Newb LED driver question

OK, here I go, dipping a toe into led lighting.....

Im yearning for an LED light bar for my truck, but they are way too expensive, so the 'build one' mentality has taken over.(I did electronics when I was younger, I remember a little.....)

OK, Ive bought a few luxeon III emitters(on a star base) to dabble with.
If I link 4 of em in series on a 12v car battery, they are brightish, with a collector(collimator) a little better, but I know with a proper driver I can get em B R I G H T!

Whats the best option? a driver per led? daisy chain em in batches of 2 or 3 per driver?

Am I using the best LED's for the job? they seem to have a decent output, and are cheap enough, but if there is a much better option for only a few quid more, then that would be better. I need lots of light, focussed in a nice tight beam. Running maybe 20-40 leds........

Ive used search, but there is so much information, which quite franbkly I dont understand a lot of, its hard to determine whats the best way to go.

Rollazuki.

Cmon guys, help a fella out.
A little pointing in the right direction would do, am I better using a certain type of led for that application? Would anyone know of the best(most cost effective) led driver to run?

Try these LEDs, (Cree XPG R5's) not the cheapest, but theyre really great! Also, Luxeon III's are pretty out of date..... technology is always advancing!

http://www.cree.com/products/xlamp_xpg.asp

I didn't understand this, did you want 30-40 LEDs to produce a BRIGHT light? I'm pretty sure a couple of these will do the trick . I'm not too sure about the driver.... Maybe someone else can help on that! But I'll do a little research myself later....

buck puck as driver ... i just got some for a similar application

OP: Why would you want to spend time and money on a LED truckbar when you should have all the power you need to run halogen lamps?

I put 8 Lux III's in parallel. Handles 9v nicley!!!



Big metal plate for heatsinking.
You could also try an SSC P7? (HEATSINKING!!!)

EDIT: photos deleted for now. Too big! Hopefully they'll be re-posted sometime soon!

rollazuki said:

I need lots of light, focussed in a nice tight beam. Running maybe 20-40 leds........

Click to expand...

Pick a beam angle - reflectors and optics list the width to half strength. An 8 degree optic will have most of its light within 8 degrees of center.

Pick an amount of light. This will tell you how many LEDs you'll need. You'll need a reflector and/or an optic for each. Consider what current you want the LEDs at. Running them at spec or above spec is bright, less efficient, and requires fewer LEDs. Run them below spec for longer LED life and more efficient lighting. Let's say you want to run X-REs at 350 mA, which are good for about 100 lumens. You want 2200 lumens, but remember that optics and reflectors cut light out, maybe 10% or so. Call it 24 LEDs (2400 emitter lumens).

Consider the forward voltage of the LEDs (3.2 to 3.7v usually) and your supply voltage, and the voltage drop of your driver. Buck drivers are popular because they can be more efficient, and also won't suck a defenseless battery dead. Buck drivers decrease voltage and regulate current. Let's say you have a driver with a 1v voltage drop. With the alternator running you've got 14v, with it off you'll have about 12. So you have 11v for LEDs, which will really only run 3 LEDs. That's how many you can have in series.

Number of LEDs divided by number in series = parallel chains. Multiply the number of chains by the current per chain to get the current rating you need on a driver. 24/3=8, 8*350mA = 2800mA or 2.8A. You'll need a driver that will deliver that amount of power - it'll take care of the voltages as long as it gets enough battery voltage for the LEDs and its voltage drop.

The driver will dissipate (Voltage drop) * (current) watts, in this example 2.8 watts. The LEDs will take (current) * (voltage per LED) * (LEDs per string) * (Number of strings), in this example (2.8A*3.2V*3*8) = 215 watts. This is how much each set has to be heatsinked for - better to have too much heatsink and be ok on hot summer nights (No running lights in the daytime, eh?) than to skimp on aluminum and have to replace your LEDs.

Cost: About $30-$50 for a driver, about $5 per LED, and the heatsink is up to you. Let's say wires are free, that's about $160, but you've got to get your optics or reflectors (24 of them!). Using fewer LEDs at higher current, or higher-output LEDs (like the XP-G or such) reduces number of reflectors to buy. It's all a tradeoff.

thanks for the very useful replies. I appreciate there is power to spare on a car, and maybe some kinda incan, or hid would be suitable, but I know less about hid than leds, and they appear more expensive to do.
I also have my heart set on leds. The general appearance of visionx/rigid lightbars really appeals.
Where in the uk is the best place to source crees and buckpucks? Dissapointingly, ebay has failed me!!!!!
hopefully an aluminium housing should provide sufficient heatsinking.

Basically I want a kickass roof light system that puts 'lightforce' lamps to shame.....

Seems to me that you want to research the following items.

Taskled - Hyperboost Driver (will drive 20 XPG's @ 1amp, you will need two.)

