100 series headlight voltage drop

[Landpimp]

or lack there of.

I measure the voltage drop from the battery and from the headlight, heres what I got

at battery

at headlight(low beam)

as you can see there is very little drop. Not that adding an upgraded harness would be a bad thing, but IMOP I can't see the need for it if running stock bulbs.

John H

 

[80and100cruisers]

I can make the voltage drop with the best of them When my sub hits...I can't see at night

-Matt

 

[e9999]

hmmm....
if there is no load, as in disconnected connector, wouldn't the voltage be the same regardless of the wire size...? IOW, isn't it the voltage under load that matters?
E

 

[Landpimp]

hmmmm.....maybe? I dunno? but on my other cruisers this is how I checked the voltage before and there was a drop, a good drop(over .5 volt) in most cases.......at least from what I remember



[quote author=e9999 link=board=2;threadid=12382;start=msg113550#msg113550 date=1078199762]
hmmm....
if there is no load, as in disconnected connector, wouldn't the voltage be the same regardless of the wire size...? IOW, isn't it the voltage under load that matters?
E


[/quote]

 

[Rich]

Voltage drop in wiring is due to the resistence of the wire. The amount of voltage drop is proportional to the current flow and the wire resistence. In order to measure the voltage drop you need the wiring to be carrying the current as drawn by the lights. With the headlights on take two measurements. First measure the voltage between the positive and negative battery posts and from this subtract the voltage measured between headlight positive connection and the negative battery post. The result is the voltage drop.

Rich

 

[IdahoDoug]

That's gonna be tough, eh? I'm visualizing using a vice grip to clamp the bulb to something within reach of the harness connector, pushing the connector almost all the way on (to leave room for a probe - hopefully the spade will engage the connector) and having a very hot bulb next to your hand.

DougM

 

[scottm]

This topic continues to amaze me. I just replaced a Hella 80/100 bulb on my Audi, the second in 130,000 miles. Years ago I measured a 2 to 3 volt drop at the headlights as this same controversy swirled on my Audi group. They're so bright I've ordered smaller bulbs this time, my daughter doesn't need big bulbs draining the battery during her short trips around town and at college. So they last a long time and are incredibly bright, what exactly is the problem with voltage drop?

 

[Landpimp]

I will test em again with the light conected............

 

[cary]

[quote author=Scott M. link=board=2;threadid=12382;start=msg113686#msg113686 date=1078228155]
This topic continues to amaze me. I just replaced a Hella 80/100 bulb on my Audi, the second in 130,000 miles. Years ago I measured a 2 to 3 volt drop at the headlights as this same controversy swirled on my Audi group. They're so bright I've ordered smaller bulbs this time, my daughter doesn't need big bulbs draining the battery during her short trips around town and at college. So they last a long time and are incredibly bright, what exactly is the problem with voltage drop?
[/quote]

Voltage drop is important because with a 2 volt drop, light output drops to half of what it would be at full voltage. If you have a 2 volt drop, an upgraded wiring harness would give more output with stock bulbs than the 80/100's with no harness. See the below description.


In many cases, the thin factory wires are inadequate even for the stock headlamp equipment. Headlamp bulb light output is severely compromised with decreased voltage. For example, normal engine-running voltage in a "12-volt" automotive electrical system is around 13.5 volts. At approximately this voltage, halogen headlamp bulbs achieve 100 percent of their design luminous output. When operating voltage drops to 95 percent (12.825v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (12.15v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.475v), bulb output is a paltry 53 percent of normal! [Source: Hella KG Hueck AG, Germany].

 

[scottm]

[quote author=cary link=board=2;threadid=12382;start=msg113778#msg113778 date=1078244253]
Voltage drop is important because with a 2 volt drop, light output drops to half of what it would be at full voltage.[/quote]

I've been hearing those "facts" for probably 20 years. The numbers vary quite a bit, but they're always attributed to a company that sells aftermarket headlight components, usually Hella. I have a catalog with some of their "facts". Would a company mislead you to increase it's profits? Yes, it's not science, it's marketing.

Light, sound, and radio waves don't double in power from a doubling of input power. It takes about ten times the input power to double output. Hella is telling you a two-volt increase at your headlights is ten times the power. You believe this?

