You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old December 15th, 2013, 10:36 AM   #1
indel99
Member
United States

indel99 is offline
 
Join Date: Dec 2013
Location: Sour Lake
Posts: 4
Stop light

To start/stop energizing the heating elements there are used two buttons, each with a NO and NC contacts. The push buttons have LED lights (a max of 15 mA). There is a set of power contacts, for the heaters, that are driven by a coil (240Vac), CR1. The start button will actuate the coil, the stop button will interrupt the heating. The general 240Vac supply is separately provided.
There is only one low power NO contact, physically connected on the contactor driven by CR1 (besides the power contacts).
There are not other contacts to be switched by a coil.
Stop red button is glowing while the heaters are not energized.
Start green light will glow when push button start is pressed.
With only NC NO contacts, stop button light cannot be cut.
There is a way, connecting stop button LED combination between L1 the CR1 coil and L2.
It works, I tried several times. What would be the CONS to this wiring?

L1 LED coil (800 Ohm) L2
X-------------XX--------------------xCR1x----------------x

The LED 15 mA are more than an order of magnitude less than the necessary current to the coil to be energized, and the drop of voltage on the coil is less than 15V, so the voltage on the LED still, would be over the minimum of 195Vac, necessary to lit the light.
  Reply With Quote
Old December 15th, 2013, 12:59 PM   #2
Lancie1
Lifetime Supporting Member
United States

Lancie1 is offline
 
Lancie1's Avatar
 
Join Date: Jul 2003
Location: Alabama
Posts: 10,002
The wiring you described would look like this. However I would not depend on it to always work. I would add another 240-volt coil relay with one or two double-throw contacts for the LED lights.
Attached Images
File Type: jpg Heater Schematic- Indel99.jpg (32.1 KB, 108 views)
  Reply With Quote
Old December 15th, 2013, 06:21 PM   #3
indel99
Member
United States

indel99 is offline
 
Join Date: Dec 2013
Location: Sour Lake
Posts: 4
Stop light

Yes, that's the wiring. It works for LED combinations, not for incandescent lights or others, requiring a larger current. The current for those lamps is 15mA max. The drop of voltage caused by the 15mA is less han 10% of the 240Vac, and the minimum voltage for the lights is 195Vac.
My question was related to any regulations, which I didn't find, against.
Thank you for answering.
BTW, I do not claim any rights, anybody is invited to use it, it saves a relay coil.
  Reply With Quote
Old December 15th, 2013, 09:47 PM   #4
Mickey
Lifetime Supporting Member
United States

Mickey is offline
 
Mickey's Avatar
 
Join Date: May 2003
Location: Palmdale,Ca
Posts: 10,132
I don't know about code or regulation violations but it just seems wrong to me.


I would replace CR1 with something that has a NO and NC contacts and connect the red led to the NC contacts upstream of the red led. Then connect the red led's neutral to X2.
__________________
Mickey

If you want happiness for an hour-take a nap. If you want happiness for a day-go fishing. If you want happiness for a month-getmarried. If you want happiness for a year-inherit a fortune. If you want happiness for a lifetime-help someone else.
----- Chinese Proverb

Last edited by Mickey; December 15th, 2013 at 10:04 PM.
  Reply With Quote
Old December 16th, 2013, 07:31 AM   #5
bernie_carlton
Lifetime Supporting Member + Moderator
United States

bernie_carlton is offline
 
bernie_carlton's Avatar
 
Join Date: Apr 2002
Location: Yakima, Washington
Posts: 6,248
I'm concerned about the 'OFF' LED shorting. I don't know if they can fail that way but just in case.
__________________
Controlling outputs is the PLC's way of getting its inputs to change.

www.thePLCguy.com
  Reply With Quote
Old December 16th, 2013, 08:55 AM   #6
OZEE
Member
United States

OZEE is offline
 
Join Date: Mar 2006
Location: Kansas
Posts: 1,695
Will it work?? Maybe...

But just because you can isn't a reason to do so. Forever, anybody that would look at it or who would be required to work on it would think "WTF was indel99 thinking?" -- but only for the few minutes that it would take them to install the typical relay.
__________________
"I wonder how people did this before the days of PLCs?" If people would take the time to learn how a simple relay control circuit works..... [Helliana]
  Reply With Quote
Old December 16th, 2013, 09:14 AM   #7
indel99
Member
United States

indel99 is offline
 
Join Date: Dec 2013
Location: Sour Lake
Posts: 4
stop light

To Bernie
Righto!
If the LED fails - short, that's poor engineering! The CR1 would be energized when it is not required!
The LED "complex" consists of a series resistor, with two, back to back, LEDs, so they will light on both alternances of the 240Vac.
Whatever is in series with the LEDs, must dissipate some 3.4W.
Now, a LED fails on overvoltage, and that is melting its junction, that is an open circuit. If the series element is a metal film resistor, the same, it will be an open, on exceeding ratings.
I have to make sure, I'll try to ask the guys who make the illuminated push button, "what if".
  Reply With Quote
Old December 17th, 2013, 09:17 AM   #8
indel99
Member
United States

indel99 is offline
 
Join Date: Dec 2013
Location: Sour Lake
Posts: 4
stop light

I did dig about the illuminated push button, and there are some excerpts:

Supply voltage limits 195...264 V AC
Current consumption 14 mA
Service life 100000 h at rated voltage and 25 C
Surge withstand 1 kV conforming to IEC 61000-4-5
Product certifications CSA, UL listed
Resistance to fast transients 2 kV conforming to IEC 61000-4-4
Resistance to electromagnetic fields 9.14 V/yd (10 V/m) conforming to IEC 61000-4-3
Resistance to electrostatic discharge 8 kV in free air (in insulating parts) conforming to IEC 61000-4-2
6 kV on contact (on metal parts) conforming to IEC 61000-4-2

Somebody mentioned the "gut filing", and I agree completely. In fact, this is why I wrote to this forum, so the bright minds of automation will put me on the right way.
Well, it is safe to use in "totem pole" two devices between two power supply lines. They are used, a lot, in electronics (my main field of activity)
Therefore, I am going to use the diagram that, Lancie1, so wisely, have drawn for us, from only two words from me.
Thank you, guys, I'll be around.
  Reply With Quote
Old December 17th, 2013, 09:44 PM   #9
Lancie1
Lifetime Supporting Member
United States

Lancie1 is offline
 
Lancie1's Avatar
 
Join Date: Jul 2003
Location: Alabama
Posts: 10,002
I think that how well it works will depend on the coil size, resistance, and voltage as compared to the LED voltage and type. The same LEDs may work for one specific relay or contactor coil, but not work for several others. What if two coils are needed in parallel? How will that effect the operation of the LEDS? It seems that parallel coils will lower the resistance, so maybe the Red LED could glow brightly with coil OFF, but the green LED may not glow when the device is ON.

Will both LEDs glow dimly when the load device is OFF? They could if a small coil happens to have a high resistance.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
MCR circuits required to be hardwired? cisco_kid LIVE PLC Questions And Answers 11 December 20th, 2007 10:09 AM
traffic light again automation.robotics LIVE PLC Questions And Answers 2 April 3rd, 2007 06:11 PM
Can You Help? Buddha LIVE PLC Questions And Answers 6 May 31st, 2005 08:10 AM
related with logic jayesh.monpara LIVE PLC Questions And Answers 31 May 29th, 2005 11:57 AM


All times are GMT -5. The time now is 08:33 PM.


.