the input LEDs on the DL05 light when the reed switches are made? If not then you have a wiring error. Post your wiring schematic for the DL05 and we'll take a look.

[rlp122]

It is the inrush for the AC inputs.  Inrush is about 10A so reed switches just don't hold up.  Sorry to be the bearer of bad news.

[Controls Guy]

Seriously?  10A inrush?  Wow.  Even so, should be able to cure that with a current limiting resistor in series or switch to DC inputs.

[b_carlton]

He didn't say the reed switches were part of the output circuitry. But he wasn't exactly clear either. I imagined them as inputs to the PLC.

[Controls Guy]

@rlp122 seemed to be thinking the same as you are, and further claiming that the 120V inputs have a 10A inrush, which seems extremely high.  Maybe I misread his post.

[apatsfan]

Sorry for taking so long to reply.
@b_carlton I do not have a drawing for this "supposed to be simple" job. I will try to draw one up. As soon as I put power to the unit all four led inputs were lit. I new there was trouble!

@rlp122, @controls_guy. When I did the testing on my workbench I was using DL230 CPU and D2-08NA-1 for my inputs. This worked without flaw. But in the field using the 05 the reed switches failed.
Is it the Inputs for the two PLC's have different inrush capabilities?

Thanks for the help! I'm new to the Direct Logic family and really appreciate the help.

[rlp122]

You didn't mis-read it.  It's been a long time since I tested the 120VAC inputs so 10A may be high, but that is what I remember for the inrush. What I do remember is that it was way more than any reed switch could handle reliably.

The input circuitry on all of the Koyo AC inputs is similar.  If you look at the simplified drawings in the user manual you will see a capacitor that sits across the opto-isolator that has to charge when the input closes.  It is the capacitor charging that causes the inrush.  To break it down simply, the RC constant is too small to level out the spike.

Regardless of my potentially faulty memory, I have never had good luck with reed switches on AC inputs.  They tend to weld in anywhere between 1 to 100 cycles.

[Controls Guy]

Wow - that's amazing. 10A into an opto circuit.  I'd never have guessed.  Maybe use the reed switches to drive interposing relays if he can't switch to DC inputs.  Come to think of it, how's the inrush on the DC?

[rlp122]

DC is nothing to speak of inrush wise.  DC inputs handle reed switches just fine.