Voltage Drop

[Hokiefyd]

I measured the voltage drop on the CR-V today as instructed on Daniel Stern's website. That is, with the headlamps on, measure voltage between low beam terminal on the bulb (HB2 bulb) and the positive battery cable. That gives the voltage drop on the positive side. Then measure voltage between the the ground terminal on the bulb and the negative battery cable. That gives the voltage drop on the negative side. Add together for total system drop.

On the positive side I have a 0.6V drop and on the negative side I have a 0.2V drop, for a 0.8V drop in total. This was at about 12.1V reference (across both battery terminals) with the lamps on (engine off obviously).

This appears to represent a 6.6% voltage drop. But Mr. Stern goes on to say that lamp output decreases at the power of 3.4 as voltage drops, so it's not linear. So at 95% of reference voltage (which is about what it seems I have), lamp output is 83% of its rated output.

Have any of you measured your voltage drop before and after installation of a harness? I'm trying to justify (or not) the cost/effort of installing a harness.

Thanks!

 

[brianl703]

Don't you need to know what the rated voltage of the lamps are and the operating voltage (engine running) of your vehicle's electrical system in order to come to any conclusions about how much of the lamp's rated output you aren't getting?

If your vehicles electrical system operates at 14V, which is typical, and you're getting 1V of drop, the lamp is operating at 13V, which may be within specs. (Seems that most lamps are rated at 12.8V).

 

[sciphi]

The Cruze was 12 volts with the engine off, and 14 volts with the engine on. It still benefited much from the harness I built for it. Our Fit also showed identical voltage to battery voltage and engine voltage, respectively.

I suspect the real story might be in the amps the OEM wires can carry, and the watts the bulbs are producing as a result. The factory wires may well be maxed out on amperage of factory wires to limit wattage for better bulb life as part of that whole "no-maintenance" sthick. An 18-gauge wire is rated for 2.3 amps for power transmission. A 14-gauge wire commonly used in upgrade wiring harnesses is rated 5.9 amps in the same application. It's a "fatter pipe", so more amps can safely be carried.

Another issue might be in grounding. That power needs to go somewhere, and having a grounding point back through 10 feet of 18-gauge wiring isn't helping put as much current as possible through the headlight filament. On my Cruze's harness, my ground wires (also of 14-gauge wire like the rest of the harness) are at most 14" long. Likely that's a much better current path than the OEM grounds far away from the headlights.

So voltage, while nice, might not be the only reason why OEM headlights do not perform as well as some of us would like.

 

[Hokiefyd]

Originally Posted By: brianl703
Don't you need to know what the rated voltage of the lamps are and the operating voltage (engine running) of your vehicle's electrical system in order to come to any conclusions about how much of the lamp's rated output you aren't getting?


All bulbs are rated for output at 12.8V reference and rated for life expectancy at 14.0V reference. Neither rating, however, is pertinent here because I'm looking for how much voltage I'm losing with my factory wiring, to determine whether or not I feel it's worth it to build a wiring harness that would supply straight battery power to the bulbs through a relay. The bulbs would both burn brighter and expire sooner this way.

The H4 bulb is nominally 55W on low beam and 60W on high beam. The current required for those wattages, at 14.0V, is 3.9A and 4.3A, respectively. It's likely that if the wiring were larger, I'd experience a smaller amount of voltage loss.

And this is exactly what I'd like to quantify. If, via a harness, I would still have a 0.5V loss, for example, I wouldn't feel like it'd be worth the trouble. However, if I would have an immeasurable amount of voltage loss by using a 12- or 14-gauge size wire, then I might think it's worth it.

What's the big deal? Well, I have two hesitations about a harness. The first is up-front cost. To do it with quality materials, the cost isn't trivial. Secondly, I'm quite literally trusting my life to an aftermarket relay that I would buy where, should it fail, I lose all forward lighting. That gives me pause, which is why I'd like to be sure the benefits of the harness are worth the risks.

 

[sciphi]

Both our cars have foglights also. So if the harness in my Cruze goes belly-up, there's still enough forward lighting to safely pull over and plug in the OEM headlight connectors.

Also, you still have high beams on a separate circuit. So you'll still have some lights, even if the low beam part fails.

