LED and driver question

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IkiptagaI-ENigma

Newly Enlightened
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Oct 14, 2009
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Good morning folks, I'm new to building projects with LED's, so here I am with a couple questions.

I'm looking at building a custom headlight for my bike, and am looking at Cree XR-E Q5 LED's for use. I am hoping to use 4 of these together, two with spot lenses and 2 with wide angle lenses, so that I can have a path of light that illuminates the ground in front of me properly.

I know the Q5's are 3.7v, and I have found I can get 3.7v Li-Po battery cells for cheap. What would be a good driver to use, and do I need more than 1?

I plan to have the lights mounted in a way as to dissipate heat through the housing, so heat shouldn't be a concern.

P.S. Since some of you are undoubtedly looking at my username and wondering WTF?? I'll tell you only this. It's a riddle. 5 points to he who figures it out.
 
personal advise:
forget spot and wide angle. wide angle focusing is totally useless and a waste of light.
Use all spots and align the beams differently (f.e. two to the sides and down, 1 forward and a bit down, one forward. Or two to the sides and down, two to the sides and up, with an overlapping in the middle)
Key is not to use too much angle, so the main beams still overlap a bit
(= makes 4-6 degrees offset at max, as most spot lenses are 8 deg)

also, much better were to wire the led in series and use a step-up driver.
with 3 or 4 led, the best way (imho) is a 7.2 V Li-Ion Camcorder pack (Canon BP945),
with 5 led, the best way were a 14.4 V Li-Ion battery.
OR, use these poor led in parallel from a 7.2 V Camcoder Pack and use a step-down driver for a Seoul P7 led --> that will give enough current to power all of them.

but then, the - as now - "usual" advises:
1st: with a bit of waiting, the Cree XP-G will be available, so why use the "old" Q5?
Why individual led anyway? (I have, till now, not seen any light where it makes sense, except from mine, where the beams are not aligned parallel. Description of how the individual beams are set, one finds above)
2nd: by purchasing the very cheap Dealextreme bike light, You get most of the parts needed for building a whole light system, all already in a working light.
If need/wish ever arises to mod it: very nice "original" to start modding from
 
yellow said:
personal advise:
forget spot and wide angle. wide angle focusing is totally useless and a waste of light.
Use all spots and align the beams differently (f.e. two to the sides and down, 1 forward and a bit down, one forward. Or two to the sides and down, two to the sides and up, with an overlapping in the middle)
Key is not to use too much angle, so the main beams still overlap a bit
(= makes 4-6 degrees offset at max, as most spot lenses are 8 deg)

also, much better were to wire the led in series and use a step-up driver.
with 3 or 4 led, the best way (imho) is a 7.2 V Li-Ion Camcorder pack (Canon BP945),
with 5 led, the best way were a 14.4 V Li-Ion battery.
OR, use these poor led in parallel from a 7.2 V Camcoder Pack and use a step-down driver for a Seoul P7 led --> that will give enough current to power all of them.

but then, the - as now - "usual" advises:
1st: with a bit of waiting, the Cree XP-G will be available, so why use the "old" Q5?
Why individual led anyway? (I have, till now, not seen any light where it makes sense, except from mine, where the beams are not aligned parallel. Description of how the individual beams are set, one finds above)
2nd: by purchasing the very cheap Dealextreme bike light, You get most of the parts needed for building a whole light system, all already in a working light.
If need/wish ever arises to mod it: very nice "original" to start modding from
Click to expand...


I can understand starting with a pre-existing, but I suppose I should probably expand on what I said earlier. What this is going on is a bike and trailer combo. The end goal is to have a strong headlight, taillights on the bike and trailer, "marker" lights on the sides of the front rack, rear rack, and on the trailer. In addition to that I plan on using HDPE tubing with a 5mm LED in each end to light up portions of the bike and trailer at night.

