Need Some Advice on Using Relays (Preventing Counter-EMFs)

[Disaster]

Turn signals designed for a particular filament bulb have reflectors that are designed to work with that filament's size and placement. LED "bulbs" just have a bunch of LEDs plastered on them and light is beamed out willy-nilly (or worse, just a single emitter pointed in one direction).

Maybe willy...but never nilly... ;-)
I agree but I can't think of any reason you couldn't get the proper illumination by designing an LED array to yield enough light for the purpose of lighting up a reflector. It might not be the most efficient design, but it seems doable.

Turn signals, side marker lamps, license plate lamps, reverse lamps, and brake lamps, just like headlights, have certain photometric requirements that must be met. They can't be met unless they are using the bulb they were designed around.

What photometric requirement do you think an LED array might not be able to meet, behind a position/turn signal marker?

I could be abysmally wrong with this statement, but it would seem that the bulb is chosen first, and then the fixture is designed.

That sounds right...but obviously not how retrofitting or aftermarket stuff works.

 

[-Virgil-]

I agree but I can't think of any reason you couldn't get the proper illumination by designing an LED array

I thought we were talking about "LED bulbs", those clusters of LED emitters based so as to fit in place of a filament bulb. Those don't work, period. Certainly it's possible to design and build an LED array to serve whatever function is desired (front turn, rear turn, parking lamp, tail lamp, brake light, backup light, etc.) but it's nowhere near as simple as a lot of people seem to assume. See this thread; the issues raised in it apply to all roadgoing LED lamps, not just headlamps.

to yield enough light for the purpose of lighting up a reflector. It might not be the most efficient design, but it seems doable.

Ah, now you're talking about "LED bulbs" again. No. It simply, flatly does not work, period, and it wouldn't work even if you had a magic spell to cast that would make the thermal issues go away.

How big an issue is it with a reflector/marker style light that just needs to light up? Shouldn't a 180 degree bath of light...or two or three...or an array of LEDs, light the reflector up so that it visibly works?...ie...can be seen well by others.

No-no-no-no. That's not how it works at all. EACH AND EVERY automotive lighting function must meet very specific performance requirements throughout a range of specified test points. See here and here for starters. Your "just needs to light up" and "can be seen well by others" ideas are not even a little bit close to how these devices are specified and regulated, and are not even slightly appropriate standards for homemade lighting mods. Remember, these are safety devices we are talking about. They are not toys. They need to work the way they need to work, otherwise your car becomes a danger to yourself and everyone else on the road -- whether you realize that or not. There are also liability issues to keep in mind. If you're involved in a crash and it's discovered that you modified your car's lighting system in such a way as to take it out of compliance with the applicable regulations, you could very easily find yourself in a very expensive world of hurt...no matter how adequate you think your homemade lights ought to be considered.

 

[mrb]

What do you mean "at a push" and why do you feel LED's are only good for interior use?

Those cheap pre-made modules/arrays of LEDs designed to fit the form-factor of a filament bulb are generally unsuitable for external automotive applications for the reasons already highlighted.

I mean "at a push" using them for automotive interior use as the modules will often have very concentrated areas of heat that is not well controlled and could deform or damage the light fitting in the long-term. There are scores of stories/threads of molten license plate bulb holders floating about from poor LED modules.
I actually tried out some white LED 501/W5W side-light modules, they got scorchingly hot and were shifting heavily to the blue after just a few minutes indicating the LEDs was not happy, no way would they have lasted the claimed 50K hours.
I'm certainly not saying LEDs aren't suitable for exterior use at all, just the entire light fitting needs to be designed and built around the characteristics/needs of the LEDs used.

 

[Kuryakin]

Let me elaborate (which I should have done in the first place), DRLs that run the headlights at reduced power aren't really compatible with relay setups, at least not easily. I suppose you could add an extra relay to switch the DRL function in and out, but there's some issues that need to be addressed, not the least of which is the reduced voltage will still pull in your typical headlight relay.

