Help with mechanical timer relay types

Hi all,

This is actually a personal project, if that's ok. My uncle has some property that has a well, he wants to have the well automatically fill an above ground water storage tank (unpressurized, in the 3,000 gallon range). Of course if you run a residential well too long you can go dry and burn the motor up, so he asked me to come up with a solution.

Here are my current thoughts: single float inside the tank, when it drops it calls the well pump to run (through a contactor) and when the float is high, it stops the pump from running. If the pump is called to run for longer than desired, then it goes into a rest mode. Once the rest mode is done, the pump is allowed to run again. If the float is still not high, the pump will continue to run until the float is sufficiently high. So it might take several run/rest cycles to get the tank filled, but that's ok it's just for irrigation.

Ladder logic wise, it's stupid simple and I drew it out on paper in about five minutes. However, I'm used to programming PLCs where things can be sealed in, there are bits for the timer that are true when the timer is running but still counting, set and reset coils, etc. So I thought hey, I'll go take a look at timer relays and WOW, I was overwhelmed with all the different modes and a seeming lack of common nomenclature. Here's the PDF of the timer I was looking at, it's from Automation Direct and has the following modes:

1 On Delay (seems obvious, relay closes after delay)
2 Interval On (turns on, then off equally?)
3 Flasher - On 1st (no idea)
4 Triggered On Delay (no idea)
5 Watchdog (counter starts when trigger is applied, reset when trigger is reapplied, something like that?)
6 Single Shot (relay closes for a very brief time after counter is done?)
7 Off Delay (relay is closed, opens after trigger is removed when counter is done?)
8 One Shot Falling Edge (relay opens for very brief time after counter is done?)

I was wondering if anyone had a good reference for the various timer relay modes, and if there is any analogous information on how they might compare to timers in ladder logic. Also wondering why the timer has two relays, do they work identically? Finally, is there a way mechanically to have the equivalent of the "active and counting, but not done" bit?

Thanks for any help!

How about KISS, summat like this, industrial and outdoors-rated of course, 30-min on, 15min off; wire a logical AND of its output with the level switch command.

Why not just add a low water probe to the well, to cut the pump out if the water level drops too low? Generally easier to install when the pump is out, then lowered in, but if there's enough space between the casing and the riser pipe you can just drop a wire down. Do need to know how deep the pump is though.

Omron do what they call a floatless level switch, you can use the bore casing as the E electrode and then the probe is just a stainless steel rod with a copper wire attached, and sealed up to prevent corrosion of the copper. Omron sell them too.

Alternatively your timer solution also could work. Use the flasher (equal on, equal off) mode. Have a stop and start float to drive a two pole relay. One pole of the relay paralelled with the stop float as your "hold in" contact. Second pole of the relay enables the timer.

Timer contact energizes the pump contactor coil.

Cant do a drawing right now as I'm on my phone typing this.

Drbitboy That would be a pretty simple solution I agree, but the well pump is 240VAC and draws substantial current.

Some timers feature one or more sets of instantaneous contacts along with the timed contacts.

For those that don't you can parallel a relay with the timer.

defcon.klaxon said:

Drbitboy That would be a pretty simple solution I agree, but the well pump is 240VAC and draws substantial current.

Click to expand...

that was only to present the concept; there are 240v timers, plus if there are relays involved it does not matter what the timer voltage is anyway.


anyway, it's your thing, you'll figger it out I am sure.

For the price of several of those timer relay modules you could just purchase one of their inexpensive Click PLC's and just write the program.

Are you certain the pump doesn't have level and/or thermal protection built in? If not then you might want to design in low level protection, as suggested by Saffa. Check with the pump manufacturer and see if it is an option. No sense taking a chance.

I like drbitboy's suggestion. If you have 240VAC you should have 120VAC. Just install a relay.

For the timer you found, I don't see any good option other than Flasher mode. Your OFF times will be equal to your ON times. Then you might run into run cycle count concerns. You could add a second timer, but now you're approaching mikeexplorer's suggestion.