Regarding the voltage drop, keep in that the reference voltage is the voltage supplied by the car’s electrical system not the nominal voltage of the bulb. So if you’re alternator is putting out 14VDC, that’s where you start the calculation.
Maybe the nominal voltage of 12.8 was selected because it accounted for voltage drop. The life limit voltage 14VDC is about the maximum the bulb would ever see. Incandescent lamp life goes down as the voltage goes up.
I had good installation with this kit.
That’s a more significant mod, and as you say, probably better for full power to the headlights.
My goal was only to get the load off of the original switch and prolong its useful life. It is reversible in a few minutes to original removing one nut 4 wires. Shouldn’t be a mystery to any future owner, but I’ve documented it on my worklist that I’ve kept since owning the car. While I say my E lights are white and bright (I think they’re Cibie Halogens), I’m not about to compare them to my wife’s Subaru Outback or my 2006 SL 500.
Go measure it and come back with an answer. You’ll be surprised. Start on the far side of the bonnet at the headlamp on the opposite side from the bonnet plug. Then go from the bonnet plug along the engine loom to where it goes to the bulkhead. Then go into the bulkhead and across the car onto the fuseboard. Now go back via the brown wire back across the car, through the bulkhead back to the engine bay. Then go back along the frame rail all of the way back to the front of the car to the alternator. It’s not going to be a short run, is it?
The only new factor is the shortened (and fresher) wiring, the lack of bullet connectors, centre console switch, old fuses and the addition of a new fuse and relay. The headlamps haven’t been touched.
Power = V squared over R. The “R” at the headlights hasn’t changed, but all of the unproductive R along those connectors, fuse and oxidised wiring is eliminated, so the voltage drop of a high I (as in V=IR) is eliminated. Do the maths of adding 0.4 to 0.5v to the voltage and report back. It’s in the order of 10%
I sell a third brake light for s1 cars which replaces the filament bulb with LEDs and that has prompted me to research this, do the sums and the difference is material.
I found that the typical voltage drop from the front of the car to the back of the car with an old factory harness was in the order of 0.75v. Fitting a brand new replacement harness into a restored car sees that voltage drop clock in at about 0.25v instead.
Getting that “free” 0.5v of extra voltage is productive, because you cannot bump up the alternator voltage past 14.4v without compromising the safety of the battery through overcharging to recover your “lost volts” that way.
kind regards
Marek
All true regarding the voltage drop problems but you’re powering incandescent headlights that have a 12.8V requirement. Dropping .5V from 14V isn’t a big deal. You’re still above the nominal voltage. Using higher wattage lamps requires relays but why not just switch to LED’s? It’s an easier fix.
The current is much lower so the voltage drop is lower. The LED driver doesn’t really care if the voltage is a bit low or high.
LED headlights may not be legal in all jurisdictions. Additionally, to maintain cheap insurance and tax status, type approval may be necessary, so there may be a substantial financial penalty to wanting a non-OEM headlight alternative. LEDs won’t be legal in the UK and countries like Germany and Switzerland fail you on your MOT for this sort of thing.
Dropping 0.5v from 14v is a big deal. You lose (14x14 / 13.5x13.5) -1 of the power - that’s 7.5%. It’s not a case of buying higher wattage bulbs - 7.5% of your available power never arrived to where it was supposed to be used.
kind regards
Marek
None of this wiring is eliminated with a relay. You still have to get from the positive post behind the battery to the the opposite side headlight. The only wiring you actually bypass is from the battery back to the panel. Nor can you count twice for the two headlights. If you save eight feet of wire, it’s more than I would expect. Any improvement here comes from bypassing old connectors and switchgear. Which could just as easily be renewed.
Interesting chaps…. I was always taught 13.2v at the lamp was the correct voltage ….are you saying it can go to 13.5 without it causing a blown sealedbeam
No.
Firstly, the battery is irrelevant, as you are running from the alternator once your engine is running. Granted, I ought not to have counted the wiring in the bonnet as that is common, but your saving is that the path from the alternator all of the way into the centre console and back out again is replaced by a new route which starts at the alternator and only goes forward to where it can easily intercept the original blue/white and blue/red wires - that is the location of the relay. It’s a massive saving of old loom and a bypass of many old bullet connectors, old switches and old fuses.