Ledil - CXP square optic. Can easily be setup in a hosing similar to the Rigid and VisionX and are smaller than the optics that they use.

Cree - XPG R5 LED's

All of these items can be found at Cutters.

symbology said:

Seems to me that you want to research the following items.

Taskled - Hyperboost Driver (will drive 20 XPG's @ 1amp, you will need two.)

Ledil - CXP square optic. Can easily be setup in a hosing similar to the Rigid and VisionX and are smaller than the optics that they use.

Cree - XPG R5 LED's

All of these items can be found at Cutters.

Click to expand...

Also.... If you're actually going to buy 40 XPG's.... There will be a pretty big dent in your wallet.... Theyre currently selling XPG's on 10mm boards at Cutter for ~$21 including shipping to the US....oo: so 21x40= (~$840!!) Someone please correct if I'm wrong. I had to do this post fast!!

With shipping to the US they are $270 USD.

rollazuki said:

Cmon guys, help a fella out.

Click to expand...

I personally would have posted in the automotive or electronics forums - there's usually greater response there. You could ask a mod to move it. As for drivers, see my tagline.

Coast, your pics are oversize.

COAST said:

Also.... If you're actually going to buy 40 XPG's.... There will be a pretty big dent in your wallet.... Theyre currently selling XPG's on 10mm boards at Cutter for ~$21 including shipping to the US....oo: so 21x40= (~$840!!) Someone please correct if I'm wrong. I had to do this post fast!!

Click to expand...

Too fast - you're wrong. Try adding 40 of them to your cart, not just one and multiplying by 40.

For running in a car, it isn't insane to forget the driver and just use a resistor (or several of them). I'm not saying this is 'the best' way, just one to consider.

The only problem is that the brightness is impacted by whether the engine is running (battery charging, around 14.6V) or not (13.2 early on, 12V or less if you actually manage to drain the battery some).

If you had strings of 3 LEDs, for around 3*3.6V = 10.8V, you'd have to drop 3.8V while the engine is running, and about 2.4V when it's off. This would be a 37% decrease in light output. That's not as much as it seems. My dive light has 5 levels, each 50% less than the next brighter one. That's really overkill, and I'm planning to change to 3 levels, each 75% less than the one above.

However, since you have lots of power, why not use strings of 2 leds, then you have 7.2V on the string, and 7.4 or 6V to drop on the resistor. Now it's less than 20% drop when you turn off the engine, barely noticable. While this approach is less efficient (around 50% instead of 80-90% efficiency with buck drivers) it has two advantages: it's cheap and it won't be damaged by automotive electrical environment, which is pretty harsh.

On the subject of automotive environment, I would STRONGLY advise you to check on whether your intended driver is rated for automotive use, or at least whether others are using it that way. There are large, long surges, called 'load dump', as well as transients and noise that wreak havoc with (i.e. destroy) otherwise highly reliable devices. Maybe the automotive electronics forums will have more information on this.

AnAppleSnail said:

The driver will dissipate (Voltage drop) * (current) watts, in this example 2.8 watts.

Click to expand...

If you are looking at buck drivers, trying to do power calculations, you probably won't find data about 'voltage drop'. You will much more likely find 'efficiency'. To calculate power loss in the driver, the easiest equation may be:
P = (1/E -1) * Po, where
P = power loss in the driver.
E = efficiency; if efficiency is %, then divide by 100, so 85% becomes 0.85.
Po is the output power. This is the total output voltage times current.
Of course if you read my previous post and are substituting 'resistor' for 'driver' then you probably are interested in 'voltage drop'...

AnAppleSnail said:

The LEDs will take (current) * (voltage per LED) * (LEDs per string) * (Number of strings), in this example (2.8A*3.2V*3*8) = 215 watts. This is how much each set has to be heatsinked for - better to have too much heatsink and be ok on hot summer nights (No running lights in the daytime, eh?) than to skimp on aluminum and have to replace your LEDs.

Click to expand...

I think there's an extra factor of 8 in there. You use 2.8A total for all strings, then multiply by the number of strings.
The correct calculation can be done several ways:
2.8A total * 9.6V total = 26.88W
0.350A/string * 8 strings * 9.6V = 26.88W
0.350A/LED * 3.2V * 24 LEDs = 26.88W
I'm going by the seat of my pants here, but I don't think that you'll have any trouble dissipating that amount of heat on any kind of aluminum bar that spans the width of a vehicle.

TorchBoy said:

Too fast - you're wrong. Try adding 40 of them to your cart, not just one and multiplying by 40.

Click to expand...

Awesome! Thanks for the correction! Like I said.... I was in a hurry! :thumbsup:

Coast, your photos in post #5 are too large - please resize them (see Rule 3)

Ah, ok. Sorry DM51! I'll just remove them for the time being, then re-post them when theyre resized..... Thanks.