Headlight harness relay upgrade... with DRLs?

[Tex06]

3 hours ago, gogmorgo said:

 

I’m also not excited about a hold-in voltage below 5V, given on the off chance the head lights are switched off with high beams on, then the DRL voltage might be enough to keep the relay latched so you’ll just have high beams on full up until you either shut the truck off or turn the low beams back on... Correct?

 

 

Shouldn't be an issue. That's just the voltage that it will absolutely unlatch, no matter what over an entire factory run of these things (probably several 10s of thousands at a time).  It's most likely much higher than that, probably just below the "latch in" voltage (IIRC they're usually about .5-1VDC difference in real world application). Worst case, add in a small resistor just before the relay. It'll drop the voltage the relay "sees" effectively raising the unlatch voltage. Bonus, it would also raise the latch-in voltage closer to 12VDC.

[derf]

Would this be a workable design to block the 5v to the relay but let the 12v through?

 

https://electronics.stackexchange.com/questions/160460/shut-off-circuit-when-under-a-certain-voltage

[gogmorgo]

1 hour ago, Tex06 said:

Shouldn't be an issue. That's just the voltage that it will absolutely unlatch, no matter what over an entire factory run of these things (probably several 10s of thousands at a time).  It's most likely much higher than that, probably just below the "latch in" voltage (IIRC they're usually about .5-1VDC difference in real world application). Worst case, add in a small resistor just before the relay. It'll drop the voltage the relay "sees" effectively raising the unlatch voltage. Bonus, it would also raise the latch-in voltage closer to 12VDC.

The resistor really is starting to seem like the easiest and simplest answer. It’s effectively what I was trying to accomplish with the zener. Or at least what I was ending up accomplishing.

 

But now we’re back into me not being 100% on how to properly spec electronic components, so I’m going to run this by you to see if it seems correct. I’m probably overthinking things a lot.
 

A typical automotive relay can be expected to draw somewhere between 100 and 200 mA, usually closer to the former. Measuring from headlight socket to battery ground with engine running gave me 13.5V drop. A resistor that gives me a 4V drop will put me in the neighbour hood of 9.5V, which should be enough to trigger the relays. At 0.1A, that’s a 40Ω resistor. If however the relay is pulling 0.2A, that resistor is going to give me an 8V drop, which is not ideal. So I should be planning for in the middle of that somewhere? Assume 0.15A, spec a 30Ω resistor to give me a drop of between 3 and 6V across the resistor? Most relays I remember measuring current draw on the switch circuit have been in the neighborhood of 0.12A, so I think that would be a fairly safe option.

Am I correct in assuming that the 30Ω resistor will still provide a ~3V drop when presented with a 5V source, or will the relay continue to act as the bigger voltage drop in the circuit, and proportionally decrease the voltage drop across the resistor, so I’d only end up with a ~1.1V drop on DRL mode, so I might want to go back to a bigger resistor after all?

Also when choosing a power rating, am I looking at dissipated heat (calculating with voltage dropped across resistor) or total circuit power, (total system voltage)?

 

1 hour ago, derf said:

Would this be a workable design to block the 5v to the relay but let the 12v through?

 

https://electronics.stackexchange.com/questions/160460/shut-off-circuit-when-under-a-certain-voltage

This definitely would work, but I’m liking the simplicity of the resistor method above. Likely cheaper and less daunting for a beginner to reproduce.

[Ωhm]

1 hour ago, gogmorgo said:

Yes. As soon as you turn on the headlights with the dash switch, the DRL module stops doing it’s thing.

Since the DRLM will stop doing it's thing, can you rewire the High Beam Relay so that pin_30 (COM) will now go to the Harness Headlight Sockets and Pin_87 (NO) has the fused B+ on it. Now take the 5vdc from the DRLM and run that to Pin_87a (NC).

[gogmorgo]

14 minutes ago, Ωhm said:

Since the DRLM will stop doing it's thing, can you rewire the High Beam Relay so that pin_30 (COM) will now go to the Harness Headlight Sockets and Pin_87 (NO) has the fused B+ on it. Now take the 5vdc from the DRLM and run that to Pin_87a (NC).

Are you asking if I can take the 5V signal directly off the DRL module instead of picking it up at the headlight socket? This would work, but one of my goals is to avoid tapping into more of the vehicle harness than just the headlight sockets, which does complicate things a bit.

[Ωhm]

5 minutes ago, gogmorgo said:

Are you asking if I can take the 5V signal directly off the DRL module instead of picking it up at the headlight socket?

Yes. Make Pin_30 common to both Pin_87 (12vdc) and Pin_87a (5vdc).

[gogmorgo]

20 hours ago, Ωhm said:

Yes. Make Pin_30 common to both Pin_87 (12vdc) and Pin_87a (5vdc).

I’m not entirely certain if this is what you were getting at, but I’ve revised my diagram again based on it. It does simplify the circuit by entirely removing the DRL relay, which is nice.

I’m going to build this latest without the resistor on the high beam switching circuit intially, just to see what happens. The parts store in town carries Bosch relays, and when looking up a data sheet, I see an operating range of 8-16V, so in theory they won’t switch with DRL. In theory...

[Ωhm]

Let the Truck Headlight Socket control the HB relay coil (Pin_86) only. Using the DRLM (5vdc) output, wire that directly to Pin_87a only.

[gogmorgo]

17 minutes ago, Ωhm said:

Let the Truck Headlight Socket control the HB relay coil (Pin_86) only. Using the DRLM (5vdc) output, wire that directly to Pin_87a only.

