Relays

Discussion in 'General Electronics Chat' started by Ringojames, Nov 27, 2013.

  1. Ringojames

    Thread Starter New Member

    Nov 27, 2013
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    Hi guys,

    I'm new to your forum (i stumbled across it searching the web and it looks a really helpful place!)

    I'm after some help regarding DC relays, automotive relays, I understand the basics of relays, but I am now trying to take my knowledge a step further how they work when you have more than one connected together (what applications would use this, how this works etc) I've tried browsing the web and you tube but am only finding basic relay info

    I really hope you can help me or direct me to somewhere I could get clued up. (Diagrams too would make it a WHOLE lot easier for me to understand)

    Thank you for your time
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    A relay is an electromagnet with a set of contacts that operate when the voltage is applied.
     
  3. Jony130

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  4. strantor

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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    QUOTE=Ringojames;670987]but I am now trying to take my knowledge a step further how they work when you have more than one connected together (what applications would use this, how this works etc) I've tried browsing the web and you tube but am only finding basic relay info
    [/QUOTE]

    Before the prevalence of solid state control and PLC's, industrial control was carried out with (Google) relay logic, this usually consisted of very large electrical cabinets full of electromagnetic relays and wired to perform all the logic which is based on (Google again) Boolean Logic.
    e.g. http://static.schneider-electric.us/docs/Machine Control/0140CT9201.pdf

    Max.
     
  6. Ringojames

    Thread Starter New Member

    Nov 27, 2013
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    Hi thanks for the replies, like I said I understand the basic principles of a relay on its own but I can't get my head round what type of application you would need more than one linked in the same circuit, because the only times I've seen them is on basic tuition wiring diagrams where it shows a relay operating a horn or a motor. I can't find any info on "the next step up" if you like where there are two or more relays introduced to a circuit. I hope that makes sense?? (Sorry if I've rambled on a bit)

    Thanks for the links ill spend some time reading them.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The links should offer a bit of insight, and if necessary do a search for PLC ladder logic, as this is the direct descendant of relay logic and is usually portrayed in the same format.
    In automotive use, it is usually rather a simple single relay operation, although the exception is where a contact on one relay will interlock another, this again is simple Boolean logic, AND, OR, NOT, etc.
    If you scroll down to the lower part of the PDF, you will see the logic portrayed in common ladder format.
    For automotive, study the service manual schematics.
    Max.
     
    Last edited: Nov 27, 2013
  8. inwo

    Well-Known Member

    Nov 7, 2013
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    A simple example that comes to mind.

    Two small switches each controlling a relay. In turn each relay powering a high current motor. (that's a basic use of a relay often called a motor starter or contactor)

    Both motors running at the same time may not be allowed.

    The coil of relay #1 is fed thru the normally closed contacts of #2.

    The coil of relay #2 is fed thru the normally closed contacts of #1.

    Then whichever relay is "in" prevents the other from pulling in.

    Called interlocking in relay logic.
     
  9. Ringojames

    Thread Starter New Member

    Nov 27, 2013
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    Thanks for all the info and quick replies! I've got quite a bit to go on there guys! Nice one
     
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