DIY Sequential Taillights for approx $20

[Highlifeman]

Originally Posted by sjmautoprod

At 5 ohms, you need more than 35 watts. This one is 50... MP850-5.00-F-ND

This one is a bit less money... RT50J-5.0-ND.

That is a very good point, I forgot to recalculate the power requirement. A 50 W resistor is probably a good idea anyway to give it plenty of headroom.

[brettsimons]

Originally Posted by whitedemon

I dont think the relay will help. I did a current draw on one blinker bulb with the car not running ( so around 12.5v) and each bulb draws 2.5 amps. So 5 amps total when blinkers running, if you are drawing 6 amps with the resistors that shouldnt set the bcm code therefore changing relays will not help. The bcm is setting a code because it doesnt see enough current and thinks the bulb is out. Probably just need a little bigger load resistor to draw a tad more. I have had personal stuff come up this week and havnt had time to mess with it, ill try to get something on the car this weekend and let everyone know.

I was just thinking that the bulbs are in series, correct? So if they are in series with a total of 5 Amps and then I have this delay circuit added in series with a load resistor that because of the relay is always adding another 2 amps, then shouldn't I have to replace the relay and the load resistor so that the load resistor is only drawing power during the time in which the bulb is being delayed and then be switched back off when the bulb is turned on so that the total amperage always 5 instead of 7 like I currently have?

[sjmautoprod]

They are in parallel, but... If you have stock bulbs, that logic stands. You only need the resistor in the circuit when the relay is off (technically, only when the inner is on and the outer is off).

[brettsimons]

Originally Posted by sjmautoprod

They are in parallel, but... If you have stock bulbs, that logic stands. You only need the resistor in the circuit when the relay is off (technically, only when the inner is on and the outer is off).

Ok so if the bulbs are in parallel with the second bulb having the load resistor of 5 ohms on top of it's 5 ohms of resistance that it already creates, then I believe the BCM is being caused due to the total resistance being 3.33 amps instead of the expected 2.5...

What it's expecting: 1/x=1/5+1/5 x=2.5

What it would be getting with the current relay: 1/x=1/5+1/10 x=3.33
^ The 10 is from the 5 ohm resistor and 5 ohm bulb.

So if we replace the relay with one with the NC terminal like sjm suggested, then the resistance would be a total of 5 ohms from the time the circuit receives power, to the time the load resistor gets switched out of the circuit and the bulb comes on keeping a constant 5 ohms of resistance instead of the current relay that keeps the load resistor always in series with the bulb creating a 10 ohm resistance...

[sjmautoprod]

Based on my experience with the tail-light circuits , I think this should be fine...

[Highlifeman]

Originally Posted by brettsimons

Ok so if the bulbs are in parallel with the second bulb having the load resistor of 5 ohms on top of it's 5 ohms of resistance that it already creates, then I believe the BCM is being caused due to the total resistance being 3.33 amps instead of the expected 2.5...

What it's expecting: 1/x=1/5+1/5 x=2.5

What it would be getting with the current relay: 1/x=1/5+1/10 x=3.33
^ The 10 is from the 5 ohm resistor and 5 ohm bulb.

So if we replace the relay with one with the NC terminal like sjm suggested, then the resistance would be a total of 5 ohms from the time the circuit receives power, to the time the load resistor gets switched out of the circuit and the bulb comes on keeping a constant 5 ohms of resistance instead of the current relay that keeps the load resistor always in series with the bulb creating a 10 ohm resistance...

If you have the resistor in series with the circuit, that is correct for when the light is on, but when it's off there would be no current going through either the resistor or the bulb. Which would make it draw only 2.5 A while only one light is on. It would also make the outside light dimmer when it's on. That's why I'm pretty sure you have the load resistor hooked up in parallel making it draw 5 A with one light on and 7.5 A with both on.

I feel like I'm explaining this really badly...

[Highlifeman]

Originally Posted by sjmautoprod

Based on my experience with the tail-light circuits , I think this should be fine...

That would put R1 in parallel with the tail light when the relay is energized. R1 should be connected to the NC terminal and ground.

Edit: Never mind, the image is now correct.

[sjmautoprod]

Damn. That's right. Image updated.

[brettsimons]

Originally Posted by Highlifeman

If you have the resistor in series with the circuit, that is correct for when the light is on, but when it's off there would be no current going through either the resistor or the bulb. Which would make it draw only 2.5 A while only one light is on. It would also make the outside light dimmer when it's on. That's why I'm pretty sure you have the load resistor hooked up in parallel making it draw 5 A with one light on and 7.5 A with both on.

I feel like I'm explaining this really badly...

Then that makes two of us who are really bad at explaining!

As for what I was talking about, I was just thinking of hooking up the resistor so that, for instance, if you hit the brake, the resistor is only active from the time the bulb SHOULD be on to the time the timer runs out and the bulb actually comes on. Basically, for that split second when the bulb is off because of the timer, the resistor mimics the bulb until the bulb actually comes on so that the BCM sees the normal amperage.

[dragom]

ok could someone list what is needed for this circuit and the diagram

[brettsimons]

Originally Posted by dragom

ok could someone list what is needed for this circuit and the diagram

Well we haven't officially changed anything from the last post of parts except for the resistor has been changed to 5 ohms:

Originally Posted by sjmautoprod

At 5 ohms, you need more than 35 watts. This one is 50... MP850-5.00-F-ND

This one is a bit less money... RT50J-5.0-ND.

Edit: But I would hold off until we get everything working with no BCMs unless your fine with the error or want to test with me!

[Highlifeman]

Originally Posted by brettsimons

Then that makes two of us who are really bad at explaining!

As for what I was talking about, I was just thinking of hooking up the resistor so that, for instance, if you hit the brake, the resistor is only active from the time the bulb SHOULD be on to the time the timer runs out and the bulb actually comes on. Basically, for that split second when the bulb is off because of the timer, the resistor mimics the bulb until the bulb actually comes on so that the BCM sees the normal amperage.

That is what should happen with the resistor connected to the NC terminal on the relay or with it connected to the drain of the first MOSFET in the dual MOSFET design.

[brettsimons]

Originally Posted by Highlifeman

That is what should happen with the resistor connected to the NC terminal on the relay or with it connected to the drain of the first MOSFET in the dual MOSFET design.

OK good were on the same page then! Haha so I'll see if I can get the new relay with the NC terminal and 5 ohm resistor today and test it tomorrow. Cross our fingers this works!

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[brettsimons]

So I called around and couldn't find a relay with an NC terminal for the resistors and a NO terminal for the bulb so in the spirit of DIY, me and my brother opened up the relay and soldered the wire to the resistors to the part of the relay where the NC terminal would usually come from. Since I know that's a horrible explanation, I posted some pictures! It may be hard to see but there is a black wire coming from the top of metal contact that the armature normally rests upon (NC) and leads out through the front of the casing where we drilled a home for the wire.

But basically for this design, you just take the original design, but you place a load resistor from the NC terminal of the relay (which you can make yourself ) directly to the ground. I've driven with it for a little bit now and so far so good but I would really like to get a good days worth of driving in before I can definitively say it works.

Oh and I haven't had time to get a new resistor yet so I'm still using the 5.9 ohm resistor I made from an 8, 50, and 44 ohm resistor in parallel. The 44 ohm is made from two 22 ohm resistors in series. But even with this it still seems to be working fine. Again I would still like to get some more driving time in with it before I give a definitive answer!

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