Again, not an option I want to explore. It would work just fine, but I don’t want to tap into any part of the harness other than the truck socket and battery, same as the “normal” relay harness.

[omega_rugal]

without messing with the wiring? you must make your own module... not easy, not worth it...

[Ωhm]

 

Make something like this and you can rewire any relay without touching the vehicle harness.

[gogmorgo]

8 hours ago, omega_rugal said:

without messing with the wiring? you must make your own module... not easy, not worth it...

This is literally what we’ve been discussing the whole time, trying to avoid switching a relay with 5V. It can definitely be done.

 

7 hours ago, Ωhm said:

 

Make something like this and you can rewire any relay without touching the vehicle harness.

Considering I’m building a relay harness, yeah, that’s part of it. None of the relays I’ve had in my diagrams up to this point have been part of the truck harness.

[Ωhm]

9 hours ago, gogmorgo said:

None of the relays I’ve had in my diagrams up to this point have been part of the truck harness.

What I'm trying to say is, remove the HB relay and rewire the HB relay block using the spade connectors. Should make for no harm done.

[omega_rugal]

9 hours ago, gogmorgo said:

It can definitely be done.

 

without electronics like diodes,transistors and eve ICs, i don't know how...

[gogmorgo]

4 hours ago, Ωhm said:

What I'm trying to say is, remove the HB relay and rewire the HB relay block using the spade connectors. Should make for no harm done.

Strictly referring to the relays within the “upgrade” harness. Yes. I’d be more inclined to install and repin a weatherpack, but that’s just me. 

I should maybe add that I’m not just trying to manage the one MJ with the hacked apart harness. The first one I want to do is completely stock with no relay harness in it, so I’ll be building that harness first to be a simple plug-and-play setup. The other truck has unfortunately been sitting unregistered in the back of the yard at work for the last couples years without a ton of progress being made on getting it back on the road, and I don’t anticipate that changing much until I get some of the other projects I've got that I can actually legally drive out of the way first.

 

4 hours ago, omega_rugal said:

 

without electronics like diodes,transistors and eve ICs, i don't know how...

 

I’m reasonably confident what I’ve got should work. As a bit of an experiment on the drive to work this morning I shut the headlights off with the high beams on, and there was a split second interval between the lights shutting off and coming back on as DRL. I’m thinking that should cure any sort of hold-in problem I might encounter, meaning it would really just be down to adding a resistor to the switching circuit on the off chance that 5V would be enough to make it buzz or something, which at this point I kinda doubt.

[gogmorgo]

Been thinking about this again lately. I bought all the stuff to build the harness last fall/winter, but it's just been sitting in a shopping bag in the corner. Don't really know what happened there but I sorta lost interest... ADHD things I guess. 

At any rate, I just went out and tested the latching and unlatching voltage of a handful of relays I have sitting around, including the ones I bought, using the dash light dimmer from a headlight switch I have laying around to reduce voltage. They all switched at around 5.5-6V according to my very cheap analog multimeter. I'm not confident in the accuracy of the reading, but judging by the MJ's voltmeter the multimeter reads low, so even though it's borderline I don't anticipate the relays will switch with the DRL voltage. More of a concern is that they don't unlatch until the power is cut completely, which may be a bit problematic if the headlights are switched off with the high beams on. So hopefully the brief delay I see when doing that is actually an interruption in power and not just filaments warming up, because I don't know that I'll be able to find a resistor that knocks 5V down to <1V without also knocking 12V down below 6V.

So I'm thinking I'll just go ahead and build the harness like I was planning, see what happens... if I ever get around to it. Lots going on right now, unfortunately.

[Silverfox]

I realize that this might be a little late but I thought I would add something for anyone who might come across this post.

If you cut your relay open you will find a thin band clamp that holds the relay pins. When the relay is energized it will draw the ins to the closed position. I was having the same problem with the drl and the 5.5 volts that kept closing the circuit when it wasn't supposed to.

I heated up that copper or bronze strap and I put a little solder on the edge just giving it a little more resistance.  I was using a 9v dc power supply to test it to make sure I haden't added to much which I had to remove some at one point. This may not be the scientific method you were hoping to figure out but I'm pretty sure it will do the Jobe just fine for you! Good luck!

Silverfox

[gogmorgo]

LMAO no I haven’t actually gotten further with this. ADHD things I guess. Hyperfocus on some idea for weeks and then encounter some tiny hiccup and stuff everything in closet to get buried until suddenly I need to accomplish something ¯\_(ツ)_/¯

 

I haven’t gone back through the thread to see if I said this already, but I had been leaning towards a small resistor to knock a few volts off. But the issue I encountered there was that going through spec sheets on automotive relays, there was some pretty wild variation. Most didn’t list a “hold-in” voltage, but some were so low that it was clear something was needed. But some of the relays listed trigger voltages that were high enough to mean I couldn’t knock too many volts off the top or I couldn’t guarantee I’d get enough voltage to trigger every relay out there. And that’s where I got stuck. 
Doctoring the relay accomplishes basically the same as adding in a resistor, but it also doesn’t accomplish the goal of wanting off-the-shelf parts that will be guaranteed to work first time every time.  
The other solution that would work is a variable resistor, allowing the user to dial it down if it won’t trigger, dial it up if it holds in, for whatever their system is, but that’s messy. And given some relays would hold at basically no voltage means there would be trouble triggering the relays at all.

 

I’m still convinced there’s got to be a simple solution from off-the-shelf components, but I’m just not knowledgeable enough about electronics to properly know where to even start figuring that out.