Measuring Headlight Voltage Drop

[keytouch]

So whilst investigating making my headlights brighter, I did some measurements of the voltage drop for my headlights.

My only problem was not knowing whether the measurement is meant to be with the lights actually plugged in providing a load, or not.

These are my results-

Battery -engine off - 12.93v
Battery -engine on - 14.38v

Dipped headlight - with light load - 9.91v
Dipped headlight - no light load - 13.89v

Full beam headlight - with light load - 10v
Full beam headlight - no light load - 13.82v

Sidelights - engine off - 12.55v
Sidelights - engine on - 13.70v
Sidelights - dipped on - 12.60v
Sidelights - full beam on - 12.60v

Any help interpreting these and which figures I should be comparing would be greatly appreciated.

[California Dreamin]

Here is mine: (relays & new wiring)
Starter battery voltage across the terminals (No Engine)......12.7 volts.
Across terminals engine running no load.........................14.51 volts
Across terminals engine running FULL BEAM ON 20 amp load.14.41 volts
Now: directly at the H4 bulbs still with all 4 lights on..........13.52 volts

Mines a 0.89 Voltage drop (all guns blazing ) 4 light model

Your 9.91 volt measurement on dip beam has an incredible 4.47 Voltage drop ...3.29 volts lower than the bulb needs to attain 100% illumination. This means that your bulbs are probably working at less than 30% !!! shocking.

European car manufacturers work on a headlamp voltage of 13.2 volts giving 100% bulb illumination output. Daniel Sterns article says: take that down to 11.22 Volts (85% of nominal voltage) and all you get is a paltry 53 percent of normal the rated light output!

Copied from Daniel Sterns Relay article: These figures show a 9006 low beam bulb rated at 12.8 volts 1000 lumens..not the same as our H4's but is a good example of how voltage drop seriously effects light output as a percentage.

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


Your lights are crying out for relays and new wiring mate..

Martin

[ghost123uk]

All such measurements need to be done with the "load" (bulbs in your case) plugged in and working.

Martin is correct (of course ) those results are very poor. If you fit the relay upgrade, especially my preferred version, that is the one that takes it's main feed to the relay(s) from a heavy auxiliary wire you fit that goes right to the battery +v, (rather than the one that takes it's feed from the fuse box) you will notice a HUGE improvement. Then, and only then, consider fitting some "Nightbreaker" bulbs. They are very good but need that relay mod to get the required voltage. Full details in our wiki

[ELVIS]

Mine are off fusebox chap.

What was your measured voltage difference difference between straight from battery and just from fusebox?

[CovKid]

I did the same as Ghost although I ran a very thick cable to an isolated post under the dash from the battery. Can't say I measured the difference - didn't seem much point as as its as good as you can get. The original cable to fusebox isn't up to much.

[ELVIS]

Cheers chap.

Anyone got quantifiable results to go with Jon and Martins?

Might test my P terminals and see what I am getting

[ghost123uk]

Aye, as yours are running off the dash end of the cable, you are in a good position to measure voltage under there, lights on full, and compare it to the voltage at the battery. Would be good to know. No massaging the figures though

Mind you, the cable that goes from the drivers seat to up front will vary from van to van in it's condition, as per when CovKid had all that "black wire corrosion" in his wires. Some will be better than others. Thinking about it, I bet the V drop from dash to battery is even more an issue on a Diesel van with the battery at the back.

[California Dreamin]

Cheers chap.

Anyone got quantifiable results to go with Jon and Martins?

Might test my P terminals and see what I am getting

I probably need to add that my relays are fed with two separate 35amp cables straight from the starter battery. Each cable independently feeding either dip or full beam circuits (redundancy) so if something does go wrong only one circuit is effected. There are also separate earth posts both sides, behind the lights.
If 13.2 volts is indeed equal to 100% light intensity then its no wonder my lights are so bright lol.
What I would be interested in knowing is the difference in voltage at the bulb between a relayed system using the old wiring to the bulbs and a design that renews the wiring all the way.

[CovKid]

[ELVIS]

Will measure my P terminals on Monday Martin

[AdrianC]

It's also worth measuring between the live terminal for the light and a good solid earth - that'll tell you whether your problem is the earth to the bulb, the feed, or a bit of both.

[California Dreamin]

I created two earth posts (one each side) to give the lamps the best possible chassis return..




Martin

[keytouch]

So I have finally finished the relay upgrade.
Ran wires straight from the battery to the front. Relays in a nice water resistant case, wires crimped and soldered, new earth posts fitted.

A quick voltage check was showing 13.2 volts with the engine running and lights on.
So an increase of 3 volts and that's with the van not having been run for a few weeks so the battery was probably charging up. I forgot to measure the voltage at the battery.

[AdrianC]

So I have finally finished the relay upgrade.
Ran wires straight from the battery to the front. Relays in a nice water resistant case, wires crimped and soldered

You've fused those feeds from battery to relays, yes?

[keytouch]

Hell yes. about 3 inches from the battery
Diesel engine so the battery is as far away as you can get, 4 square mm tinned thinwall wire rated at 39 amps, one one for each dipped and full beam. 30amp maxi blade fuse on each wire