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2 set o' lights same fuse??

Discussion in 'Lighting' started by comajoe, Mar 24, 2012.

  1. comajoe

    comajoe [OP] Well-Known Member

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    i already have a set of hella 700s, i now want to add another set of hella 700s. i have the original set going to the fuse block under the coin thing.

    can i use the same fuse block slot for all 4 lights?? they are 55w now but i plan on upgrading the blubs to 100w. i have an add-a-fuse thing goiing..can i just add all FOUR lights to that add a fuse? what rated fuse should i use 15W?

    thanks for any help and remember i plan to upgrade to 100w bulbs...
     
  2. Pugga

    Pugga Pasti-Dip Free Since 1983

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    You can use the same wiring as long as all the wiring and the fuse are rated high enough to handle all 4 lights. You should have fairly low gauge wire, especially if you're planning on going with 4-100W bulbs. 4-55W bulbs draw about 19A (Amps = Watts/Volts, 55Wattsx4/12volts), 4-100W bulbs draw about 34A.

    If you're going to use 4-100W bulbs, I'd lose that add-a-fuse thing and go with a 'cleaner' power source. In the under hood fuse panel, there is a threaded pin at the front, passenger side of the fuse panel. That is power directly from the battery so I'd pull power from that. Use your add-a-fuse to control the 'trigger' to the relay. Also, make sure all the components in your system are setup to handle over 30A. Most standard relays are not and do NOT run that kind of power through a standard switch, it won't handle it.
     
  3. comajoe

    comajoe [OP] Well-Known Member

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    your right, i wasnt being very clear. i am using the add a fuse for the switch, what i SHOULD have asked is it OK to use the add a fuse to power both on/off switches? i plan to wire the lights separate from each other with each pair of lights with its own switch. i was gonna run the power lead directly to the battery like the first set, with the switchs getting their juice from the one fuse slot it the under dash block. thanks for the help.
     
  4. Rich91710

    Rich91710 Well-Known Member

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    Add a fuse to a switch that operates a relay.
    You can hang as many lights off of the relay as the relay will handle.

    100w lamps? Don't run more than 2 off of the same relay.

    To add, run two relays, parallel the coils (the add-a-fuse and switch can handle two relay coils). Run each relay on it's own twin circuit with it's own 20a fuse and 10 gauge wire from the battery.

    Or two separate switches... but yes, the single add-a-fuse can handle both switches and relay coils.
     
  5. joes06tacoma

    joes06tacoma Well-Known Member

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    LEER Shell with dome lights operated with 3 way switches, aux backup lights with relay and 3 position switch, modified wiring to compass/temp display and clock to include switch that disables dimming function (poor man's DRL solution), Scan Gauge 2
    X2
     
  6. Pugga

    Pugga Pasti-Dip Free Since 1983

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    :thumbsup:
     
  7. comajoe

    comajoe [OP] Well-Known Member

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    OK you kinda lost me there until the last paragraph, but i think i see what your saying.....a 20A fuse in the add a fuse should do it? thanks
     
  8. Rich91710

    Rich91710 Well-Known Member

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    No....

    Run the aux lights on a dedicated fuse connected to the battery positive or to a high-current tap in the underhood fusebox.

    The wire on the add-a-fuse is not going to be sufficient for a 20a circuit.

    Each pair of lights (if you're running 100w) needs it's own relay.
    Light ground to chassis.
    Light hots to relay pin 30.
    Fuseholder to relay pin 87
    Other end of fuseholder to power source.

    Relay pins 85 and 86 are the relay coil.
    Connect one of them to the chassis.
    Connect the other one to your switch.
    You CAN connect more than one relay to the switch, if for example, you want to operate 4 100w lights from a single switch.

    The other pin on the switch goes to the add-a-fuse under the dash.
    This one can be connected to a circuit that is switched with the ignition or hot 24/7 (just don't forget to turn them off!)

    You CAN feed multiple switches from a single add-a-fuse. Just keep in mind that the fuse is protecting the WIRING... not the device.
    The wire needs to be sized properly to handle at a minimum 40% more than the load.
    The fuse should be sized to no less than 20% more than the load.



    Now... you can ignore this part, I'm including this for others:

    You may have noticed that I recommend connecting the load to relay pin 30 and the power source to pin 87.
    Why did I do this?
    Because not all relays are 4-pin. Many (most in my area) are 5pin.
    If the battery is connected to pin 30, the relay is switching it between pins 87 and 87a. When your switch is off, pin 87a is hot... 24/7.
    If it is not properly insulated and protected, it CAN cause a short.

    By connecting the battery to 87, and the load to 30, the relay is switching the LOAD between 87 and 87a. When the switch is off, the load is connected to 87a. BFD. 87a NEVER goes hot.

    The standard convention of connecting the hot to pin 30 is because many applications will use the relay to switch the hot between two loads... such as low-beam/high-beam, or fog/driving.
    Of course, if pin 87a is properly insulated and/or connected to a load, then it is perfectly safe.

