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Post by vins0101 on Oct 27, 2023 19:45:02 GMT
Hi guys,
I wanted to ask if it’s possible by a coding that automatically turns off the headlights during the engine starting phase (both from the key and from stop&start), and then turns on them back on when the engine is running. In summary, turn off when cranking.
I think it would be useful to preserve the life of the headlight bulbs.
Thanks in advance,
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Post by dv52 (Australia) on Oct 27, 2023 21:48:36 GMT
vins0101: Hi. Why do you believe that illuminating the headlight lamps during emgine-cranking compromises their longevity? Battery rail volts falls during engine-cranking because of the large electrical load and I would have thought that any short-term voltage spikes that might be generated would be immediately suppressed by the low impedance of both the battery itself and the starter motor! What am I missing? Don
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Post by vins0101 on Oct 28, 2023 13:06:46 GMT
Hi Don,
therefore the lamps are not affected by the engine starting phases.
Would it therefore be advisable to turn off the headlights, to avoid that, in addition to the load on the starter motor, the load from the headlights being switched on is added to the battery?
In any case, do you think the proposed change is unnecessary?
Also, if I were to change the bulbs from halogen to LED, does nothing happen when I start with the headlights on?
Thanks,
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Post by dv52 (Australia) on Oct 28, 2023 21:25:23 GMT
vins0101 : hmm....... I'm not sure why these concerns have arisen - of course, stuff like turning-off the headlights while engine cranking (particularly, cold-engine cranking) helps because the electrical load on the battery is reduced. However, the benefit is marginal only and a healthy battery shouldn't require this extra step.
This is especially true on modern cars (including mk7s) - think about how Start-Stop works. SS was first introduced by VAG in 2006 as "Bluemotion". SS cranks the engine many, many times during a trip.
Over the 17 years that SS has operated on countless cars (both VAG built and other manufacturers) - you won't find ANY reports on forums that indicate a systemic shortening of headlight longevity on these cars! The deafening silence speaks volumes about this matter - IMO, of course!
As for your lamp-life question - again, turning-off the headlights would technically increase the longevity of the headlight bulbs - but, once more - at the margin only!! Modern headlight lamps are fit-for-purpose - meaning that their longevity has (or rather, should have) a suitable life-cycle. Yes, not all headlight lamps are built the same and not ALL individual lamps have the same longevity - but the manufacturing principle of fit-for-purpose is uniform!
Plus, ALL mk7's that are factory built with halogen headlight fittings have Daylight Running Lights - which can't be turned-off whilst cranking.
If you want numbers as an example - consider this:
The load placed on a battery when cold engine-cranking varies - but 500 amperes is a good rule-of-thumb number (note: this load is only drawn for about half a minute). During the engine cranking process, the battery rail voltage should NOT fall below 7.2 Volts.
On a Golf mk7 with halogen headlight fittings, the lighting load from the DRLs is 30Watts (i.e. a 15W lamp on each car-side). At the cranking voltage of 7.2 V, the DRL load on the battery draws an additional 4 amperes. Said another way, the DRL load is less than 1% of the starter motor load!!!.
And even if the low-beam lights are switched-on when cold cranking (i.e 2 x 55Watt lamps), the equivalent number using the analysis above is an additional load of around 3%
Finally- with regard to your question about retrofitting LEDs - the main reason why folk do this is to get better illumination. If the objective for changing to LED lamps is better cranking - save your money!!!
Bottom-line: with absolutely no offense intended - my suggestion is, worry about more important issues!!! 
Don
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