I decided to minimize the risk of failure by getting quality relays, connectors, and crimper. The wire is less important than the connectors. Think of the harness as a rope. It's only as strong as the knots. My "knots" are US-made connectors, name-brand relays (Tyco Electronics), heat-shrinking every connection, and then wire-looming/electrical taping everything using Scotch Super 88 electrical tape and 20 feet of wire loom. Crimping practice was done before trying to assemble everything.

Another note: Get 10-gauge connectors for 14-gauge wire where a split from 1 wire into 2 is needed, such as when running wire to each bulb. Double up a single 14-gauge wire by folding it back, or use 10-gauge wire to feed each connector when needing to run 2 separate wires. I doubled up 14-gauge wire, and have had no issues running stock-wattage bulbs.

In all, it was about $100 for all the supplies and tools needed. Not trivial, but worth it IMO.

 

[Hokiefyd]

Good point about the high beams being workable in a pinch. You are right, they are on a separate circuit.

 

[Seguino]

I run two 100W driving lights with 14ga wire and have almost no voltage drop, so you should have no trouble with two 60W headlights and a good harness.

If you are concerned with the failure of an aftermarket relay and want a fail safe system, just run separate relays to each light. Not much chance of both relays croaking at the same time.

 

[brianl703]

Originally Posted By: Hokiefyd
If, via a harness, I would still have a 0.5V loss, for example, I wouldn't feel like it'd be worth the trouble. However, if I would have an immeasurable amount of voltage loss by using a 12- or 14-gauge size wire, then I might think it's worth it.


This can be calculated, if you know how many feet of 12 or 14 gauge wire you will use in your harness, so you know how much resistance your harness has, and can use ohm's law to calculate the voltage drop through that resistance for a given amperage.

Quote:
Secondly, I'm quite literally trusting my life to an aftermarket relay that I would buy where, should it fail, I lose all forward lighting.


Use a quality relay, such as Tyco (now TE Connectivity), Bosch, Potter & Brumfield, Aromat, Omron, or anything sold by Mouser Electronics or Digi-Key. Neither of those companies sell cheap junk. Most auto manufacturers who use relays in their headlight circuits seem to use the typical 30 AMP ISO relay. I don't think I'd use anything rated less.

Usually, though, relays fail in one of two ways: They stick on or they stick off. I have never seen a relay fail in a manner where the contacts opened up while the coil still had power (which is the failure mode that you are concerned about). I have seen them fail to open the contacts when the coil power is turned off (stick on) or fail to close the contacts when the power is turned on (stick off).

In either of these cases, giving the relay a good tap usually fixes the problem, at least temporarily.

In my experience, sticking on is far more common than sticking off.

 

[MolaKule]

Okay, just got to ask.

How many Lumens (light) output difference is there between 0.5 and 1.5 volts drop in your system?

I.E., are you really going to notice a difference?

 

[brianl703]

I have only ever used a headlight harness as a fix for a factory wiring error that caused the headlight circuit to be overloaded when the fog lights were turned on. There is a TSB for the problem and it was less effort and expense, compared to fixing it the TSB way, to just use a headlight harness. I have never otherwise bothered with one.

In the car that I installed the headlight harness in, the only noticeable effect is that I could run the foglights or high beams without tripping the thermal breaker in the headlight switch. There did not appear to be any difference in the brightness of the headlights. That harness was assembled with 14-gauge wiring.

 

[Seguino]

Originally Posted By: MolaKule


How many Lumens (light) output difference is there between 0.5 and 1.5 volts drop in your system?



Thanks to Daniel Stern for providing the following chart on his website

10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens Rated life voltage
14.5V : 1528 lumens

As you can see, 1V makes quite a difference in light output

 

[jaj]

Originally Posted By: MolaKule
Okay, just got to ask.

How many Lumens (light) output difference is there between 0.5 and 1.5 volts drop in your system?

I.E., are you really going to notice a difference?


Light output varies as the 3.4th power of the voltage ratio, so 14V vs 13V is a 29% difference in luminoscity. Your eye, however, is also non-linear, so it will visualize it as a 16% difference.

 

[Vikas]

But our eyes need four times the lumens for us to perceive doubling of the brightness. So 25% improvement would only be noticeable if you do side by side comparison.

