interesting site discussing voltage drops in headlight circuits

[Gerald F. Chase #17714]

   I happened to find a very informative website with electrical-engineering discussion on headlight circuits, wiring, and voltage drops:   http://www.danielsternlighting.com/tech/relays.   
I have no financial interest in this firm:  I am publicizing it for its educational value.

   I've noted some limited skepticism on a "Brand X" American heavyweight club site as
regards stock wiring, such as original-sized battery cables.   I'm somewhat knowledgeable but not an electrical engineer so as to be able to confirm or refute.

   I confess that I'm a bit surprised that relays may NOT be installed on all headlight
circuits by the manufacturer.   After all, they're used on horn circuits, right?

   I believe that it is at least fair to concede that American automobile manufacturers
have, in the past, installed marginal equipment in certain areas . . . like shock abosorbers.   Thus, I do NOT think it's reasonable to NECESSARILY CONCLUDE that any and all "upgrades" to OEM is not necessary or beneficial:  I don't "buy" that
argument.   

   Therefore, I encourage self-education on this interesting subject.   Comments?


       Jerry Chase

[Jerry Chase @17714]

Recently, I read a claim by a contributor to a "Brand X" heavyweight website BB that
some automobiles made in the 1940s and 1950s did indeed come from the factory
with RELAYS in the headlight circuits.   I cannot confirm or deny.   Can anyone here?

I certainly understand the advantage of relays in the six-volt cars.   Is it a case whereby
the automotive engineers, a bit after the 12-volt era, collectively decided that relays
"were no longer necessary"?

Related to this question is the question of whether owners of old Cadillacs routinely
select thicker-than-stock battery cables when replacement time comes.   Some say
that merely new cables reduce the voltage drops sufficiently.   Others say that
a larger cross-sectional area naturally eases the flow of electrons.   I tend to agree
with the latter, figuring that the "edge" in performance by thicker cables are well worth the addtional cost over OEM stock gauge. 

Agree or disagree?

[Mike Josephic CLC #3877]

I agree with you.  Thickness = more ability to handle higher loads = more electrons
able to flow.

It's the same reason that in stereo equipment it has been known for years
that a thicker (heaver gauge) speaker cable gives better results.  Especially if,
for example, your pushing high wattage over 20-30 feet.

Mike

[Misfit]

I fully agree. I replaced both of the stock battery cables, with "00' welding cable. Both the battery connection and the starter/ground connections were soldered, then soldered and crimped into the connectors. The difference in the way the starter works is dramatic. Instead of droning to do it's job, it spins like a gear reduction drive unit.

The same with the example of the speaker wiring. I ran 10 gauge speaker wire for a distance of near 75 feet from the head unit out to the pool/patio area. The sound quality difference is amazing. The volume control barely has to be moved to entertain the neighbors. Though I'm not really sure they can/could appreciate Classical music.   

Fins

[J. Gomez]

Jerry,

If you are referring to the electrical article in general, I would say I do agree with it up to a certain point. There are several other variable he left out or failed to add details.

He suggests using a thicker gauge wire for the headlight; in this case there are several variables one needs to take in consideration.

What is the length from the power source up to the connection, what is an acceptable voltage drop, what is the maximum current load for that device, etc, etc?

The engineer will take this data and formulate the appropriate wire size, fuse, etc, if the amperage exceeds the margin for the circuit a device would need to be place closer to the load i.e. a relay.

In the case of these older cars the footswitch switched the positive side to the low or high beams. So it was considered as the intermediate device with the positive wire having a different gauge (16g or 18g) than the ones for the headlamps (20g or 18g).

So back in those days a drop of 0.7V up to the headlamps could well was within the acceptable margin.

The horns are big load sources 10A to 15A so a relay is a must in this case.

Just a simple example for the high beams;
Headlight re-wiring from switch to last headlight = 10’, lamp is (2) 6014 low (4A @ 50W)/high (4.7A @ 60W) beam seal lamp with a 12V supply â€" two headlamps = 8A low 9.14A high

18g-12V-10’-10A load (safety margin) = voltage drop 1.3V
16g-12V-10’-10A load (safety margin) = voltage drop 0.8V
14g-12V-10’-10A load (safety margin) = voltage drop 0.5V 
12g-12V-10’-10A load (safety margin) = voltage drop 0.3V   

Same circuit with a relay closer to the source;
18g-12V-8’-0.5A load for relay = voltage drop 0.05V
16g-12V-8’-0.5A load for relay = voltage drop 0.03V

Relay to head lamps;
18g-12V-2’-10A load (safety margin) = voltage drop 0.26V
16g-12V-2’-10A load (safety margin) = voltage drop 0.16V

You can manipulate these numbers around depending on the distance to and from, but the bottom line is  placing a relay somewhere is the circuit eliminates the need to go with thicker gauge wiring to accomplished the minimum voltage drop to the source.

We all know the automobile industry had experimented with several notions of eliminating as much wiring as possible by moving control circuits closer to the source, electronic controls to multiplex several functions via a single copper path, and even using fiber optics instead of the bulky wire harness. Well guess what the 2011 models still have wires all around the chassis and body.

As for your last topic the battery cable, the ticker the wire is the less resistance and thus a large amp load it can carry, when you crank that 6V starter you would need all the amps the battery can supply up to it.

[P Cedergren]

Apart from a 1960 Cadillac I also have a 1967 New Yorker (which is my daily driver, except in winter).
The New Yorker had the worst low beams of any car I have ever owned.
I bought Daniel Stern's Cibies and wired in relays, and now it has the best low beams of any car I have ever owned. What a difference!

I don't know if the main improvement was the improved headlights or the reduced voltage drop, but I think it's worth doing both at the same time.

/Per C. 4218

[Philippe M. Ruel]

About battery cables : their size is important only to the starter (which features a relay - on fender apron on FoMoCos, built-in on most other cars). And the most voltage-dropping device in the starter circuit is not cables but connections : a wire brush, copper grease and a good 1/2" spanner firmly held will do a lot, before changing wires.

About other circuits : in the 6-volt era, headlights dimness upon switching on turning lights was a common and well-accepted fact.

On my own car, the headlight circuit features a 6-V  "Marchal"-brand relay, which I assume was installed by the dealer before car was delivered to its owner : two other, identical relays are used in the horn circuit and in the second, vintage accessory, three-tone horn circuit. By the way, "Marchal" headlights replaced factory sealed beams (very uncommon in Europe and illegal in some countries) as well.

Another advantage of a relay in headlight circuit is that it protects headlight switch from burning, especially when using modern, high-power (and high-amperage) bulbs.

And when I completely restored the Hydro-Lectric circuit on my car, I ordered all wires in original cotton-braided colors, but one gauge thicker than original.
I will do the same when restoring the main harness, because engineers have always faced technical and financial requirements, and we are talking about technique only (engineers are neither optimistic nor pessimistic : optimists think the glass is half full, pessimists it's half empty, engineers it's twice too big).