Need help please to work out relay

Discussion in 'General Electronics Chat' started by Hurdy, Sep 3, 2008.

  1. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
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    0
    Hi everyone,

    firstly thank you for taking the time to read this.
    I need to replace a relay in a locomotive battery charger.
    The only problem is, is that the relay has no ratings written on it at all. The relay is just blank.

    It's a plug in relay that has 8 pins in a circle that mount into a holder.

    How can I find out what the rating of the relay is? or is it a case that I have to work back the electronics that plug into it?

    Thank you again for your time,

    Rob
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    If there are no markings, and no documentation is available, the only remaining option is to analyze the circuit it came from. Be sure to choose a replacement with at least 120% of the rating needed.
     
  3. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Hi,

    Thanks for your reply. I've attached a diagram of the relay setup along with the TRIAC PDF that hooks up to the relay.
    Does anyone know what rating relay would suit this?

    Thank you,

    Rob
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    See the attached for a typical internal wiring diagram for an octal relay.
    That's what they're generally called here in the USA, but seeing as the UK and the USA are separated by a common language, there's no telling what you blokes over there might call 'em. ;)
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Rob, there certainly are a lot of pieces missing from that schematic you posted, like which terminal of the TRIAC is which, the correct numbering of the pins on the relay, where the other relay connections go to, etc.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Rob, what do the rest of the relay pins connect to?
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    One problem is that octal relays are not all DPDT.
     
  8. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Hi guys thanks for your reply.
    The relay has no other connections to it. That's it just 3 of them. As for the TRIAC it's not clearly labelled what their pins are on the component but I'll try and work it out and get back to you on it very shortly.

    Thank you for your input so far, it's very much appreciated.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    I question the nature of the device. A relay needs two leads to the coil, and two more for contacts. Even if it's set up to be self-latching, it's still four connections.
     
  10. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    ok guys I've updated the diagram with the TRIAC pin numbers and attached it to this post.

    The application is for a railway locomotive battery charger. My father is part of a railway enthusiasts group and he asked me to try and replace the relay.

    PLEASE IGNORE THE RELAY PINS ON THIS DIAGRAM I'VE GOT PINS 1 & 2 THE WRONG WAY AROUND.
    A NEW DIAGRAM IS POSTED AGAIAN IN THIS THREAD.
     
    Last edited: Sep 4, 2008
  11. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    The POT is used to limit the current as not to over charge the battery.
    I guess it's some kind of trip off device setup if the current being pulled is too high.

    I don't really understand the operation of a TRIC well enough to understand what is going on with this setup. I've tried googling for a guide but no luck as of yet.

    Also are all pins labelled 1-8 standard throughout all plug-in relays? if so then from that we should be able to work out what the coil raiting is and what the contact raiting is. Like you said I always assumed a relay needed 4 connections, 2 for the coil 2 for the contact. Maybe the relay acts as a switch that when the relay magnetizes enough i.e. the current being pulled is to great it just creates an open contact and protect the rest of the equipment.
     
    Last edited: Sep 4, 2008
  12. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    New diagram with Relay pins updated.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Where does the battery connect? After the xfo?
     
  14. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Upon reflection, I don't think the 8-pin package contains a relay at all. I suspect it contains a diac and a capacitor...

    choochootrain.jpg

    I suggest attempting to open the "relay" package to see what is actually inside it.
     
  15. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    oh you might be right. I've never seen a capacitor package like that before.
    I'll open it up and see what it is. Thank you.

    As for the battery it plugs in later on in the circuit which I haven't drawn once the AC has been rectified to DC.

    Thank you for your suggestions it's much appreciated.
     
  16. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Well you're right it's not a relay. I finally had a reply from the guys who made the charger and they said it's not a relay it's a control module. They're going to send me a new one.

    Learn something every day don't you.

    Thank you very much for your help that goes to everyone. I really appreciate it.
     
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