I suggested the reasonable scheme for doing what the TS requested in post #1, in a manner that will perform reliably, in post #11. That was based on the guess that the system had to be reliable and last for some extended period of time. The interval timer and suitable motor control relay are both made by OMRON, a company with fairly wide distribution, and reasonable prices.
Given, however, that we have no information as to the actual application, which there may be a better scheme to achieve the desired control, such as a level switch or a pressure switch, operation of alternative timers is all that has been suggested.
A 555 could do the job, the capacitor choice is limited to the very low leakage variety of capacitors, and the supply voltage would need to be regulated fairly well.

 

a relay or contactor of some as yet unknown capability.

The circuit shown in post #1 includes a picture of a relay that may work for a few cycles. then the contacts will fail. They are not rated for 220 volt service.

I think I said that already.

we would need to know the startup current or the stall current of the motor in order to recommend a suitable relay or contactor.

Gosh Bill, You and I are not the only ones who said this.

If we knew more about why You are pursuing this project,
and more details about your Pump and what it's supposed to do,
You might get a more detailed response,
or even a completely different way to solve the problem.

{Blue Bold Italics inserted into LowQCab's post #5}

Is this personal? Why pick at me and not others?

I agree. We need full details. And it's been just a few days since we heard from the TS. We have no idea if he's lost interest in this project or even if he's followed someone's advice and bought a timer controller like that which has been suggested by someone before now.

 

Hi guys
I want to make an automatic on off switch with 555 timer , i want to use it to power on my 220ac water pump for 20 minutes , and turn it off for 5 minutes .
I found this circuit :

Https://www.circuits-diy.com/wp-content/uploads/2020/07/Automatic-ON-OFF-Relay-Circuit-768x432.jpg

But it need a modification to work fine with my time .
Please help me guys and thank you

In theory.....
For T = 25 mins
F = 1/T = 1/25 = 0.04 s

where:
tc = 20s
td = 5s

assuming a capacitor of 100uF
Rb = td / ( C x ln(2) ) = 5 / ( 100*10^-6 x ln(2) ) = 72.13kOhm

and
Ra = tc / ( C x ln (2) ) - Rb
Ra = 20 / ( 100*10^-6 x ln(2) ) - 72.13*10^3 = 216.4kOhm

 

OK, the proposal in post #23 is interesting. The real-world implementation is the challenge. Bob Pease was always the person to bring up that reality in circuits. The problem is that real 100 Mfd capacitors are far from perfect. First, there is voltage dependent leakage of the charge, end then in addition there are charge storage and charge recovery variables that tend to have effects.
What all of this reduces to is that the actual capacitor to deliver the required times reliably will take some effort. And in addition the power supply will need to be very stable and low noise.

What will be interesting is to see what results the TS achieves with that published circuit. I don't recall just what the original complaint was, other than "it did not work fine" for the longer time periods.

We do not even know if the TS actually assembled that circuit and tried it.

 

Why not look at the graph of a timer in the 555 datasheet?
It shows a time of only a couple of seconds with your calculated 100uF and 72k resistor.
The graph shows you need about 1000uF and an 8M resistor:

 

Why not look at the graph of a timer in the 555 datasheet?
It shows a time of only a couple of seconds with your calculated 100uF and 72k resistor.
The graph shows you need about 1000uF and an 8M resistor:

AG correctly describes the problem, since most 1000uF capacitors are electrolytic types that are subject to all of the flaws that I mentioned. And an 8 megohm resistor can easily be created with a few lower value resistors, but at that level assorted leakage problems will be likely. So my suggestion will be to start experimenting with a 470 mfd capacitor and a 4.7 megohm resistor, both easily available and cheap.
Of course, this is presuming that the TS is actually going to assemble the timer circuit.

 

Has the TS (Thread Starter) lost interest? Haven't heard from the TS since Sunday and here now it's Friday.