Now, if you're using the turn signals for DRLs, that's eliminates the DRL discussion from headlight relays!

Just so you guys know how it works...

There are 2 relays. The first relay switches the high beams to a series at this intersection: (ACC/ON) AND (Out-Of-Park). It does this by switching the ground of one bulb to a +. The bulbs are in parallel stock, so it becomes a series with this one change.

The second relay breaks the first one (by switching it's coil) when the passing lights OR low beams are on. For this, I will tap into the combination switch output lines in the steering column.

So the whole gate is:

(ACC/ON) AND (out-of-park) AND NOT(Passing-Lights OR Low-Beams)



What do you mean by this? Are you saying the module won't work?

 

[-Virgil-]

Let me elaborate (which I should have done in the first place), DRLs that run the headlights at reduced power aren't really compatible with relay setups, at least not easily.

Yup, it can be done, but most ways of doing it are not very elegant -- relay count gets too high. Unless you want a big honkin' power resistor or a PWM box in the circuit, you set up your DRL mode to put the low and high beam filament in each headlamp in series with each other (obviously not an option with Xenon low beams). The result is usually a reasonably good DRL. There have been some GM and Nissan vehicles over the years with this kind of "high + low in series" DRL circuitry. But again, the problem with retrofitting it is relay proliferation; you have to have cutout relays to prevent shorts to ground when switching among operation modes.

That said, if you have access to a good (skillful/talented) rebuilder of alternators, the matter gets a good bit simpler. See this patent. There's some Brit terminology to get straight if you want to get hold of the idea being presented. "Dipped beam" = low beam, "main beam" = high beam, "side lights" = parking lamps, and for "dim dip" info, see Wikipedia and Stern's got info here. The basic concept: you pull power off two out of the alternator's three phases. This gives you 67% of nominal voltage, or about 9.6 volts. Depending on the specific headlamps in question, that would be too high for a high beam DRL. Suppose you have a fairly average 50,000 candela high beam at 12.8v; at 9.6v it would give 18,500cd. But it'd work for a low beam or fog lamp DRL, and avoid the bulb blackening that you get when running some halogen bulbs at the low voltages required for high beam DRL operation. Alternatively, a much less bulky, smaller resistor could be used to knock the 9.6v down to 6.4v for high beam DRL operation.

Circuitry wouldn't be too complex. You can get the idea from the patent; a SPDT ("changeover") relay could be used to switch the headlamp feed circuit from the full voltage supply to the reduced voltage supply. There'd be some additional control wiring required, and I haven't plotted it all out as a diagram, but I don't think it would be too hard.

But after all that, it's still simpler and cheaper and less problematic to just throw a turn signal DRL module on it and move on to the next project.

 

[Kuryakin]

And I, for one, am no fan of DRLs in the first place! Therefore, finding the plug under the dash of our Subarus (Subari?) is something I did the first day I got these cars. Only real pain in the $#%& is there's enough voltage STILL in the high beam circuit (even though these have low beam DRLs) to hold the relays in. A 50 ohm power resistor solved the issue. But that's just me...

>>But after all that, it's still simpler and cheaper and less problematic to just throw a turn signal DRL module on it and move on to the next project.[/QUOTE]

 

[hayze]

Hey, thanks for all the detailed advice from everyone.

Anyway, I'm actually planning on doing the fog light modification first (not DRL). It only involves one additional relay. We'll look into the DRLs later.

This is not a DRL modification at all. It just lets me run the fog lights without the low beams.

The fog lights have to shut off with the high beams to be legal. This and the low beam restriction are handled by the control block in the diagram (stock). Basically, the ground from the switch is like a 'request' sent to the control block which then decides (based on the other headlights' operating conditions) whether or not to ground the relay coil. So jumping the control block results in the fogs working with the switch anytime.

