Relay Timers

Snyd1

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Jun 2018
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Alright, sorry to bring this here but I have been banging my head against the wall over something that is probably a pretty simple circuit.

Sequence
1.)Press start
2.)pump runs for 15min (misc interlocks for flow)
3.)need to repeat every 45min to circulate
also need start to reset 45min timer and start immediately for 15min and continue cycle as if from 1 basically

Is this achievable with a setup of relay timers?

Our typical timers

700FSB3HU23
700FSA3HU23

Would be so much easier with a cheap PLC.
 
So Timer-Relay (TR) #1 is set for 15 minutes, and while energized the pump runs. When TR-1 times-out, an NC contact of TR-1 energizes TR-2, which is set for 45 minutes.

When TR-2 times out, a NC contact of TR-2 again energizes TR-1.

Rinse and repeat.

Am I missing something obvious?
 
Yes, it can be done with relays and timers.
I do not recommend it though.

By the time you do all the wiring diagrams, interlocks, materials, wiring and get it running, someone will add something else.

the panel wiring is a trade off.
the plc wiring and programming will allow for changes that can be done quickly rather than having to redesign the wiring and discover that you are out of room and need a new panel.

I would buy a micrologix 1400 with triac outputs or something similar.

james
 
I guess the restarting part is throwing me. Maybe I do not understand the timers well enough or maybe I am trying to use the wrong timers for the application. Wouldnt I need to hold TR-1 coil in, I couldn't just pulse it with the start button and run my cycles? Here is what I have

TIMERS.PNG
 
It could easily be done with timing relays but i would advise against it. An AB Micro810 cost less than $10 more than just 1 of those timing relays, so if you need more than one timer, the PLC is significantly cheaper. Also, using the PLC (really is more of a programmable relay than a PLC)makes wiring, troubleshooting easier, and future modifications simpler.
 
Yes I have worked with an Micro810 before and would love to use one for this, not sure I can convince them.

Wish I could say this is easy for me, real lack of experience with relay timers. I am leaning to a one-shot timer like the 700-HT3 in place of CR1, have the one-shot for 15min and have it be stroked by another timer set at 45min then use a second set of contacts on the start PB to reset the 45min timer if in progress. It seems silly though to put in a timer that cost almost as much as a PLC.

Had some labels messed up on my first drawing.

TIMERS2.PNG
 
if you are trying to justify costs, that's easy.

get the costs for the timers, relays, pbs
do the same for the plc
compare the wiring time for each.
compare the programming time versus the relay debug time.
then have the costs of a modification of a new function, that should convience them.

james
 
Schneider RE17RLMU.
Assymetrical flash timer, power it on and it "flashes" until you power it off. The on flash and the off flash are independently adjustable from 1 second to 100 hours, and it can be powered on 24-240V AC or DC.


There are certainly merits to using a small PLC instead of relay logic. But if you are really pushed for cost (or just want to keep it simple), a simple start-stop circuit with one of these will do the trick.
 
Schneider RE17RLMU.
Assymetrical flash timer, power it on and it "flashes" until you power it off. The on flash and the off flash are independently adjustable from 1 second to 100 hours, and it can be powered on 24-240V AC or DC.


There are certainly merits to using a small PLC instead of relay logic. But if you are really pushed for cost (or just want to keep it simple), a simple start-stop circuit with one of these will do the trick.


I like this, looks like the timers reset when power is lost. I guess I just need to find a way to break my latch when they want to start during the 45min time using the same start PB...like a flip flop resart.
 
I like this, looks like the timers reset when power is lost. I guess I just need to find a way to break my latch when they want to start during the 45min time using the same start PB...like a flip flop resart.

Can you just use a stop button man? Flip flops are nice, but really complicate things when you are doing a flip-flop. It will save you from needing 2 more relays.
 
Can you just use a stop button man? Flip flops are nice, but really complicate things when you are doing a flip-flop. It will save you from needing 2 more relays.

If it was up to me I see no issue with using the stop pb, its kind of the spec though. I can't picture how this would work with relays. An impulse relay would require pulse to latch, pulse to unlatch, pulse to relatch. So basically have to press start twice to reset the circuit not much different than pressing stop then start.
 
I don't know that I will be using it but I am pretty interested in figuring out this flip-flop circuit using just a NO momentary PB and relays. Got a few dozen sketches now but nothing that would work, any pointers?
 
Hv42fQI.jpg


sorry it is huge and sideways, but give that a try. Two relays and two sets of NO contacts on a NO momentary pushbutton.

there fixed it up for ya

There would be bit of issue with that, just so you know. You would have unpredictable behavior on the second relay and would want a time-delay of some sort in there to prevent the power from going to the second set of R1 NO contacts, but that is the basic idea of how the circuit would work with ice cube relays.
 
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