I have a '90 quattro with euro lights and four 100 Watt bulbs. I have a voltage drop of two to three volts. A friend in town has a '90 quattro with euro lights and a professionally built and installed headlight harness, and stock bulbs. His bulbs should be brighter according to Hella, but they're much dimmer. The various people I know who've installed headlight harnesses have no visible increase in output. All the harnesses I've seen marketed add complexity and cost, and most reduce electrical redundancy the car was designed with. I've heard of a couple guys losing both low-beams from a relay failure, short, or wiring failure. Stock wiring keeps the two sides separate.

If you're running really big bulbs, you should consider a headlight harness. It should have at least the redundancy of the stock wiring. If you're recommending a product, try to get some facts beyond what the producer provides, otherwise we'll all end up driving Jeeps and buying robot insurance.

 

[Landpimp]

OK, lets try this again........the right way

Voltage measured at the battery

voltage measured at the back of the lowbeam with the headlights on. (if you look close you can see the probe stuck in the back of the connector)

So YES there is a voltage drop of .36 of a volt.

Thanks for correcting me

John H

 

[Photoman]

John,
Pretty neat. Great pics. I take it the motor was running with the alternator kicked in to see these kind of numbers?

Bill

 

[Landpimp]

yep, motor was running.

Great pics.........I dunno about that



[quote author=Photoman link=board=2;threadid=12382;start=msg114085#msg114085 date=1078278613]
John,
Pretty neat. Great pics. I take it the motor was running with the alternator kicked in to see these kind of numbers?

Bill
[/quote]

 

[e9999]

see the difference with before?
E

 

[IdahoDoug]

That's an interesting "mythbuster" comment, Scott. I'll be interested in further comments as I've always gotten strong increases in output and long life from high output bulbs using merely the stock wiring with two exceptions: PIAA bulbs and the recent Hella fiasco. In the case of PIAA, they gave me crap that I was using stock wiring and told me "stock wiring with its voltage drop shortens the life of the filament". I'd heard that before and actually still consider it true simply because of the sheer number of times I've heard it from a wide variety of sources. But since we're questioning such assumptions, I'm interested in why the filament would have its life shortened by not being "at its designed hotter temp"? Generally speaking, larger thermal cycling shortens the life of literally every other component I can think of. So?

DougM

 

[Rich]

Well, here is Sylvania's published design data for automotive bulbs. I believe that they have the science down. 20% voltage drop from design voltage results in a light output reduction of 50%. Likewise a 20% over voltage results in double the light output. Only a moderate increase in power is required to double the light output. Also notable is the major reduction in bulb life if operated above design voltage.

 

[CDN_Cruiser]

I always just look at a flashlight, as the power drops, the buld get dimmer. Correct?

If we take the table above, it would suggest:

100W bulb at 11.5V (2V loss) = 15% loss off of 13.5V = 60% output = 60W actual
55W bulb at 13.0V (0.5V loss with harness) = 4% loss = 90% output = 50W actual

So, your bulbs are running 20% 'brighter' than his are (ignoring stuff like quality of product, etc).

Cheers, Hugh

 

[ryanjl]

[quote author=Scott M. link=board=2;threadid=12382;start=msg114067#msg114067 date=1078277224]
The various people I know who've installed headlight harnesses have no visible increase in output. All the harnesses I've seen marketed add complexity and cost, and most reduce electrical redundancy the car was designed with. I've heard of a couple guys losing both low-beams from a relay failure, short, or wiring failure. Stock wiring keeps the two sides separate.
[/quote]

Hmmmm.... that may be. But everyone on this board who's posted their results after installing the Slee harness, myself included, have seen a noticeable increase in light output while still using the same bulbs. While I may not perscribe to Hella's hype, I find it hard to believe that more power does not equal more light.

 

[cary]

[quote author=Scott M. link=board=2;threadid=12382;start=msg114067#msg114067 date=1078277224]

Light, sound, and radio waves don't double in power from a doubling of input power. It takes about ten times the input power to double output. Hella is telling you a two-volt increase at your headlights is ten times the power. You believe this?

[/quote]

In short yes. You are trying to compare apples to oranges. As you state it takes a 10 fold increase to double audio output, this is because Decibels are a logrithmic function, not linear. Light does not follow this same log curve. Instead, with filimant lights you have to reach a certain wattage (depends on bulb) before there is enough heat being generated for the filimant to have any light output. Once you reach that point, you can increase voltage very slightly and see massive increases in light output at the bulb gets hotter, up until the filimant is overloaded.

Cary