 

[VWguy]

Originally Posted By: MolaKule
Okay, just got to ask.

How many Lumens (light) output difference is there between 0.5 and 1.5 volts drop in your system?

I.E., are you really going to notice a difference?


For what's its worth, I know there is a huge difference. My daily driver vw bug had dim lights. Swapped in a pair of sealed beam halogens and no improvement. Installed my Neolite H-4's and still poor light projection onto the road. Performed a voltage drop and had a 2.5v drop from battery to headlights. Installed supplemental wiring and dual relays and now have a .5v drop. Light projection is fantastic for a 35 year old car. Reflective range is approx 1000 feet and 3 lanes of width. Recently installed the Xtra Vision std wattage H-4's and now my lighting is better than some newer cars.
Hope this helps, Bill.

 

[widman]

When I build my Corvair, right from the start I knew I wanted good lighting, so I built it with Halogens and relays.

Only problem is that then my wife was not satisfied with the lighting on the BMW, so I put Halogens in it a couple of weeks ago.

 

[Mud]

I use an aftermarket headlight relay harness on both of my CV's, but I upgraded the relays to auto reset circuit breakers. No issue over several years. As I remember, I measured several volts higher at the headlight sockets after the harness install, but more important to me was that the headlight load no longer ran thru the headlight switch contacts. With the harness, the switch simply is used to send current to energize the relays.

On my 02 CV, I installed a true E55 projector retrofit as I don't believe in using cheap ebay "conversion" kits that blind everybody.

Even on the regular halogen lights on the 03 CV there was a noticeable difference in brightness.

For the harnesses in both of the CV's, they actually use 3 circuit breakers/relays. One each for left/right lo beam and one for both left/right hi beam. This allows each lo beam side to operate independently.

Here's the wiring diagram, ignore the CCFL circuit, I mulled over installing halos but decided against it. This wiring diagram would apply to halogen lights as well, but would not of course use the ballasts. Since these are combined hi/lo beams a diode is needed to avoid the lights cutting off when hi beams are selected.

General pics from a write-up I did on cvnet, the E55's use the hi/lo beam shutter that is shaped to provide the proper cutoff.

 

[Hokiefyd]

Thanks guys. I think I'm going to buy a harness from headlightservices.com. I saw a good reference to them on the Candle Power forums.

http://headlightservices.com/Wiring.html

73 bucks gets me a complete turn-key harness, with diode relays and soldered connections. Even a nice male H4 connector for the trigger mechanism. Alternatively, I could spend 42 dollars and get all the materials. I could probably buy the materials for that, but it'd be close, and I'd spend enough of my own time and gas that I think it's worth it to just buy the kit from these guys.

 

[BubbaFL]

Originally Posted By: Hokiefyd
I'm quite literally trusting my life to an aftermarket relay that I would buy where, should it fail, I lose all forward lighting.


You could wire up two relays in parallel for redundancy, if that is a major concern.

You could even wire up the second relay to a separate switch hidden somewhere under your dash - that way if the regular headlight circuit fried itself you'd still have headlights (but not taillights or markers)

 

[eljefino]

Originally Posted By: BubbaFL
Originally Posted By: Hokiefyd
I'm quite literally trusting my life to an aftermarket relay that I would buy where, should it fail, I lose all forward lighting.


You could wire up two relays in parallel for redundancy, if that is a major concern.


One relay and fuse per bulb would work well. Forget wiring parallel, let each bulb live its own life independent of the rest of the car. (Or is this what you are saying?)

If one doesn't use high beams much, they could leave one high beam wired up "stock". The first impulse if one lost their low beams IMO would be to go for the "flash to pass" feature. With the lead only feeding one bulb, the voltage drop on the stock harness would be less, anyway.

 

[HerrStig]

I found a quick low beam improvement by taking ONE low beam off the circuit so the factory wiring only had to feed one bulb. The other bulb was powered by a relay triggered by the low beam voltage from the stock harness but fed through a fused line right to the battery. Not as good as a full harness but an improvement and essily returned to stock. I cut the load in half on about 80% of the headlight harness. THis was in
mportant because the low beams were fed THROUGH the dash switch, reducing current flow through that circuit helped a lot.