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High beam and low beam, lit together in H4 bulb. It's possible?

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  • #16
    Originally posted by xnfot View Post
    Regarding this on H4 headlight car, when the high beam turns on, and the low beam turns off, which part is the one that commands the low beam to turn off? The relay? Or is it the BCM?
    The relay just provides power to the channel that should be powered. The controller decides which one to get powered (via the relay).
    Jul 2012 ROTM (3-way quad headlight) ; Sep 2015 ROTM (custom muli-lens 7" fogs)

    3-way quad wiring; foreground limiter; squirrel finder;

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    • #17
      Originally posted by xnfot View Post
      Regarding this on H4 headlight car, when the high beam turns on, and the low beam turns off, which part is the one that commands the low beam to turn off? The relay? Or is it the BCM?
      Relay(s) supply power to the headlights, which is controlled by either the stalk/switch or BCM depending on the vehicle.

      For example I have a BCM-controlled (they call it MICU) Honda with independent relays for low and high beam; the light switch/stalk does not directly control the relays, instead depending on the what MICU input receives a ground signal from the stalk it'll energize one of those relays.

      My 2002 4Runner on the other hand has its relays directly controlled by the stalk.
      Originally posted by HK45
      I don't even look to see what Eddie writes anymore. I'm too busy staring at his avatar.

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      • #18
        H4 bulb has 3 pins. The car's harness could use a Common Positive or a Common Ground. Basically what happens is that the headlight switch either via a relay or via BCM or on its own swaps which pins on the bulb are powered. How the swapping happens isn't particularly important to understand how the bulb works.

        Common Ground, then there are 2 Positives and the switch swaps which is used (one positive is low beam and the other positive is high beam).

        Common Positive, then there are 2 Grounds and the switch swaps which is used (one ground is low beam and the other ground is high beam).

        It's the same bulb either way. Halogen bulbs don't care which pin gets Positive or Ground as long as there is a complete circuit. Other dual-filament bulbs work the same way.

        To keep the low beam on with the high beam, you'll need to put a diode between the low beam and high beam wires. The direction of the diode depends on whether the car's harness is wired for Common Ground or Common Positive. However, as others noted above, this would end up generating a lot more heat which could damage the bulb or housing.
        www.fadingarrow.com

        2001 Black Firebird Formula 5.7L V8 --- 75th Anniversary Package
        Headlights: Sinolyn 3" D2H Projectors with 35 watt HID

        2013 Blue Mustang GT 5.0 V8 Premium
        Headlights: Stock D3S Bi-Xenon

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        • #19
          I was able to energize my add-on harness by tapping into my '02 4Runner's (H4) headlight circuit before the OEM relay connection, no diodes needed.

          It's super easy on common-positive H4 systems. Connect your relay harness' trigger + to the common + then the trigger - to a good ground.

          Again this is a horrible idea to do if someone's trying to power both H4 halogen filaments at the same time, this is for someone trying to connect add-on relay harnesses for HIDs to their OEM headlight wiring.
          Last edited by Eddie; May 28th, 2020, 10:27 AM.
          Originally posted by HK45
          I don't even look to see what Eddie writes anymore. I'm too busy staring at his avatar.

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          • #20
            This can be accomplished using a diode but as others have stated it isn’t recommended. Since you have an h4 housing why not do a retrofit? Very easy to do with mounting shafts. Self aligns as well.

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            • #21
              Originally posted by Eddie View Post
              Again this is a horrible idea to do if someone's trying to power both H4 halogen filaments at the same time, this is for someone trying to connect add-on relay harnesses to their OEM headlight wiring.
              Unless you want to see some explosions/fires

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              • #22
                Originally posted by carlthetruckguy View Post
                This can be accomplished using a diode but as others have stated it isn’t recommended. Since you have an h4 housing why not do a retrofit? Very easy to do with mounting shafts. Self aligns as well.
                I would do this retrofit because I'm considering to install aftermarket headlights (angel eyes type), which have 2 bulbs (H1 bulbs). So by that, I want it for when I drive at rural roads (alone, with no other cars present) that have no street lighting

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                • #23
                  Originally posted by niZmO_Man View Post

                  Unless you want to see some explosions/fires
                  Definitely not! But like I stated above, I want the 2 beams to light simultaneousely because I'm considering aftermarket headlights that have 2 bulbs in them
                  Last edited by xnfot; May 27th, 2020, 09:23 PM.

