Switches - PLCS.net

jayshah11 · February 24th, 2003, 05:38 PM

When a repaly is connected across a START switch in general ladder diagrams, what does it exactly signify?

When START is pressed, its a momentary press. And then the relay gets energised and the current flows continuously till the stop swich is pressed.

I am wondering if my understanding is right or not.

Jay

rsdoran · February 24th, 2003, 05:47 PM

You have the gist of it. What happens when you press a normally open pushbutton (used for start pushbuttons normally) is that power flows to the relay "coils" to energize them which in turn will close the Normally Open contacts on the relay which on one side is connected to the same power as the pushbutton and the other side is connected to the relay coil, this holds the coil latched.

I need to display this too.

rsdoran · February 24th, 2003, 08:45 PM

http://electronics.howstuffworks.com/relay1.htm

Steve Bailey · February 25th, 2003, 06:16 AM

jayshah11,

You might want to take a look here:

http://users.adelphia.net/~sbailey2/Relay.htm

I put these pages together to teach myself a little about html and javascript. No popups either.

Be sure to click on many of the objects to animate them.

Tom Jenkins · February 25th, 2003, 09:06 AM

This arrangement is often referred to as a "holding circuit", and the relay contact in parallel with the switch is referred to as a "holding contact" because the relay holds itself on. Get familiar with this circuit - it is used for all kinds of control logic from hardwired motor starters to PLC programming.

PS Steve - neat demo!

seppoalanen · February 25th, 2003, 11:48 AM

Some people use turnable selection switches where have many contact whoes make connections in diffrent positions. Push-Buttons are allways in right positions and we can't forget them to wrong positions. Result of many yers thinking !

Danocane · February 25th, 2003, 11:49 AM

You can find some examples of Motor Start/Stop controls at this site:

Basic Motor Control Schematics

PS Mr. Bailey very well designed and informative web pages.

Thanx Dan

rsdoran · February 25th, 2003, 07:12 PM

This is a competition isnt it?

February 25th, 2003, 09:01 PM

very good

PLucas · February 25th, 2003, 09:30 PM

Ron

I like your animation, it does illustrate a retaining circuit quite well, the only thing that concerns me is that you have your start button, stop button and contactor coil across 2 phases, on this side of the pond that is 415v and as you are probably aware that would be a no no!

Paul

P.S I am not trying to criticise in anyway, you just might get some numb-nut go and wire a circuit like that.

rsdoran · February 26th, 2003, 06:03 AM

For the purpose of the display it was easier to show using line voltage. This is still a very common practice depending on situation. I prefer using 24vdc or at the most 120vac but it can and is done with line voltage.

February 24th, 2003, 05:38 PM	#1
jayshah11 Member Join Date: Feb 2003 Posts: 23	Switches When a repaly is connected across a START switch in general ladder diagrams, what does it exactly signify? When START is pressed, its a momentary press. And then the relay gets energised and the current flows continuously till the stop swich is pressed. I am wondering if my understanding is right or not. Jay

February 24th, 2003, 05:47 PM	#2
rsdoran Lifetime Supporting Member Join Date: Apr 2002 Location: Birmingham, AL Posts: 7,372	You have the gist of it. What happens when you press a normally open pushbutton (used for start pushbuttons normally) is that power flows to the relay "coils" to energize them which in turn will close the Normally Open contacts on the relay which on one side is connected to the same power as the pushbutton and the other side is connected to the relay coil, this holds the coil latched. I need to display this too. __________________ http://www.patchn.com Industrial Electrical & Maintenance @ www.patchn.com "Tell me and I forget, show me and I remember, involve me and I understand."

February 24th, 2003, 08:45 PM	#3
rsdoran Lifetime Supporting Member Join Date: Apr 2002 Location: Birmingham, AL Posts: 7,372	A graphical view of how a relay works http://electronics.howstuffworks.com/relay1.htm __________________ http://www.patchn.com Industrial Electrical & Maintenance @ www.patchn.com "Tell me and I forget, show me and I remember, involve me and I understand."

February 25th, 2003, 11:49 AM	#7
Danocane Member Join Date: Aug 2002 Location: Topeka, Kansas Posts: 79	RE: Relay Control Info. You can find some examples of Motor Start/Stop controls at this site: Basic Motor Control Schematics PS Mr. Bailey very well designed and informative web pages. Thanx Dan __________________ There is One Firearm for every 12 people in the world. My question is: How do we arm the other 11?

February 25th, 2003, 07:12 PM	#8
rsdoran Lifetime Supporting Member Join Date: Apr 2002 Location: Birmingham, AL Posts: 7,372	OK I admit I was jealous This is a competition isnt it? __________________ http://www.patchn.com Industrial Electrical & Maintenance @ www.patchn.com "Tell me and I forget, show me and I remember, involve me and I understand."



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February 25th, 2003, 06:16 AM	#4
Steve Bailey Lifetime Supporting Member + Moderator Join Date: Apr 2002 Location: The boondocks of Western Massachusetts USA Posts: 4,664	jayshah11, You might want to take a look here: http://users.adelphia.net/~sbailey2/Relay.htm I put these pages together to teach myself a little about html and javascript. No popups either. Be sure to click on many of the objects to animate them.

February 25th, 2003, 09:06 AM	#5
Tom Jenkins Member Join Date: Apr 2002 Location: Milwaukee, WI Posts: 4,957	This arrangement is often referred to as a "holding circuit", and the relay contact in parallel with the switch is referred to as a "holding contact" because the relay holds itself on. Get familiar with this circuit - it is used for all kinds of control logic from hardwired motor starters to PLC programming. PS Steve - neat demo!

February 25th, 2003, 11:48 AM	#6
seppoalanen Member Join Date: Jan 2003 Location: Finland Posts: 1,024	Some people use turnable selection switches where have many contact whoes make connections in diffrent positions. Push-Buttons are allways in right positions and we can't forget them to wrong positions. Result of many yers thinking !

February 25th, 2003, 09:01 PM	#9
guest Guest Posts: n/a	very good

February 25th, 2003, 09:30 PM	#10
PLucas Member Join Date: Apr 2002 Location: Gillingham Kent Posts: 1,743	Ron I like your animation, it does illustrate a retaining circuit quite well, the only thing that concerns me is that you have your start button, stop button and contactor coil across 2 phases, on this side of the pond that is 415v and as you are probably aware that would be a no no! Paul P.S I am not trying to criticise in anyway, you just might get some numb-nut go and wire a circuit like that. __________________ There are 10 types of people in this world.. Those who understand binary and those who don't!

February 26th, 2003, 06:03 AM	#11
rsdoran Lifetime Supporting Member Join Date: Apr 2002 Location: Birmingham, AL Posts: 7,372	For the purpose of the display it was easier to show using line voltage. This is still a very common practice depending on situation. I prefer using 24vdc or at the most 120vac but it can and is done with line voltage.

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