Daisy chain relays?

Discussion in 'Technical' started by AppMaverick, Mar 23, 2014.

  1. AppMaverick

    AppMaverick Member

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    Can I daisy-chain relays? Run power from the battery to a relay and then from that relay to the next, ect? Same with the switch wire... Or do I have to run a virgin wire for each one?

    They will all turn on from the ignition switch...
     
  2. mercgt73

    mercgt73 Member

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    Depends on your loads and number of relays.

    Give us a better idea of what you are trying to do.
     
  3. Krazy Comet

    Krazy Comet Tom Supporting Member

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    Depending on application they usually should have their own power supply from battery, but no reason they can't be triggered by a single wire from ign switch...
     
  4. mav1970

    mav1970 Bob Hatcher

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    If you think about it, most of today's main circuit breaker boxes and under hood engine management boxes contain multiple plug in relays and those boxes are only fed by some sort of main cable from the battery. I think the load would just determine what gauge the main feed cable has to be - in your case a wire just needs to come off the ignition "on" to just trip the relays :)
     
  5. AppMaverick

    AppMaverick Member

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    It would be an electric fan, electric choke, ignition coil. Supposed to have 12v to these things and currently choke and coil are only getting 6v.

    Thought about maybe one relay going to a little fuse box for each of the things to branch off of... But not sure if I would need bigger than a 30 amp relay for that.
     
  6. mav1970

    mav1970 Bob Hatcher

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    I'm picturing a small box containing separate relays for those 3 (or more) items that you mention being all fed by a single large enough power wire to feed those accessories when all are running - then I can only see the need for 1 output wire at the "on" side of your ignition switch being needed as a trip for those accessory relays :)
     
  7. mercgt73

    mercgt73 Member

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    Personally, I would give the fan its own feed and relay. It is a significant load compared the choke and coil. The fan relay needs to support the current that fan will draw. When it comes on, there will be a noticeable drop and you do not want your coil suffering from that. The choke and coil could use the same relay.

    As far as the signal wire goes (IGN on), you could use a single wire for both the relays.
     
  8. rthomas771

    rthomas771 Member

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    Here is the schematic on my cooling fans, water pump, headlights on my Falcon. Instead of running 4 hot wires over to the battery, I have a junction box close to the relay bank that feeds the relays.

    [​IMG]
     
  9. Krazy Comet

    Krazy Comet Tom Supporting Member

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  10. AppMaverick

    AppMaverick Member

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    Ok. So concensus seems to be that I use some sort of junction box for power to each relay, but independant relays - especially for the fan. But that I can use the single ignition wire as a trigger split across all the relays (Can I use the 6v resisted wire that's already there for this, or should I re-run the ignition separately to the junction block like Jeff's appears to be in the diagram?)

    You guys think I can use the pictured fuse box as my junction and breakers all in one? I'd mount that near the battery and have about 6 of the pictured relays for gear (Fan, choke, coil, headlights, horn). That would be the 6 slots on the fuse box I think...
     

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  11. mercgt73

    mercgt73 Member

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    Re-run a 12V IGN ON circuit. You will want to wire the coil side of the relays in parallel so that each coil gets a 12V signal. This, of course, assumes you are using 12V 'automotive' relays.

    If you want some more guidance on calculating current requirements, relay sizing, etc, just ask. I do not want to get too deep here if you don't want to. Jeff's diagram is a great source and sounds like exactly what you are trying to do.
     
  12. AppMaverick

    AppMaverick Member

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    I guess my confusion lies in that on our cars (idk how the falcon is) there is power coming from somewhere to the ignition switch. Then there is the resistance wire (dropping it to 6v) going from the ignition switch to the coil.

    My question would be.. Do I just extend the 6v resisted wire to act as a trigger for the relays getting 12v from the jumction box (in my case fuse box), or should I be running a fresh wire from the junction box to the ignition switch and then a fresh wire from the ignition switch to either the relay or the coil?
     
  13. mercgt73

    mercgt73 Member

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    I think you are confusing the implementation of the relay. A relay has 2 sides, a contact (or switched) side and coil side. The coil side controls the switched side. This allows the relay to use a low current source (such as an ignition switch) to control a high current load (such as a fan).

    So, for you, you want to control the coil side of the relay using a 12V KEY ON (low load) circuit so that the switch side of the relay can connect a 12V source to a 12V (high load) fan.

    If you use the 6V resistance wire, then the coil side of the relay will only "see" 6V (or even less). Well, if the relay is expecting a 12V source, then it will not operate properly.

    Does that make sense?

    Your relay should have markings or specs on the box that tell you the operating voltage of the coil side (6V, 12V, 24V, etc) the coil side current load (20mA, 40mA, etc), and the max current allowable of the switch (or contact) side (10A, 20A, 30A, etc).

    As an example, you can use a 12V 30mA (that is 0.030A) relay to control a 30A fan. How nifty is that?

    To answer your question, you can use the existing 12V KEY ON circuit (yellow wire?), splice into it and extend it into the engine bay, and use that to signal your relays. BUT you NEED TO MAKE SURE that your source is also 12V during crank, or your solenoid will not be operating.
     
    Last edited: Mar 24, 2014
  14. mercgt73

    mercgt73 Member

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    Also, other questions come up:

    1. Are you trying to feed a stock coil with 12V? It was not designed for that...
    2. Is your electric choke designed to operate at 12V?

    Jeff's diagram uses 12V loads (fan, waterpump, headlights). Just want to make sure you don't fry anything.
     
  15. mojo

    mojo "Everett"- Senior Citizen

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    I think he wants to keep the original ign coil feed (6v+ wire) on/to the coil and wants to also trigger ganged relays frm the 6v+.
    I wud also use a 12v source to trigger those relays. I had my elec fan relay triggered by 6v source a few years ago and it got to a point where it wud not get enough volts to trigger that relay. Had to go to a 12v source and have not had any other issues.
     

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