If running the LED's in series at a high voltage would produce the best results, cool. What driver would you recommend? As for the Q5's and lenses, Q5's are cheap and put out enough light for me. The arrangement planned is 4 across, with the 2 spots in the middle and the 2 wide angle or diffusers on the ends. The reason for this is that the bike is motorized (66cc 2 stroke), and when I am going down the road at speed, I want to be able to see whats on the sides of me, like I would in a car. I was hit on a bike in my younger years, in broad daylight, when a driver claimed to not have seen me. I have no intention of repeating that experience night or day.

All in all, there will be 26 5mm LED's, 4 Q5's, and I'm as yet unsure what I will need in the taillights, as I intend to do tail/brake lights on the bike and trailer. Suggestions for that would be great.

Information I need at this point, is what driver(s) would be best for the Q5's, what voltage would be ideal for the entire setup (I know I can get voltage steppers to reduce voltage for the 5mm's), and what would be a good setup for the tail/brake. I don't need multi voltage for the headlight assembly, as the bike will only be doing around 30-40mph, and steady light will suffice in place of low and high beams. If anything, I would have the outer lights (wide angle/diffused) on a separate switch from the spots, so that I can switch the spots off in the city.
 
Hopefully this post is in order, as my posts are awaiting approval by moderator...


As I said in the last post, I'm anticipating probably 36+ LED's. I just did a mental count of everything, and I believe I'm looking at 70 total, not including brake lights.

4 of those are the headlights (Q5's), which I think (based on the above poster saying to wire in series) I will have the middle 2 (spot lense) wired in series and the outer two (wide angle/diffused lense) wired in series on separate switches, allowing for city and highway. This would be 7.4v per pair.

The other 66 (5mm) will be run at whatever voltage is native (2.0-2.2 for amber/orange and red).

The Q5's would run from non-adjustable drivers (1 per pair), and the 5mm's would be run from a voltage reducer and diodes.

Could someone tell me what driver I would need for the Q5's, and if the above suggested would be proper for the 5mm's?


The Q5 pairs should run 750mA per pair, if wired in series, and the 5mm's are 20mA continuous/50mA peak if what I found is correct. I plan to use Li-Po battery packs, 4x 10Ah 3.7v units in series (14.8v total).

I entered the info into http://led.linear1.org/led.wiz and it shows me to run my 5mm's in runs of 6 in a series, 11 total series. It shows me that the 5mm's will pull a total of 385mA, making for a total of 1885mA (1.885A) with all 66 5mm's and all 4 Q5's running at once. Figure a draw of 2A flat when the brake lights are applied (not often).

Assuming I have everything above correct, what kind of run time might I expect with the above running on the 4 10Ah batteries @ 14.8v?
 
Information I need at this point, is what driver(s) would be best for the Q5's, what voltage would be ideal for the entire setup
Click to expand...
Wrong way to decide
;)
but dont mind, thats the usual "error"

YOU decide what voltage You want for Your system (Battery chemistry, power needed from light, charging equipment)
and THAT determines - more or less - what drivers and led setup has to be chosen
 
I was originally planning on 4x 3.7 10Ah batteries, but for the sake of low cost and extended runtime, I might instead go with a 12v 20Ah motorcycle battery (model number 18L-BS from Napa).

I know for sure that I want 4 total leds for the headlamp, setup in 2 sets. I initially wanted to do full coverage lighting for the bike, but I think I will step that idea down a bit to wrapping around the front and rear racks, and around the bike trailer. That will put me at around 30 5mm LED's, 20 of them amber/orange, 8 red. http://led.linear1.org/led.wiz tells me strings of 5, with a 56ohm/.25w resister on each string for a 12v power source.

For the headlight assembly, I still want 4 total LED's. I'm looking on ledsupply.com and am wondering if Luxeon TFFC K2's would be better than Cree Q5's? I believe the BuckPuck would work for each pair of lights.

Does this sound like a better setup (for the headlight circuit, obviously, as the 5mm's can be easily set for whatever voltage I run)?
 
