Headlight Relays Redux

[ZOA NOM]

Another benefit of the six relay setup is that I can use my hi-beams and my Hella 450 driving lights simultaneously. Even with stock bulbs, they throw an incredible amount of light.

[ianc]

Ron, that is exceptionally clean looking! Nice work! ZOANAS, how about some pics of your install?

ianc

[ZOA NOM]

Just zip ties for now. I'll be dressing it up after driving with it for a little bit to be sure there aren't any bugs.

[coloradoporsche]

Hi Zonas,

I commend your ingenuity, and I would like to add to a couple of comments…..

…there is theoretically no voltage drop across a closed set of contacts.

There is always a "contact resistance" across closed contacts. I'd say 50mOhms might be typical of a power realy with 100mOhms being on the high end and probably the manufacturer spec. From a practical standpoint (as opposed to theoretical) the load is small.

If a relay fails, it will most likely fail closed in the low beam (normally closed) configuration

This depends on the circuit design.
On a "single side stable" relay the armature will tend to spring to the non-energized position if the coil fails for some reason, but the contacts can fail either on the NO or NC side depending on what kind of load you are carrying. The contacts can weld to the NO side just as easily as the NC side.

Unless you wired your lights in series, your relay will be carrying twice the current mine will. Who's is more likely to fail?

Technically, this is a true statement. But…if your circuit is designed properly, the relay will not fail prematurely. Meaning 2 relays that will carry 5A are no more reliable than one relay that is designed to carry 10A.

Here is a typical relay life chart…..



(I don’t know what relays you are using, so this is just meant as an example of typical performance of a relay). Life in number of operations is inversely proportional to load.

But a well-designed circuit should last close to the mechanical life of the relay which is typically 1,000,000 operations or more. How many times are you going to turn on the headlights? If you only got 300K operations, that would be about 800 years assuming once per day.

So, you are right in that for a given relay, lower load is better. But a beefier relay (“beefy” is an Electrical Engineering term ) will handle the job just as well. What I mean is, 3 heavy-duty, automotive relays like this one could work just as well as 6 smaller relays, be just as reliable, and you’d use less parts.



To be clear: I’m not trying to knock your design. It looks great. (To be honest, I’m running my H4s off of the headlight switch for the time being )

I just post this to provide discussion of other design options.

Best Regards,
Martin

[ZOA NOM]

Is there a way to operate my driving lights, high beams and low beams independently with 2 relays? I can't see a way to turn on my driving lights when I hit the flasher or the high beams or the fog switch with only two relays. The load carrying benefit is just a bonus. The SPDT relays were inexpensive and readily available from JC Whitney, and rated at 30 amps each. With four 100 watt forward facing filaments on simultaneously, I will only draw 8 amps through each relay. The two-relay setup will draw 16 amps through each, and you would not be able to turn off the driving lights (assuming they were simply wired in parallel). Your chart ends at 14 amps for a typical relay.

[HarryD]

I ended up ordering the kit from Daniel Stern. Besides the relays and bases it included new bases for my headlamps, some fuses and misc hardware.

While I only did my headlamps, my overall plan may also include Fogs and Driving lamps. It will be wired like this:

[ZOA NOM]

Same as mine with an extra set of fogs. Looks good. Initially, I was looking for DPDT relays, but found the SPDT relays more common and available.

[ianc]

coloradoporsche,

I liked your post: great info.

I agree with zoanas that the standard Porsche relay will probably fail in the open position. On my design, that would equate to an inop, since I don't use 87a.

I see a potential benefit in zoanas' use of both 87 and 87a, since either position will result in juice to the beam, but it seems to be negated by the two relays pictured before it though (upper left). If either of these fail open, there will be no juice to that beam!

I also agree with colorado's point that a properly-sized relay will be reliable for a particular application. I've read that the Porsche standard relay will easily handle 30A. Just to be sure, I have a 30A circuit breaker in the main battery feed, but it has never tripped...

I'm a computer guy, so I tend to worry about mulitple points of failure. Dunno what to say about the fog light piece of it. I never really use them...

ianc

Edited to say: zoanas, I think you should print out your diagram in reduced size on some sort of durable sticky paper and affix it near the circuit on the tub itself. If made of a suitably durable material, it will give a quick reference to any future owner. I printed labels on our label maker at work to put in the relay panel cover for explanatory purposes.

[ZOA NOM]

If either of these fail open, there will be no juice to that beam!

