Single Push Button Control

Can you tell us a little more about your application ?

Anyway, here is what is called a '2-wire' control for a motor. You can use the PB instead of the float switch as shown. As long as the PB is help pushed, the supply will be available to the load.

However, for motor control, it is more common to use the '3-wire' control.

If you use 2-wire or single push button system for the start and stop of the motor, the push button will have to be different than the ones used for 3-wire system. In the single push button system, the push button should be toggled for maintaining and releasing the contact for every alternate push action for the button. I would suggest you to use the single on-off switch instead of single push button switch.

See this link:

http://www.danfoss.com/NR/rdonlyres/8ADD5B52-74B5-4AC7-805F-00E490681D7F/0/waterlesson1.pdf

- MS

"Can you tell us a little more about your application ?"

Don't you mean "Can you tell us a little more about your application homework assignment?

Antiquo,

Tell your professor that you need more details of the restrictions. i.e. what kind of push button, what kind of relays are you confined to etc.

If there are no restrictions, then the simplest answer is to get a mechanically toggled push button, one that changes and maintains it's state when pushed once, then returns to its original state when pushed again. These are ofen called Push-On / Push-Off push buttons, or Toggle Push Buttons etc. A variation is a Push-Pull button where to reset to its original state, you pull the mushroom head button back out again.

If he insists that you are limited to one momentary push button, but any kind of relay, then you can use a "Latching Relay" to do this. The button closes the Latch coil through a N.C. contact of the same relay and a N.O. contact of the relay powers the load. Then another N.O. contact feeds the push button circuit to the Unlatch coil but since the N.C. contact is now open, you have avoided a conflict.

If you are limited to a momentary button and no latching relays, you can create a similar circuit to the latching relay, but it requires tow relays and what are called "Late Break" contacts in one of them. An alternate version is to make one of them a timer.

If he further restricts you to not allowing this special function, then it cannot be done.

This is commonly referred to as a "toggle on - toggle off" function and is commonly used in PLC ladder logic programming. As was previously stated there are mechanical switches that can perform this function. However, using a simple momentary push button is more difficult. It is easy to latch the relay ON but it will require a second relay to break the latch. The problem is that when the second relay breaks the latch, the first relay sees the push button contacts and turns on again.

What is needed is what is called a "one shot" relay. This type of relay turns on when current is applied then after a set time turns off with current still applied. It can only be turned on again after the current is removed. I will leave it up to you to figure out how to incorporate a "one shot" relay into your circuit.

(conventional wiring diagram of a single push button to function as start and stop using relays?)

Hi sir, good morning to all.

In this thread, I'll be using One (1) Normally open, momentary push button controlling relays to start /stop control. I know this can be done in PLC but I need a conventional wiring.

Thanks to all

A long time ago I once hooked up three relays and a pushbutton so that successive presses of the button would cycle the relays 1-2-3-1-2-3 etc. I have forgotten what combination of NO and NC relay contacts can achieve this. You might need to look at make-before-break or make-after-break configurations.

Another option is a type of relay sometimes described as an alternator.

I will try to recall the details, but no promises.

I can help you just via programming with Ladder Diagram.We apply "Single Shot Pulse"or "one shot" as a friend described above, so tell me if you like,.............

Thank you very much Ali18, I have done it also on my aplication in one of my projects in PLC. All I need is conventional wiring.

Best Regards

Hi Yes you can use a single push button as a start / stop control using a relay.

The relay you need to use is called a "Set/Reset" relay. On the first press action the relay is set, and on the second press the relay is reset, but this is a special relay.

These relays are avialiable of the shelf from some suppliers.

Cheers

Joe

Ahhh.. nostalgia

Reminded me of a 'mechanically latched lighting control contactor' designed by my team way back. One push of the button energises the contactor magnet, which then stays mechanically latched. A second push of the same button releases the latch, and the contactor becomes Off. Image from US patent 6628184

If you want to use it for equipment like tools or other equipment where safety is important, simply DON'T.

Use a dual button green and red system with the start green button recessed and the stop red button big and difficult to miss even with your eyes closed....

Also I am pretty sure that most conventions for tooling (if that is what its for) do not allow a single button.....its simply too dangerous.

But as you never told us what it was for.........

"But as you never told us what it was for........."

Because if he tells us it is a homework assignment, he fears he will not get the answer he needs...

Let me help you.i cant draw the circuit here but i hope you understand my english.i hope you are good with DOL starter. Now put the start button in parallel to the control relay in DOL. Here with main contacts we want an EXTRA contact. Now when you press the button an output of main contact hold the control relay so that 3 phases and one EXTRA switch is close now.connect that EXTRA switch in series with thermostat and push button.Replace the thermostat with another NC-relay. now you press it again to short the NC-relay placed instead of thermostat to break the circuit. (hope now you understood) -Hit

This one works but it is not very practical. There are easier and cheaper ways of doing this. (Three wire control)

This could posibly be used for a two pump system that uses pump one the first time and pump two the second time.

Elroy

Thank you all guys, sorry for late response due to work pressure. Thanks also to Elroy, yes this is not practical & as I've analized your circuit, CR4 & CR5 timely be switch on. Guys, this is neither a homework nor a school project, this is just an alternative wiring as to which spare I have in hand just to run the circuit (temporary wiring) for I nkow its not practical. Also 'am curious on having this conventional wiring as compared to PLC logic which I did in my other application. I supposed to insert ladder logic but the server I'm using prohibits using URL.

Thank you all guys.

Best regards,

Antiquo

It's cheaper to have spare parts to hand rather than to incur the effort needed to frig the wiring and frig it back again afterwards. No Electrician would countenance doing it with a single <...push button...>.

Google "bistable pushbuttons". A pushbutton that has a mechanical bistable arrangement inside it doesn't really need a <...wiring diagram...> or <...relays...>, as it's equivalent to a simple toggle switch. However, question the need. The reason for using a push-to-make button to start and a push-to-break button to stop, and an interposing relay to store the "started" condition is that, were the power to fail for whatever reason, then the circuit drops out and there is deliberate intervention to restart - which is a safety issue.