Last edited:
IkiptagaI-ENigma said:
... for the sake of low cost and extended runtime, I might instead go with a 12v 20Ah motorcycle battery ...
Click to expand...
With respect, you sound like a glutton for punishment. Those things are heavy. You are talking about a bicycle, not a motorbike, right? You said you can get Li-ion cells cheaply, so why even consider lead for the sake of low cost?

IkiptagaI-ENigma said:
I'm looking on ledsupply.com and am wondering if Luxeon TFFC K2's would be better than Cree Q5's?
Click to expand...
yellow has already mentioned the Cree XP-G, available up to R5 bin.
 
TorchBoy said:
With respect, you sound like a glutton for punishment. Those things are heavy. You are talking about a bicycle, not a motorbike, right? You said you can get Li-ion cells cheaply, so why even consider lead for the sake of low cost?


yellow has already mentioned the Cree XP-G, available up to R5 bin.
Click to expand...

The 12v battery I mentioned is a motorcycle battery, considerably lighter than a car battery. Also a good deal cheaper than the Li-Po setup I previously mentioned, and more tolerable to charging (any car battery charger will work).

Yellow also mentioned that with a bit of waiting the XP-G would be available, meaning that they aren't out yet. In the mean time, the Q5's and K2's are currently on the market, and for cheap. I'm trying to do this for (fairly) low cost with what's currently available.

Yes I am talking about a bicycle, as opposed to a standard motorbike. I'm not so worried about weight, as I'm used to carrying heavy bags, loaded racks, and bike trailers (not necessarily all at once though). Most of the time I go out, I have my bike trailer with me, so it's not such a big deal to put the battery in there.
 
The car batteries I'm familiar with are 40-50 Ah, so yes, it'll be lighter than those, but the 20 Ah SLA I have is still several kilograms, and would be several kilos more than I'd want, even on a trailer. Yes, charging might be easier but do you really need that many watt-hours?

I tend to agree with yellow that it seems more sensible to figure out how large a battery you need for the runtime you want. That way you can keep weight to a minimum - surely that's important? What are you trying to achieve with all this lighting? A week's worth of night cycle touring without needing to recharge?

The XP-G is currently available and shipping (did you bother checking?), and many would say it's very low cost, especially for what it gives you. Its high efficiency means you could use a smaller battery for the same illumination - surely that's important?
 
The motorcycle battery will serve other purposes in addition to the lights. I've been looking at cheap GPS units, such as TomTom units, that are good as a map and a speedometer. The battery will serve to power the lights, the GPS, and my iPod as well (when it needs it). I was considering the Li-Po batteries for the lights alone, but I figure I'll be better off with a single battery for everything.


I did a Google search for the XP-G, and the only thing I'm finding is pre-orders. If you know a place that sells them, and perhaps a spec sheet or comparison to the Q5 or TFFC K2, I'd gladly take a look.
 
Just putting my penny worth in...

I've doing my first bike light and have chosen the Taskled Hipflex driver cos it sounds so reliable. Ive trawled this site and ín the end decided i wanted reliability and performance over cost. The DX and KD ones are cheap and you could take a chance buying a couple.
I've chosen to run x2 MCE's (from KD) focused by BOOM-MC-S reflectors (from digi-key).
This is going to be powered by x6 18650 Li-ion batteries (from DX) wired 3S2P to give 11.1V and 5200mAh. Battery holders are hard to come by for 18650's though but I did find some on digi-key.
This setup should be bright enough for off-road but if you are on-road you'll blind the traffic!!!

Unfortunately KD and DX are Slow Slow Slow (which I fully expected for the price) so I won't be able to show you the finished article for some time.

Oh ... and I'd take yellows advice ... the DX bike light is a great start and you could mod from there at a later date.
Be warned that the cost of a custom one add's up fast. I've not totted it up but i've gotta be pushing 100-quid for mine and its not finished!!!
 
Last edited:
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