The blue is the added circuitry:

By jumping the control block, I remove the low restrictions (good), but I also remove the high beam restriction too (not good). So my idea is to only jump the control block during the condition when the high beams are not allowed to work anyway (low beams off). When the low beams are off, the control block is bypassed, and I don't have to worry about the high beams (because they won't turn on anyway). When the low beams turn on, the bypass is broken, and the fog light operation reverts back to stock which allows the fogs 1) to work and 2) still be under the control of the high beams.

Let me know what you think about the electrical safety of this design.

 

[hayze]

So, can you guys comment on this modification in terms of using the diode in parallel with the relay (the SPDT relay, not the OEM fog light relay- that one has an internal resistor)? If I implement this modification, will it be safe in terms of the counter-EMF?

Also, I was wondering specifically what components would be damaged by the CEFM? I don't know where the CEMF current would run without the diode present. Can you elaborate on this too?

Thanks guys

And Schiemwerfermann, thanks much for all your advice and info. I looked into turn signal DRLs too. I like the idea, but the relay count on the module I came up with would be way too high on my car. The circuit breaker inputs are mixed up (+ and ground) so the OR-gate would require more relays. The total is 5 relays on the module I came up with whereas the high beam DRL module I can implement only requires 2. Also, my turn signal bulbs only have two wires coming out whereas the bulbs in the diagram for the module you suggested have 3. Lastly, sorry for the mix-up on talking about a fog light modification after talking about DRLs, but the general concept of preventing CEMFs applies to both.

Again, thanks everyone for the info. I appreciate it.

 

[-Virgil-]

I looked into turn signal DRLs too. I like the idea, but the relay count on the module I came up with would be way too high

Huh? Just put in a turn signal DRL module. Zero relays required.

Also, my turn signal bulbs only have two wires coming out whereas the bulbs in the diagram for the module you suggested have 3

That's irrelevant.

 

[hayze]

^^Okay, so I can still use it even though my bulbs have two instead of three pins. Good.

One thing I'm worried about though is my side mirror blinkers. Since they're LEDs that weren't designed for running constantly, then I'm worried that maybe running them as DRL could burn them out prematurely. They might not have heat sinks or something else required for LEDs to run. I wouldn't know much about this except for Honda did not have to consider constant running when designing them. Would this be a problem? Also, can I wire up the module such that only the front incand blinkers inside the headlight assemblies (and not the side mirror blinkers) run as DRL? The front, side, and rear are all in parallel from their output on the turn signal/hazard light relay (each side separately of course).

Thanks a lot,

 

[-Virgil-]

Okay, so I can still use it even though my bulbs have two instead of three pins.

The third pin/wire is for the parking lamp function -- not relevant to DRL operation of the front turn signals.

One thing I'm worried about though is my side mirror blinkers. Since they're LEDs that weren't designed for running constantly

They wouldn't care if you were to run them constantly, but...why would you? Only the FRONT turn signals are operated as DRLs. Not the side blinkers, not the rear turn signals, not the dashboard turn signal indicators...just the front turn signals.

 

[hayze]

Scheinwerfermann,

I emailed the turn signal DRL people. I might grab the module.

Anyway, if you know a lot about that module, maybe you could answer a few questions:

I'm just wondering how they are able to build the module without knowing the specific circuitry of my car. How do I know it will work for sure?

Also, what breaks the circuit? I'll want them to shut off when the parklights/headlights turn on. Is the blue wire for that?

Lastly, if I switch the yellow ignition wire (with a relay), will that act as my own DRL circuit breaker? For ex, if I change my fog lights to work without requiring the headlights, then I'd want to have the turn DRLs shut off with them as well as whatever they originally turn off with.

thanks

 

[-Virgil-]

I'm just wondering how they are able to build the module without knowing the specific circuitry of my car.

They don't need to know what kind of car you drive. It's a pure logic module that monitors the status of the parking lamp circuit, the ignition, the left turn signal, and the right turn signal.

Ignition off: Module is not active, all lamps function as they presently do.

Ignition on, parking lamps on: Module is not active, all lamps function as they presently do.

