Next (stupid) question...................

If the DLR lights were turned off, and the car was only used in daylight, what is the drain on the alternator compared to having DLR lights on during daytime and some/lots night driving?

If charging a battery cost £56 a year in fuel (at present-day prices) it must cost more to supply all the lights.

Dunno about the total wattage specifically without looking it up, but maybe two headlights at 55w each, plus two tail lights at 15w each and numberplate lights too.

Say 150 watts total during darkness (not including fog lights or wipers)
12v @ 150w is 12.5 amps.

How does that compare to keeping and charging a battery during daylight?

Thanks,
Mick.

Mick F said:

Next (stupid) question...................

If the DLR lights were turned off, and the car was only used in daylight, what is the drain on the alternator compared to having DLR lights on during daytime and some/lots night driving?

If charging a battery cost £56 a year in fuel (at present-day prices) it must cost more to supply all the lights.

Dunno about the total wattage specifically without looking it up, but maybe two headlights at 55w each, plus two tail lights at 15w each and numberplate lights too.

Say 150 watts total during darkness (not including fog lights or wipers)
12v @ 150w is 12.5 amps.

How does that compare to keeping and charging a battery during daylight?

Thanks,
Mick.

Click to expand...

It's not large, but it is measureable; depending on the speed you're travelling, it'll likely cost you somewhere between 1 and 4 mpg. It's one of those rare situations where the extra fuel needed when running with the lights on is greater the slower you go!

746 watts = 1HP; in practice, there are always some losses, so your 150 watt load is going to take about an additional 1/4HP from the engine.

Very roughly, theoretical calculations suggest that will burn about an additional tenth of a litre of petrol per hour. At 50mpg, a tenth of a litre will take you just over a mile.

Another way of looking at it is that running with all the lights on will reduce your full-tank range by about ten miles.

Conclusion: leaving just your DRL's on will likely cost you more in replacement bulbs than it does in fuel.

That said, I've often wondered if I'd have been able to average over 60mpg in my 1.2 with the DRL's on?

jrkitching said:

746 watts = 1HP; in practice, there are always some losses, so your 150 watt load is going to take about an additional 1/4HP from the engine.

That said, I've often wondered if I'd have been able to average over 60mpg in my 1.2 with the DRL's on?

Click to expand...

UFI has LED DRL's. Non-'Canbus' types that draw a total of ~14W. Although these did initially set off the bulb out warning intermittently, it seems the BCM is a learning unit as I can barely recall the last time I had the warning.