Far-reaching driving light

[e30davie]

I'm pretty sure that old Toyota Corolla's cost half of what these cars did... The ~100 amp alternators should not show any signs of voltage drop.

I just measured mine, m20b23 with later model headlights.

at idle with the headlights on (not high beam) the battery showed 13.05v, at the headlight was 12.55v.

0.5v is significant enough i reckon if you want maximum light. certainly not as much as my old corolla, i was down in the 11V range.

[berlow94]

I would think that voltage drop is just strain on the alternator at idle. Keep the motor revved at 2k rpm and I bet there is less than 0.1 volts being lost between the alternator and the headlights.
Even my crazy light bar doesn't pull enough amps for the copper 18 ga. wire to drop voltage.
Keep in mind that a wire needs to get pretty damn hot before it starts building any sort of resistance.


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[Mo Brighta]

Headlight circuit voltage drop

Most voltage loss between a source and consumer is at the terminals, not along the wires. Voltage losses along 100 feet of an unbroken length of adequate gauge is measured in tenths and hundredths of a volt. Losses from a terminal loose from thermal cycling, plus 30 years of exposure and the resulting corrosion (such as headlight connectors) may be closer to a volt.

And knowing the output versus voltage characteristics of filament lamps, little losses mean big reduction in brightness.

One of the neat tools I found at my wire supplier is a 'terminal extractor' set that allows me to remove and either replace or tighten terminals within a headlight or any other connector. Clean male terminals, tighten females, and use contact grease (Permatex 67VR) - all good ways to reduce or eliminate voltage drop cheaply.

If you don't have a terminal extractor, a tiny jeweler's screwdriver will do most of the time. You need good eyes and an understanding of how connectors go together, but it's a fairly basic process once mastered.

Happy Motoring!

[berlow94]

Most voltage loss between a source and consumer is at the terminals, not along the wires. Voltage losses along 100 feet of an unbroken length of adequate gauge is measured in tenths and hundredths of a volt. Losses from a terminal loose from thermal cycling, plus 30 years of exposure and the resulting corrosion (such as headlight connectors) may be closer to a volt.

And knowing the output versus voltage characteristics of filament lamps, little losses mean big reduction in brightness.

One of the neat tools I found at my wire supplier is a 'terminal extractor' set that allows me to remove and either replace or tighten terminals within a headlight or any other connector. Clean male terminals, tighten females, and use contact grease (Permatex 67VR) - all good ways to reduce or eliminate voltage drop cheaply.

If you don't have a terminal extractor, a tiny jeweler's screwdriver will do most of the time. You need good eyes and an understanding of how connectors go together, but it's a fairly basic process once mastered.

Happy Motoring!

Great info!

How much would you say that this <1 volt drop affects non-filament bulbs such as LED or HID headlights?

[Das Delfin]

^ interested in the answer here

[Mo Brighta]

Apples and oranges, here is why.

LED and HID light sources use a regulated voltage, far less primitive than filament heating to make light. Filament lamps glow because current passes through a resistor (the filament) which gets hot and glows. No circuitry involved, just the resistance of the filament.

LED and HID light sources have an intervening device. LED are controlled by regulated current at a lower than input voltage, sometimes internally so you don't see the device. HID are controlled by voltage and current in an obvious control box, at far higher than input voltage.

My best answer - neither one will suffer lower output with a slightly reduced input voltage. The voltage and/or current regulation are designed to produce the electrical output required to make nominal light output a virtual certainty.

Both LED and HID draw less current than filament lamps anyway, so they stress the wiring and connectors less and, as a result, may experience a lower loss in terms of percentage drop in the voltage at the control circuitry, which is NOT the voltage to the lamp.

That's the way I understand it, anyway. Your cell phone chargers do a similar task, and that's why many of them do not need a voltage converter - just an outlet adapter. Look at the input specs on any modern AC adapter; it likely says something like "INPUT 100~240VAC 50~60 Hz."

[Das Delfin]

^ That's the same idea I had. The LED or HID ballast does the job of supplying the correct voltage and current for the bulb. Thanks!