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Old 09-25-2008, 04:02 AM   #1
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LED lights

Hello everyone i'm new to the forum

I just got a new car - a reanult clio 1.2L 16v( 60mpg rated)swapped for my old toyota corolla diesel estate(55mpg tops!)

Getting my scangauge today - cant wait to see what i can push this beast to do (70mpg?)

I have also just changed most of the bulbs in the car to LED for longevity and i'm hoping less strain on the alternator so less fuel used

I was wondering - LED headlights, if one headlight is typically 55w - 100w, how much fuel could we save if we had all LED bulbs and LED headlights?!

I never realised it before but one headlight is like running a laptop!!

It must be possible to make LED headlights, those cree LED's are available now with 900 lumen - surely this is enough to use legally on the road?That cree LED is 4.2v and 2.8amps!So the problem is cooling!I recon with all LED bulbs and LED headlights you could easily save 150watts - this would surely have an effect on FE?maybe 5-10 percent?

andy
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Old 09-27-2008, 12:10 AM   #2
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well i think that you could pull it off, but it would all be hand built, 900 lumens is at the max that that emitter can do, and you are dealing with a lot of heat, if you where to have say 4 in on each side that would be 80 watts at 7200 lumens. that would be a nice bright headlight setup(thats as bright as most HID headlamps and a lot brighter than most incan headlamps out there) if you could focus the beam well, the only problems is that you would have to make a driver setup for the led's and heat...

Lots of heat, the cree's make 8?C/w so that 320?C per light of 608?F...have fun with that, if you had a cooling system you might be able to get away with it, and i would love to see someone try once the mc-e come out(they are a 4 die emitter that african_andy189 was talking about, and are coming out some time this month)

by the way i am a flashlight nerd
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Old 09-28-2008, 04:29 PM   #3
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I am an electronic engineer and have built some pretty ambitious projects, a CNC machine for one, But i just don't think it can easily be done, the cooling is a major problem, the LED's will probably just end up being overdriven and have a shortened life from the heat, part of the reason that even auto manufacturers haven't done it successfully yet.And if they're being worn out all the time it kind of ruins the savings you make in fuel.

I think LED's for all the stop/indicator/fog/reverse/number plate lights and HID is more realistic for the headlights.Has anyone changed to HID's and noticed fuel economy is affected?typical HID's draw about 35 watts compared to about 50 for a normal halogen. So that's 2.5amps less draw off the alternator
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Old 09-28-2008, 04:49 PM   #4
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true but thats an alternator that makes 120 amps (typical newer car, some older ones made as little as 60) i think the only way it can make a differenc eis if you did all city driving where the car would be idiling quite often (where alternator makes least amps) but highway/ higher rpm situations it makes plenty of reserve power.

but for those of you who want to drop your idle rpm to a minimum it might help it, like my chevette i notice when i have the lights on and press the brake the headlights dim when at idle. but to be fair i knocked the idle down to 300 rpm. (ive had it at 100 rpm before, kinda scary and quiet because it was still smooth as ever)
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Old 09-28-2008, 05:13 PM   #5
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Quote:
Originally Posted by VetteOwner View Post
true but thats an alternator that makes 120 amps (typical newer car, some older ones made as little as 60) i think the only way it can make a differenc eis if you did all city driving where the car would be idiling quite often (where alternator makes least amps) but highway/ higher rpm situations it makes plenty of reserve power.
That statement directly contradicts what many others on this forum say about alternators, that they do not drag the engine and produce unnecessary power - - instead, their field is turned on and off as necessary to keep the battery charged.
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Old 09-28-2008, 08:10 PM   #6
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what??? ok easy disprove that: disconnect the battery while the engines running, it will stay running and act normal. magic? i think not....alternator is what accually powers your car, battery is there for it to start mostly (also allows you to power stuff when engine is off , etc)

i think i should reword what i said

alternators do drag the engine, BUT at idle where theres minimal engine power (ie engines only turning over 500 rpm) the effects of alt drag are noticeable. but at highway speeds 2K+ the engine is already spinning pretty fast hence spinning the alternator faster thus more easily creating more amps.

(remember back to grade school days moving a magnet slowly in a coil of wire and watching a needle refract a tiny bit? then move it really fast and the needle goes wild? same kind of principle)

some of you in the "older crowd" remember way back when cars had generators? at idle the headlights were dim then you rev them they get brighter? kinda works like that...
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Old 09-29-2008, 05:35 AM   #7
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Some people are forgetting about how an alternator is wired. The positive wire goes to the battery AND the primary fuse block/wiring harness - takin the battery out of the equation doesn't matter (but, if you're fuel injected and you attempt to pop off the positive post, have somebody stop the engine before you hook it back up - the voltage spike from hooking it back up might fry your computer).

If it spins, it's putting drag on the engine. Period. How much varies. Water pumps, alternators, idlers, tensioners, power steering pumps, etc. - they all put a drag on the engine, but how much does vary.

The alt will always do it's best to produce maximum amperage, but the sense wire and voltage regulator are there to keep your electrical system intact and the battery alive.
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Old 09-29-2008, 05:47 AM   #8
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Continuing thoughts from the previous two posts, the voltage regulator is key. A voltage regulator reduces the alternator's field winding current when the voltage get too high. This reduces the alternator output. Without a voltage regulator, an alternator would fry the battery.

Reducing any electrical usage will improve mileage a bit. But, there will always be drag from the belt drive, bearings and cooling fan. I've often thought that an alternator should have a clutch like an A/C compressor to reduce drag. With a clutch, the alternator would charge the battery only when it got low and/or during braking; this would eliminate alternator drag.
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Old 09-29-2008, 07:37 AM   #9
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Quote:
Originally Posted by jeep45238 View Post
(but, if you're fuel injected and you attempt to pop off the positive post, have somebody stop the engine before you hook it back up - the voltage spike from hooking it back up might fry your computer).
Why would you get a voltage spike when reconnecting the battery? The battery is 12v. If anything, you get a spike when you disconnect it from the alternator regulator not responding fast enough to the battery being gone. The battery is more of a regulator / buffer than anything else when the car is finally started unless your alternator is low on output then the battery provides some juice.
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Old 09-29-2008, 09:40 AM   #10
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Quote:
Originally Posted by VetteOwner View Post
what??? ok easy disprove that: disconnect the battery while the engines running, it will stay running and act normal. magic? i think not....alternator is what accually powers your car, battery is there for it to start mostly (also allows you to power stuff when engine is off , etc)
This has been my understanding for a long time. I have heard otherwise but have never actually done the experiment. I think maybe I need to rephrase, or at least emphasize....

Quote:
Originally Posted by theholycow View Post
That statement directly contradicts what many others on this forum say about alternators, that they do not drag the engine and produce unnecessary power - - instead, their field is turned on and off as necessary to keep the battery charged.
Quote:
at highway speeds 2K+ the engine is already spinning pretty fast hence spinning the alternator faster thus more easily creating more amps.
But is it actually making those amps, and therefore putting that drag on the engine? Common knowledge on here, which I didn't know until I arrived at this forum, is that it does NOT; instead, as less demand is placed on it, it drags less. This would mean that at higher RPM it would eat less torque, I guess.
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