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Thread: How many LED's

  1. #1
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    How many LED's

    HI all. I have ben a long time member and have enjoyed the help and creativity on this forum. So far i have made my own led lights using the simple and proven formula of a cutter triple and a 14.8v LiPo with a buck driver. It has always proved to reliable and effective. I want to get a little more creative now and design something new. Currently i was thinking of a 7.4v battery because they are so much cheaper and lighter also. So this will mean a boost driver. My big question is what led configuration should i go for if i want more light output and quality than the standard 3 led. Is a quad the way to go or is it not worth the small gain like i have been reading in the forums. Can i get better results from 3 with different reflectors, or perhaps less leds and better reflectors higher output VF.
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  2. #2
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    So we have a point of reference, what LED's and bin are in your current light? Do you use a single light, or a bar / helmet combo? What kinds of trails do you typically ride. Tight and twisty? Wide open and fast? etc.....

    What's your goal in terms of how much brighter? Generally speaking, you have to double the number of lumens to make a very noticeable difference in the perceived quantity of light. What's your goal in terms of runtime?

  3. #3
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    If the controller is a real boost converter and not some other topology that outputs a higher voltage than its fed with, then you will need a combined diode Vf >> Vbattery.

    Basically 3 leds in series will be app 11V vf when running at full current, but will start to operate at probably around 2.5V/die. This means a couple of things.
    1) The boost converter will not be able to go to zero brightness since the battery is always connected to the LED string via a diode.
    2) It will have trouble controlling lower forward currents since it will by default always conduct a little. (might squeal a little or lights might flicker)

    Either run lower voltage battery or put more LED's in series, for my 3 led series strings run in series from a boost converter, they start to light on their own with a bat voltage greater than about 6.8V.

    So I use 4 NiMH cells in series to give me a 4.8V nominal pack. Also this pack is more like 6.3V when fully charged.

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    IMO this is probably the key question for DIY at the moment: how many LEDs?

    Right now the P7 single LED with four diodes on one die is predominant due to it 'bang for buck' appeal.

    The problems with the P7 appear to be:
    1) it is that it is not very efficient in lumens per watt terms.
    2) most designs can't run at the full rated 2.8A (ie most only produce 500-700 lumens from the LED) due to insufficient cooling.

    The current range of XP-G LEDs (and the coming generations) when coupled with integrated drivers (per Quazzle and Cutters) will make for greatly improved performance in terms of:
    a) better battery life due to better lumens/watt particularly when running at reduced current.
    b) smaller lights due to better cooling (no driver cavity in the back of the light stuffing up the thermal path).

    When both my MS and seven LED XP-G light are set with the same power consumption the seven LED XP-G totally leaves the MS for dead.

    Summary:
    1) Multiple (decent) LEDs are better (more efficient particularly when run at reduced current).
    2) Integrated drivers are a must IMO (unless price is the compulsion - in which case buy a MS).

    IMO the DIY sweet spot now would be a dual triple, something like this: Double L332MC build.. A single barrel of that leaves would leave a MS for dead. Easy to fit wide optics in one barrel and narrow in the other. Chur.
    Last edited by Mark2c; 07-22-2010 at 04:35 PM.

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    Quote Originally Posted by mercman
    ...simple and proven formula of a cutter triple and a 14.8v LiPo ...
    Are you sure? The piccies looks like lithium ion batteries (18650s maybe?).

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    Further details

    Thanks for the response guys. This is great feedback. So my current system runs cutter triple xpg with the kit optics that come with. I'm running a 14.8v 2600mah batt through a taskled buck driver. Gives me about 4 hours on 1000mah. I use for the commute and night rides on the local cross country courses. I was thinking of running the new system brighter and do a bar as well as the helmet. I like the double up of two triples you suggest. I guess I'm wanting to keep the efficiency's there. I don't want to go overboard for to little gain.

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    Mark2C light

    thats an awesome light you've made. What size are those optics. Im currently using the 35mm diameter. I've always thought that the wider optics will provide more light as well as better quality of beam for the same power. Lately im not so sure.

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    Quote Originally Posted by mercman
    thats an awesome light you've made. What size are those optics. Im currently using the 35mm diameter. I've always thought that the wider optics will provide more light as well as better quality of beam for the same power. Lately im not so sure.
    No na no! Unfortunately it isn't my light. It was made by a guy who lives about 500 miles north of me. I loaned him two boards and optics as his are on back order. The optics are 20mm (the thread has all the info).