True, but they are necessary when using both 87/87a on the output, or the lights would never turn off. If I get in a bind, I can always pull the relay and jumper across it until I get home.

I just went for a drive to check the candlepower, and WOW, I don't think I'll need bigger bulbs. The stock highs with the Hella 450's turn night into day.

[ZOA NOM]

If made of a suitably durable material, it will give a quick reference to any future owner.

Future owner? Are you kidding? I've only put 90k on this thing. I'm just getting warmed up.

[HarryD]

Originally posted by ZOANAS
Same as mine with an extra set of fogs. Looks good. Initially, I was looking for DPDT relays, but found the SPDT relays more common and available.

Daniel sent me the DPST relays with two #87 pins. I think it makes for a cleaner install. But as most of us know, two ways to most things.... my way and "the other way". Often both will do the job.

I should note that, under the stock wiring scheme, there are times when both the high and low beams are energized simultaneously such as when I flash my high beams when only the low beams are on. Because I have not rewired anything until after the stock switches, I maintain the stock switching strategy. Your wiring plan eliminates this. I should note I am speaking for the wiring plan for my '73. Later cars may be different.

good thread!

[ZOA NOM]

I should note that, under the stock wiring scheme, there are times when both the high and low beams are energized simultaneously such as when I flash my high beams when only the low beams are on.

That's correct, my flasher results in my high beams along with the Hella 450 driving lights lighting up the night. God help anyone I flash!

[HarryD]

Originally posted by ZOANAS
That's correct, my flasher results in my high beams along with the Hella 450 driving lights lighting up the night. God help anyone I flash!

Ah!! Didn't catch that detail.

[jpahemi]

Has anyone wired the fogs to run independantly without the low beams on?
j.p.

[Quicksilver]

Originally posted by ZOANAS
Is there a way to operate my driving lights, high beams and low beams independently with 2 relays? I can't see a way to turn on my driving lights when I hit the flasher or the high beams or the fog switch with only two relays. The load carrying benefit is just a bonus. The SPDT relays were inexpensive and readily available from JC Whitney, and rated at 30 amps each. With four 100 watt forward facing filaments on simultaneously, I will only draw 8 amps through each relay. The two-relay setup will draw 16 amps through each, and you would not be able to turn off the driving lights (assuming they were simply wired in parallel). Your chart ends at 14 amps for a typical relay.

You can run a wire with a diode in it from the high beam circuit to the energizing connection on the Foglight relay.

You do have a basic function problem with the foglight/highbeam connection. The jumper between the 2 circuits will make it so the foglights come on with the high beams. The problem is that when you turn on the foglights it will turn on the high beams.

BTW - You don't want to run both the low and high beams together for very long. It will seriously shorten the bulb life.

Here is a pic of my relay panel...

I tried to make it shaped (and mount) as much like the factory fuse panel as possible.

The mess at the bottom is the circuit breakers that I used instead of fuses.

[imcarthur]

How have you guys incorporated the 'city lights' on H4s into these circuits?

I was thinking of them as daytime running lights (or please don't hit me lights).

Ian

[Mysterytrain]

I installed the city lights when I went with the Cibie headlights they are tied to the parking light circuit. I also did the Daniel Stern mod where the turn signal is tied to the side marker..so I get a little more visablity. Third brake light is next.

[ZOA NOM]

You do have a basic function problem with the foglight/highbeam connection. The jumper between the 2 circuits will make it so the foglights come on with the high beams. The problem is that when you turn on the foglights it will turn on the high beams.

BTW - You don't want to run both the low and high beams together for very long. It will seriously shorten the bulb life.

First, I don't have fog lights. They are Hella 450 driving lights, so I want them to come on with the high beams. Second, my setup prevents simultaneous high and low beam, and the headlights and driving lights are on independent circuits, so bulb life will not be affected.

[ZOA NOM]

Originally posted by jpahemi
Has anyone wired the fogs to run independantly without the low beams on?
j.p.

My setup allows this. Since I had to leave the fuse for the old fog relay in place to keep my alarm from not shutting off when I reattached the battery, my fogs (driving lights) will operate with only the running lights on, or with the low beams on. They also flash with the flasher (with or without any other lights on), and come on with high beams.

[HarryD]

Originally posted by jpahemi
Has anyone wired the fogs to run independantly without the low beams on?
j.p.

Check my diagram above.