Well, worse than I thought too, but then again it still means that HIDs are better upgrade. If you put relay harness in, there's no way you can fool lamp failure detection into ignoring the lack of load with this 1.5V difference. Unless you like the heart-attack inducing chime every time you switch the lights on, or put in a lights-on 70W heater in the engine bay....

Rotodiesel, can you measure voltage drop from the (lit) bulb to the back of headlamp connector (the thin wire)? I know it's tricky with headlamp on, but that'd tell us how much it's losing there (my bet is 0.5V-1V). I cannot measure this because that part of wiring is no longer used

I haven't really got the time to do any further measurements on a functional vehicle but experience tells me that there will not be much voltage lost within the headlamp unit. Although the wires are thin, they're very short.

It's a crappy VAG system which does not meet the requirements of the lamp makers. In the Philips lighting catalogue, the H7 output figures are for a lamp terminal voltage of 13.75V. Some hope on a Superb.

Technically, HIDs are the obvious solution - regulated current draw, largely independent of voltage and lower running current. I'm not going to be drawn on the legalities...

rotodiesel.

Well, worse than I thought too, but then again it still means that HIDs are better upgrade. If you put relay harness in, there's no way you can fool lamp failure detection into ignoring the lack of load with this 1.5V difference. Unless you like the heart-attack inducing chime every time you switch the lights on, or put in a lights-on 70W heater in the engine bay....

Rotodiesel, can you measure voltage drop from the (lit) bulb to the back of headlamp connector (the thin wire)? I know it's tricky with headlamp on, but that'd tell us how much it's losing there (my bet is 0.5V-1V). I cannot measure this because that part of wiring is no longer used

I cant understand why your all so worried about the volt drop, your talking about a 12volt circuit, the problem about a low voltage circuit is more current, more current equals more resistance so the thinner the cable the more the volt drop but as long as the cable is up to the current carrying capacity you require and the voltage is roughly the 12volts that you need there should be no problem, If volt drop is an issue you just have to increase the cable size and this offers less resistance on the circuit and ups the voltage

Look at it this way a 100w lamp on 240volt circuit pulls .4amps, but a 100w lamp on a 12volt curcuit pulls 8.3amps.

I can't give you a physics lesson on incandescent lamp characteristics, but terminal voltage is very important. The light output drops off extremely rapidly with reducing voltage.

This VAG application does not meet the voltage requirement in the Philips data for the H7 lamp so there's no wonder the headlamps are so poor. Most other cars of this size have headlight relays.

rotodiesel.

I can't give you a physics lesson on incandescent lamp characteristics, but terminal voltage is very important. The light output drops off extremely rapidly with reducing voltage.

This VAG application does not meet the voltage requirement in the Philips data for the H7 lamp so there's no wonder the headlamps are so poor. Most other cars of this size have headlight relays.

rotodiesel.

So what your basically saying is that due to the lack of voltage at the lamp terminal the lamps don't work sufficiently, and the design of Philips 12v lamp requires the full 13v+ thats produced by the alternator. If this is so why standardise car voltages at 12volts? Isn't this a bad design by Philips?

The bad design is by VAG. Voltage regulator settings vary as does their temperature coefficient. My car was very hot when I did the tests (just back from a towing session) so the voltage was on the low side. Normally, the regulator on my car will give a battery voltage of 14.2V.

Taking this as a reasonable figure for a calcium grid battery, this leaves 450 mV (nearly 1/2V) to enable the Philips specification to be met. It's not beyond the wit of VAG to design a wiring system which limits the losses to less than 1/2V between the source (alternator) and the load.

No wonder there are so many relay kits around (mostly dubiously engineered) - obviously others have reached the same conclusion.

Car "voltages" are not 12V - you need around 14V to charge a 12V lead acid battery. 12V is a nominal figure used to descibe the system voltage.

rotodiesel.

The bad design is by VAG. Voltage regulator settings vary as does their temperature coefficient. My car was very hot when I did the tests (just back from a towing session) so the voltage was on the low side. Normally, the regulator on my car will give a battery voltage of 14.2V.

Taking this as a reasonable figure for a calcium grid battery, this leaves 450 mV (nearly 1/2V) to enable the Philips specification to be met. It's not beyond the wit of VAG to design a wiring system which limits the losses to less than 1/2V between the source (alternator) and the load.

No wonder there are so many relay kits around (mostly dubiously engineered) - obviously others have reached the same conclusion.

Car "voltages" are not 12V - you need around 14V to charge a 12V lead acid battery. 12V is a nominal figure used to descibe the system voltage.

rotodiesel.

I get what your saying now, I do understand a alternator needs to generate 14volts to charge a 12 battery I was just under the impression the other circuit voltages like the 12volt circuit and 5 volt circuits were regulated, obviously only the 5volt circuit then,

Isnt the VAG wiring system just another example of VAG pushing the limits off every component just to save the odd penny here and there? like the brake pedal switch that can fail when a trailer is connected?

All it needs is higher spec switches and cable but imagine the VAG accountants arses twitch at thought of spending them extra few cents

Just so.

rotodiesel.

I think this discussion has now naturally run its course :lol:

Thanks for the info about the voltage drop though Roto, I guess that's evidence enough to justify a HID upgrade to SWMBO...