    The smaller size on the helmet easily offsets the superior beam forming potential of larger lights.

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    Mark2C

    Oh so they are your boards/led configurations. Nice. that resolves the whole heatsink issues around the boost drive.. So do you have a website i can look at to check them out.. How much and are you making them etc.....

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    www.Lux-rc.com

    Info attached.
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    Quote Originally Posted by mercman
    Oh so they are your boards/led configurations. Nice. that resolves the whole heatsink issues around the boost drive.. So do you have a website i can look at to check them out.. How much and are you making them etc.....
    Just to be clear, Mark2c doesn't make these boards. They are designed, mfg and sold by Quazzle (mtbr screen name). Mark2c simply purchased some and was kind enough to let bshallard borrow them for his light build.

  12. #12
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    Thanks JM - totally correct. Sorry, I didn't see mercman's next posting.

    Quazzle's site is www.lux-rc.com

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    boards

    THanks guys. they are a nice unit. It makes total sense to combine the two. Led and driver. Its making me rethink my housing design now...

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    Once I've identified a suitable source of sapphire glasses and seals I will post an open source CAD drawing based on bshallard's that will allow you to go to any competent machine shop and say "how much for one of those?".

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    20mm or 35mm

    so ive been thinking about my new led configuration and im stuck on one last question. Would a 3x XPG led with 20mm optics produce the same or less brightness of 3x XPG led with 35mm optics.

    So far im settled on the 3x XPG's with a 7.4V battery system. I guess the driver will depend on the efficiency of 20 to 35 mm optics... Im thinking if 35mm is better then ill go with a maxflex....

  16. #16
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    A 20mm triple XP-G will probably "appear" like it's not quite as bright. Won't have quite as much punch as that 35mm setup.


    I'm running a Lux RC L332MC 20mm triple on the bars with a frosted medium Carclo 20mm optic. I run 2x single XP-G's with Regina reflectors on my helmet to give me some distance. This setup is really turning my crank lately. I switched from a narrow to medium on the triple tonight and really love how it compliments my double barrel Regina.

    I highly recommend it!

  17. #17
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    Quote Originally Posted by mercman
    so ive been thinking about my new led configuration and im stuck on one last question. Would a 3x XPG led with 20mm optics produce the same or less brightness of 3x XPG led with 35mm optics.

    So far im settled on the 3x XPG's with a 7.4V battery system. I guess the driver will depend on the efficiency of 20 to 35 mm optics... Im thinking if 35mm is better then ill go with a maxflex....
    The smaller optics are always flood and don't give a decent hotspot, even worse with the XPG.
    The 35 will be twice as bright as the 20 but a narrower spot.
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  18. #18
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    Quote Originally Posted by mercman
    so ive been thinking about my new led configuration and im stuck on one last question. Would a 3x XPG led with 20mm optics produce the same or less brightness of 3x XPG led with 35mm optics.

    So far im settled on the 3x XPG's with a 7.4V battery system. I guess the driver will depend on the efficiency of 20 to 35 mm optics... Im thinking if 35mm is better then ill go with a maxflex....
    Mercman can clarify if this is wrong, but I think he may be asking about a setup using 3 separate 20mm optics. Not a single 20mm triple optic.

    My testing has shown that 3 20mm individual optics will be an improvement over the 35mm triple, in term of total light put on the ground. But, I'd estimate it as only a 10 to 15% improvement. Which is not enough to really make any real difference in any case except when you're comparing the two side by side. But, if you're starting a design from scratch and you don't care about the additional size, there no reason not to go that route.

    The biggest advantage in my opinion for the individual 20mm optics is to customize the beam pattern for those where the 35mm triple beam pattern isn't optimal. That's not the case for me because the 35mm pattern is just about perfect for twisty east coast singletrack. But in places that are more open, more throw would be better. You can get that with individual 20mm optics and have a lot more flexibility by mixing different optics.