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                  • #24
                    Originally posted by xnfot View Post
                    Definitely not! But like I stated above, I want the 2 beams to light simultaneousely because I'm considering aftermarket headlights that have 2 bulbs in them
                    If you are doing an aftermarket housing and want both to turn on then the previously stated diode method will work perfectly fine.

                    Just make sure you have the wire tap with the diode going the right way.

                    Should be Highbeam>Diode>Lowbeam

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                    • #25
                      Originally posted by satrya View Post

                      The relay just provides power to the channel that should be powered. The controller decides which one to get powered (via the relay).
                      I see... So, in this case, can I program the controller to not turn off the low beam when I turn the high beam on?

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                      • #26
                        Originally posted by carlthetruckguy View Post
                        If you are doing an aftermarket housing and want both to turn on then the previously stated diode method will work perfectly fine.

                        Just make sure you have the wire tap with the diode going the right way.

                        Should be Highbeam>Diode>Lowbeam
                        Ok then. In the case I make "light call" to someone, in that case only the high beam will turn on once I have the diode? I will be going with this solution then. As long as it is safe, then all good
                        Last edited by xnfot; May 29th, 2020, 01:53 PM.

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                        • #27
                          Originally posted by xnfot View Post
                          I see... So, in this case, can I program the controller to not turn off the low beam when I turn the high beam on?
                          With the right relay harness, the ballast will always get power whether the original OE wiring powers the low beam filament or high beam filament of an OE-compatible halogen bulb. In high beam mode, the relay harness also passes some current to the solenoid to move the shield.
                          Jul 2012 ROTM (3-way quad headlight) ; Sep 2015 ROTM (custom muli-lens 7" fogs)

                          3-way quad wiring; foreground limiter; squirrel finder;

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                          • #28
                            Originally posted by satrya View Post

                            With the right relay harness, the ballast will always get power whether the original OE wiring powers the low beam filament or high beam filament of an OE-compatible halogen bulb. In high beam mode, the relay harness also passes some current to the solenoid to move the shield.
                            Regarding the harness, I currently have one that was included with my aftermarket Xenon H4 kit for my factory H4 headlights, and it's connected to the battery. The way it works is this:

                            When I make a light call/flash-to-pass, a magnetic mechanism moves the bulb back and the bulb turns until the stalk goes back to its position, and when my lights are on and I pull the stalk to activate the high beams, the magnetic mechanism pulls the bulb back, and it stays back until I deactivate the high beam from the stalk, and the light still stays on. What I mean to say is that the low beam never turns off as it would normally do with my stock halogen lights. In the case of my aftermarket headlights (they take H1 bulbs) that I'm considering, I will replace my H4 Xenon bulbs with H1 Xenon bulbs for those. My kit is compatible with them.
                            Last edited by xnfot; June 1st, 2020, 10:02 AM.

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                            • #29
                              Originally posted by xnfot View Post
                              Regarding the harness, I currently have one that came with my aftermarket Xenon H4 kit for my factory H4 headlights, and it's connected to the battery. The way it works is this: When I make a light call/flash-to-pass, a magnetic mechanism moves the bulb back and the bulb turns until the stalk goes back to its position, and when my lights are on and pull the stalk to activate the high beam, the magnetic mechanism pulls the bulb back and it stays back until I deactivate the high beam, and the light still stays on. What I mean to say is that the low beam never turns off as it would do with my stock halogen lights. In the case of my aftermarket headlights (they take H1 bulbs) that I'm considering, I will replace my H4 Xenon bulbs with H1 Xenon bulbs for those. My kit is compatible with them.
                              Sounds like you already have what you need.

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                              • #30
                                Originally posted by carlthetruckguy View Post

                                Sounds like you already have what you need.
                                In that case, it seems that half of my work is done with this. The other half must be done by putting a diode because the way it's like this, and by adding the new H1 bulb aftermarket headlights, everytime I will make a light call/flash-to-pass, both my low beams and high beams will turn on simultaneously, and the latter is something I want to avoid by putting the diode
                                Last edited by xnfot; June 1st, 2020, 12:43 PM.

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