Ignition on, parking lamps off: Module is active, front turn signals burn steadily as DRLs.

When the driver signals for a left or a right turn, the module sees that and flashes the applicable front turn signal (together with the rear turn signal and, if the car has it, the side turn signal). Depending on how the module is configured, the opposite-side front turn signal stays lit as a DRL or goes dark until the turn signal is switched off.

Lastly, if I switch the yellow ignition wire (with a relay), will that act as my own DRL circuit breaker?

Yes.

if I change my fog lights to work without requiring the headlights

If you do this properly (fog lamps can be used with parking lamps or with parking lamps + low beams, but not with high beams) then no relay in the yellow wire is needed.

I gotta say, you really seem to be making this a good bit more complex and mysterious than it actually is.

 

[hayze]

If you do this properly (fog lamps can be used with parking lamps or with parking lamps + low beams, but not with high beams) then no relay in the yellow wire is needed.

I agree. The new fog light circuit will shut off with the high beams and passing for sure. But are you saying it is illegal to use the fog lamps alone without parklights?

I gotta say, you really seem to be making this a good bit more complex and mysterious than it actually is.

I'm just making sure I know the details of the module as well as how it will coexist with other possible modifications. Actually, I'm being as complex as I feel is necessary when dealing with circuitry and legal stuff. No hard feeling though. I appreciate your replies.

 

[-Virgil-]

it is illegal to use the fog lamps alone without parklights?

Yes.

And very, very unwise to use them alone with parking lamps, in the case of almost all fog lamps on the market, and in any case at speeds above 25 mph.

 

[hayze]

^^what is the reason it is so unsafe? Is there something other drivers can mistake them as?

 

[Alaric Darconville]

^^what is the reason it is so unsafe? Is there something other drivers can mistake them as?

Not so much that as fog lights, by there nature and purpose, are so easily overdriven.

Fudging numbers for illustrative purposes: Imagine driving at 95mph with just your low beams on. That's probably close to what going 40mph with just fog lights (or fog lights and parking lights) on would be like.

 

[hayze]

This fog-alone modification will only be for daytime driving at times when the low beams wouldn't be on anyway. They certainly will not substitute for low beams. The only thing they will do is add noticeability at times when I wouldn't have low beams anyway. And I certainly won't be using only the fogs at night.

So here is my daytime driving plan:

parklight off: turn sig DRL
parklight on: parklights and fogs (if I use the fogs), but no headlights

Plus the halos light up with the parklights too.

 

[hayze]

Okay, now its time for me to get some relays. Do you guys think these ones will work for switching 55W incand headlight bulbs (half-strength as DRL)? I'm assuming it is fine since it is rated at 40A continuous duty and at 12V.

Here is the link:
http://www.texasindustrialelectric.com/relays.asp

Here is the description:
[FONT=Arial, Helvetica, sans-serif]40 Amp Cole Hersee Mini Relay[/FONT][FONT=Arial, Helvetica, sans-serif]
SPDT
Cap Material = Plastic[/FONT][FONT=Arial, Helvetica, sans-serif]
5 Terminals:
# 85 .250
# 86 .250
# 30 .250"
# 87 .250
# 87a .250
12 volts
Continuous Duty
Includes Mtg Bracket
[/FONT][FONT=Arial, Helvetica, sans-serif]Unsealed
Can Be wired to be used for small permanent magnet motors. Electric Door Lock Motors, Small Reversible Permanent Magnet Motor.
Resistor & Diode Models Available.
Order RN for Resistor,
Replacement for Bosch 0 332 204 159
Order RD for Diode Relay[/FONT]

Let me know what you think. If it is not sufficient, then can you suggest another relay off that link?

Thanks.

 

[-Virgil-]

This fog-alone modification will only be for daytime driving

This has already been commented on. Fogs are not legal as DRLs in the USA, and are legal as DRLs in Canada only if so certified (and that provision in Canadian law is being phased out).