  19. #19
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    tops

    yep thats pretty much was i was asking. My current setup is a 35mm triple XPG and at low power 700mah its as bright as a magicshine. On high, well there's not much brighter that i have seen. Now im looking at refining the beam patterns to get a bit more throw. The XPG triple narrow 35mm beam is good but i think it vould be better. Also i want to put a led on the bar for better depth perception in cross country races and as a backup light. So at the moment im thinking about a single xpg on the bar in wide beam and a single xpg on the helemt. Perhaps two, im not sure as it requires a whole new light housing design. This could all run off 7.4v batterys with a buck driver. Again im stuck on 20 or 35mm optics though. Even a single led with a 35mm optic would be brighter than a 20mm at say 1000mah. I guess one aspect driving this design is bang for buck. My original concept was to gor for a xpg triple on the bar and helmet. Both 35mm and running boost drivers from a 7.4v battery. Thats getting expensive but would kick ass.
    Its a tricky one...now i see why Ayup split their lights into a bar and helmet.

  20. #20
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    Quote Originally Posted by mercman
    yep thats pretty much was i was asking. My current setup is a 35mm triple XPG and at low power 700mah its as bright as a magicshine. On high, well there's not much brighter that i have seen. Now im looking at refining the beam patterns to get a bit more throw.
    Swap out the XPGs for XPEs.
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  21. #21
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    xpg vs xpe

    so why xpe over xpg. From what i have read the xpe has a better spot but the colour is more yellow. I like the colour of the xpg. Is there an equivilent colour in the xpe.
    I read the posting on here about the regina optics. Troutie's test images are awesome. Its sold me on the whole reflector as opposed to optic.
    So now im thinking a single xpe or xpg 20mm with regina reflector and a bflex buck driver with a 7.4v battery to avoid the additional concerns about heatsinking the driver. this gives me huge runtime. I could do a 24hour race on one set of batterys.

    Im curious. What reflector would people recommend for a wide beam on the bar. something to compliment the regina on the helmet. Or would it be best to stick with regina's all round.

    Im getting excited. Now to redesign the housing....

  22. #22
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    I currently run a 35mm triple XPG helmet light with the narrow optic and the same light on the bar, but with the medium 35mm optic. Each light contains a buck driver, because of the efficiency and lack of heat sinking, and are powered by 4-cell Sanyo 18650 2600mah battery packs. 95% of the time I run them at 500ma drive current because that is plenty of light and it's an extremely efficient setup. They are as bright as a pair of magicshines, but I get a 7 hour runtime with less total system weight than a magicshine. 7 hours will typically get me all the way though the dark hours at most 24hour races. I also still have the option of switching up to high in the rare cases where I need more lights or switching them to even lower current for longer runtimes. If you want more details on the lights, look at my light history thread in the footer of my posts.

    I mention this, because I played with switching to a configuration similar to what you're thinking about. A single XPG on helmet with 20mm optic or reflector, and different combinations of single and double XPGs on the bar with 20mm optics with a little wider beam pattern. It was plenty enough light to ride with when solo, but I didn't think it was quite enough for riding in races or group rides with other riders and their typical light setups. Not quite bright enough to keep from being washed out by other lights. I also didn't like that I would be running the LEDs pretty hard all the time, that doesn't give good efficiency. Since you already have one triple XPG light, wouldn't it be easy to just add another light for a dual light setup? Maybe another light just like it, or something like a dual XPG light with 20mm optics for the helmet to give more throw.

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    I've decided

    MTB McGyver. Well thanks for your input. I've read some of your other threads about the comparasim between 35mm and 20mm. So its as i thought. 35mm is definately brighter than 20mm. So im going to go with my 35mm triple XPG and optics and do an extra one on the bar. This time though ill go with the maxflex driver so i can get some 7.4v batteries. Smaller and cheaper than the 14.8v batteries. Ive made this setup before and was quite happy with thte runtime.

    Can you give me some advise on optics. Are the cute optics the go or are there some better optics around.

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    For either the 20mm or 35mm, about how many lumens are they putting out with a 7.4V battery at 700mah? How about 1000mah? I am assuming the 700 is more efficient but the 1000 ultimately puts out more lumens.

    Can't wait until more of the L33.2MC are available.....

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    Hi Mercman, if you are going to a 35mm and using a maxflex it is a very small step to go to 39mm with seven leds (like the Troutie Seven up).

    When run at reduced current these provide the awesome efficiency.

    However - you'd probably want to go to a 4s battery.

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