    Yes... Fog/driving ;)
    Want to run fog lights and driving lights in compliance with the law, and only have to add one switch to your dash?
    Run the switch to a relay as normal, then feed the output of that relay to pin 30 of a 2nd relay. Connect pin 87a to the fogs and pin 87 to the driving lights.
    Now connect the coil of the 2nd relay across your high beam socket.
    When the high beams are activated, the 2nd relay pulls in, kills the fogs, and activates the driving lights.
     
  9. comajoe

    comajoe [OP] Well-Known Member

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    thanks for your help and patience....when you say device i assume switch??

    see, under the dash i can find only one open slot in the fuse block that is hot when the ign is on... (hot 24/7 is out for me cause i will forget) that is why i am trying to power two seperate switches from the same fuse slot. i PLAN to upgrade to 100w bulbs but i can deal with stock 55w just fine if that simplifies things. if the wiring for the switch to power that came with the kit isnt enough(i assume its 18 ga) what size should i use to power 2 switches from the same power source to 2 seperate lights? fuse amperage?
    again thanks for the help.
     
  10. Rich91710

    Rich91710 Well-Known Member

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    The item receiving power... the switch, the lights, the motor... whatever.
    The purpose of the fuse is to prevent the wiring from overheating and burning the vehicle.
    As long as the switches are operating relays, you can do this safely.

    I'd stick with a 5a fuse and 18ga wire for the switches and to the relay from the switches. 10a fuse and 12ga wire will be adequate for a pair of 55w lamps, and if you get a 30a relay, the wire is large enough to move to a 20a fuse if you later decide to upgrade to 100w lamps.

    Make the run from the battery to the "main" fuses as short as possible. I showed them close to the lights for simplicity, but in practice, you want as little wire between the power source and fuse as possible.
    Also don't connect both fuses to a common 12ga wire and then run that to the battery... again, that is for simplicity. Each fuse holder needs to go directly to the power source.

    DUALLIGHTS.JPG
     
  11. comajoe

    comajoe [OP] Well-Known Member

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    "I see! said the blind man when he picked his hammer and saw."
    a pic is a1000 words, i got it. thank you!
     
  12. Rich91710

    Rich91710 Well-Known Member

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    The example switches are lighted. If you are using non-lighted switches, then leave out the ground coming from the top terminal.
     
  13. Rich91710

    Rich91710 Well-Known Member

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    Now... A little creativity...

    The project: Install fog lights and driving lights.

    The problem: No dash space available for more switches... or... in my case... too cheap to pay another $75 for a 2nd switch.

    The goal: One switch, two sets of lights, both lights operating legally (fog lights only operate with low beams, shut off with high beams, driving lights operate only with high beams and automatically shut off when dropping back to low beams).

    The solution:

    DUALLIGHTS2.JPG


    The secondary relay is wired to the high beam coil so it is not energized any time the headlights are on... might make it last a bit longer.

    Of course, the 2nd relay must be a 5-pin relay with pin 87a installed.

    So the parking light provides power to the aux light switch. Closing the switch closes the 1st relay, which sends power to the 2nd relay.
    The 2nd relay is switched by the high beams. When not energized, it directs the power from the 1st relay to the fogs. When it is energized, it directs power from the 1st relay to the driving lights and kills the fogs.
     
  14. Mts49

    Mts49 Well-Known Member

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    Very good info Rich, I'm about to mount some lights and this will be very helpful!
     
  15. Mts49

    Mts49 Well-Known Member

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    Just to recap,
    A 30A relay can handle 2 100W lamps using 12GA wire and a 20A fuse close to the battery.

    Correct?

    And the green wire that triggers the relay from the switch does not have to be bigger, since it isn't carrying any load.
     
  16. Rich91710

    Rich91710 Well-Known Member

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    Correct. 200w is "only" 15a (but don't run 400w on one 30a relay, remember the 80% rule), and 12ga is good for a 20a fuse.
    The NEC actually used to allow 14ga to carry 20, but about 20 years ago that was changed... it is still "rated" for 20, but with the condition that a 15a fuse is used :confused:

    For the relay coil, you don't need much. Wire size is more for mechanical strength, and I won't use anything smaller than 18ga in a car or motorcycle. A 5a fuse would be more than enough and will protect the 18ga quite well.
     
  17. TacoBran

    TacoBran Your Unique, Just Like Everyone Else

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    Rich,

    Now what if you wanted to run 4 or even 6 lights on one switch? How would you acomplish this? The switch isn't carrying the load, the relay is correct?

    So you could put as many lights as the relay could handle correct?

    Edit- found my answer in your post a few up.
    You CAN connect more than one relay to the switch, if for example, you want to operate 4 100w lights from a single switch.

    Now my question is, what would be the cleanest way to wire this up?
     
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