The old wiring into and out of the cabin is indeed not eliminated - it now carries the coil winding current for the relay and this means it ceases to affect the headlight brightness.
kind regards
Marek
Alternators are commonly set at from 14 to 14.4v for the purposes of charging the battery.
Running a sealed beam at 13.5v instead of 13.2 is putting it at 105% of its nominal rating and I doubt the production tolerance of the unit is even that good, even today.
kind regards
Marek
The below article applies to the U. S. only.
Are LED Headlights Legal? | Policygenius
It looks one would be OK if they use a housing that is designed for U. S. roads, i.e. driving on the right hand side of the road, and keep the luminosity below 3,000.
The electrical system was designed with voltage drop in mind. Are you trying to get it to zero? That’s not possible. .5VDC loss off of 14VDC still gets you 13.5VDC at the headlight. If the nominal voltage is 12.8VDC, I simply don’t see the problem.
Switch to LED’s and forget all the extra relays and fuses.
I think it was actually designed with cost in mind otherwise they would have used relay’s, hardly a new concept in 1961.
Hook up a substantial wire to the block in the bonnet. Run it to the battery or alternator. Like the improvement? You may have a wiring issue. Or just see a difference. Add relays. Not substantial? Leave the electrics in peace and enjoy the car (and give the next guy a chance to do so as well). No need for this ‘debate’.
That being said I like the installation in the first post: easy to reach, not in the way, no new holes, nothing destroyed, clear objective.
For tungsten filament bulbs (including quartz-halide but excluding Xenon and LED) it’s a lot bigger deal than that. That’s because increasing the voltage/wattage results in not just more emission, but a shift in the wavelength. Heat (infrared) is reduced while visible light is increased (the familiar shift from red, through the rainbow, to blue). More power to a given filament shifts the wavelength range towards blue, and in so doing provides more visible light. This phenomenon about doubles the expected increase in useful light from what would be expected from the power increase itself when fitting a relay. IMHO.
Fun fact: Home lamp dimmers for decades created more reddish illumination from dimmed bulbs than from bright ones. But this no longer holds true for LED bulbs–they have the same colour temperature whether bright or dimmed. That’s because their light output is due to a single quantal transition. Added phosphors generate “white” light, but their spectrum doesn’t change with light intensity either.
Hi All, I solved the lighting problem years ago…don`t drive at night…ever.
Regards,
Allen
Double the amount of useful light by raising the voltage from 13.5V to 14V?
It’s a very small change in color temperature.
It’s like tossing chum into piranha-infested waters…
[quote=“MarekH, post:29, topic:429837”]
Firstly, the battery is irrelevant, as you are running from the alternator once your engine is running.
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Power is distributed from the positive stud behind the battery, which is tied with short, heavy cable to both the alternator and the battery positives. Power will be supplied by either or both, depending on temperature, RPM and load conditions. E-Type alternators and generators are marginally adequate, particularly on early cars. Stop for a red light, and the battery is carrying the electrical system. Barring horrendous corrosion, the positive terminals on the alternator, battery, and the distribution stud are always going to be at the prevailing system voltage, within the limits of shop voltmeters.
Sorry to beat a dead horse but it’s light output is up 10%.
The lamp life is down to 70% of it’s normal rating.
The resistance of incandescent lamps is not constant. It changes with temperature.
More from wikipedia
For a supply voltage V near the rated voltage of the lamp:
** Light output is approximately proportional to V 3.4*
** Power consumption is approximately proportional to V 1.6*
** Lifetime is approximately proportional to V −16*
** Color temperature is approximately proportional to V 0.42*
Here’s a graph I found that shows all this
http://lamptech.co.uk/Documents/IN%20Voltage.htm
I’ve been in the business of specifying/designing lighting systems for over 40 years. I used to remember these incandescent calcs but I’ve had to look them all up. We haven’t used incandescent lamps in any quantity for probably 30 years in commercial properties.