I have a client that has an equipement in an area where sometimes electricity goes on and off many times a minute , and it can dammage his equipement, so he asked me for protection system that works as following:

1- the system needs to starts with an ON button (on button or push button or whatever)

2- if the power goes off the system will shutdown (that is normal)

3- But if the power goes on again, the system will not start automaticly

4- it needs some sort of timer, that will check if the electrity was back for 5 mins for example without any cut again to start the system

5- and of corse an OFF Button.


Thank you


This is a very simple thing to do with a small microcontroller. The on and off buttons would be just inputs to the micro. The micro would sense AC power via a opto-coupler and control a relay that switches the AC on/off to the equipment. Even a small PIC with internal oscillator can do this easily.

Of course if your client can't even afford a "smart relay", then he can't afford to pay you to create something different. This kind of client is way more trouble than the little profit you might make. He'll always be trying to push you on price, and second guess everything you're doing thinking you're trying to take him for a ride. Run away.

  • \$\begingroup\$ I have a feeling that "client" really means "my brother" or something. \$\endgroup\$ – pipe May 27 '16 at 11:54
  • \$\begingroup\$ Im not gonna accept money from him btw, im just trying to help him out. \$\endgroup\$ – KADEM Mohammed May 27 '16 at 12:14
  • \$\begingroup\$ The microcontroller would need some sort of backup power supply. Further, reliability and safety are more difficult to ensure with a DIY solution, which is worrying when equipment (or human) safety is being considered. \$\endgroup\$ – user2943160 May 28 '16 at 4:37

Your client needs a start-stop contactor and timer.

enter image description here enter image description here

  • Press the green button to switch on power.
  • When power goes off contactor will drop out.
  • When power comes back on start the timer.
  • When time reached press green button.
  • It has an off button too.
  • \$\begingroup\$ Still you need to manually start again ! \$\endgroup\$ – KADEM Mohammed May 27 '16 at 12:41
  • \$\begingroup\$ That was one of the requirements: "But if the power goes on again, the system will not start automaticly (sic)." Also: "1- the system needs to starts with an ON button." \$\endgroup\$ – Transistor May 27 '16 at 12:45
  • \$\begingroup\$ No i want the system to automaticly start if the button is ON and the power was back for 5 mins without cutting again...otherwise it will reset the counter to 0 ! \$\endgroup\$ – KADEM Mohammed May 27 '16 at 12:54
  • \$\begingroup\$ You need to fix your question then. How do you think you will do this without a "smart relay" or a timer and dumb relay? \$\endgroup\$ – Transistor May 27 '16 at 12:55
  • \$\begingroup\$ Well this is the question i knpw how to make it with a zelio, the guy said : can't you do it with somethg simpler...so here i am asking ! \$\endgroup\$ – KADEM Mohammed May 27 '16 at 12:57

What you need is the Direct on line starter with timer. Since nothing is free in this world and everything comes with a price, get your "client" to agree to buy for you the simple starter with red+green push buttons on it and get it linked to the timer unit.

This starts the load with a momentary press on the green button and it drops the load off during power failure. When power restored, the timer runs and when it is up to 5 minutes, the timer shorts out the contacts of the green button, ensuring the automatic self start.


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