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  1. #1
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    xm-l minewt dual noob questions

    So I have a 1st gen nightrider minewt dual that has just been sitting for the last 3 years since I got a trinewt and the dual doesnt put out enough light to not dissapear in the trinewt beam. So I was thinking about swapping a couple xm-l leds in place of the stock leds.

    It looks like the physical size of the xm-l is the same as the factory one but im no electronics guru so im not sure if I can just un-solder the old one and resolder the xml in its place on the same board.

    I took some measurements with my multimeter at the tabs the led attach to the board and heres what I came up with:
    High: 3.3 volts and 2.17 amps
    Low: 3.14 volts and 1.95 amps

    I ran those numbers through an online calculator to figure out watts and I got:
    High: 7.161 watts
    Low: 6.123 watts

    I looked at the xm-l data sheet and it looks to be 100lm/watt so am I correct in assuming this will create ~700lm/ led so ~1400lm on high?

    My head hurts trying to figure out if this is feasable or not before I order 2 leds and ruin a set of functional lights. Also I have a cheap solder gun I picked up from the hobby shop when I swapped my electric rc cars motor and some thin gauge lead free soldier. Will these work or do I need to factor in a better soldering set up?

    Ive been wanting to build a set of lights from scratch but that scares me so I figure this is a good place to start and not have to worry about battery, charger, circuit protection, and a decent housing. Besides the fact I think it would be funny for a light that only puts out ~250 (max) to put out 1400lm to match my riding buddys night rider pro 1400.

    Thanks ahead of time for dealing with my noobness.

  2. #2
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    Unfortunately, it's not quiet that easy. First, how did you take the current measurement? To get an accurate current measurement, you have to unsolder one of the wires and put the meter in-line. But niterider also uses PWM sometimes, so even that direct current measurement may not be totally accurate. There is no way that light is putting out over 2 amps, sorry!

    Niterider seems to use the Seoul Semiconductor P4 LED alot, so that is probably what's in your light. The absolute maximum rating for that LED is 1000mA. If your voltage measurement is correct, that would equal about 500mA.

    Swapping in an XM-L will get you more light and longer run times, but that swap is not so easy. Buying a bare XM-L and soldering to it is VERY tricky. Better to buy one already mounted to an MCPCB of the correct size and swap the whole PCB out.

    Some pictures would be helpfull as well.

  3. #3
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    It would be very cool if you managed to swap out the whole board the led is mounted on four an xm-l and also seaplane the reflector for a Regina. I think it should all fit in there. Search hard on here lots of folks have successfully torn down and reassembled various niterider models.

  4. #4
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    Quote Originally Posted by G14it
    I took some measurements with my multimeter at the tabs the led attach to the board and heres what I came up with:

    High: 3.3 volts and 2.17 amps
    Low: 3.14 volts and 1.95 amps
    You correctly measured the emitters Forward Voltage (Vf).

    ...but if you stuck your multimeter probes on the powered-up emitter with your multi-meter switched to read amps, you essentially provided a dead short around the emitter. The emitter probably went dark when you did this (ask me how I know), and the current flowed through the multimeter instead. That was what you were reading.

    Instead of cutting the emitter circuitry, you could just take a reading the current flow between the battery and the lights circuitry; this should give you enough information to estimate the emitter's actual draw. Just estimate a reasonable driver efficiency. 80%? 85%?

    i.e. A current reading of 1.0 Amps * 0.85 = 0.85 Amps, means you would have 0.85 flowing to emitter.

    Set your multimeter to read amps, and put your meter in series with either the positive or negative power lines coming from the battery to the light. Polarity doesn't matter.

    (+)-----------x Red Multi meter Probe ----{Meter} ---- Black probe x------------(+) battery
    Light {
    (-)-----------------------------------------------------------------------------------------------------(-) battery

  5. #5
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    Unfortunately, that will not work. Because the battery voltage is different than that of the LED, the current coming off the battery will also be different than the current going through the LED. The battery is probably 7.4 volts if it's lithium, and the LED is getting something like 3.3V, so the driver is stepping down the voltage and providing constant current to the LED. In this case, the current from the battery will be less than half what the LED is seeing. The only way to accurately get the current is directly at the LED. And even that sometimes doesn't work. If the driver is using PWM, the current is pulsed, and the meter gives false readings.

    I am in the process of replacing the Seoul P4 LED with an XM-L in a Minewt 250 cordless light. I started a thread on it, take a look at it, it may help your conversion as well:

    Niterider Minewt 250 cordless - deconstructed

    Quote Originally Posted by P220C
    You correctly measured the emitters Forward Voltage (Vf).

    ...but if you stuck your multimeter probes on the powered-up emitter with your multi-meter switched to read amps, you essentially provided a dead short around the emitter. The emitter probably went dark when you did this (ask me how I know), and the current flowed through the multimeter instead. That was what you were reading.

    Instead of cutting the emitter circuitry, you could just take a reading the current flow between the battery and the lights circuitry; this should give you enough information to estimate the emitter's actual draw. Just estimate a reasonable driver efficiency. 80%? 85%?

    i.e. A current reading of 1.0 Amps * 0.85 = 0.85 Amps, means you would have 0.85 flowing to emitter.

    Set your multimeter to read amps, and put your meter in series with either the positive or negative power lines coming from the battery to the light. Polarity doesn't matter.

    (+)-----------x Red Multi meter Probe ----{Meter} ---- Black probe x------------(+) battery
    Light {
    (-)-----------------------------------------------------------------------------------------------------(-) battery

  6. #6
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    Ok, so determine the amps at 7.4 V, convert that to watts, then factor in 85% driver efficiency, and then convert back to amps at the Vf of 3.3 V.

    I'd bet a dollar to a doughnut using the estimated 80-85% of the wattage from the battery to driver would be pretty damn close to the actual wattage flowing between the driver and emitter.

    At this phase of the project, considering that the OP is trying to decide if he wants to begin surgery on the light or not, I'd want to avoid cutting wires that are hard to reconnect.

    Later Edit: Be sure to take a voltage reading of the battery pack under the respective loads to ensure your wattage figures are correct. If the pack is fully charged and new, you will have a few minutes of 8.4V. It would be best to wait until this levels out around 8.0 or so, which is the flattest portion of the discharge curve.
    Last edited by P220C; 03-25-2011 at 11:01 AM.

  7. #7
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    Well I think I just killed one of the emiters (small puff of smoke and it wont turn on now) so at this point I figure why not just use the housings to make a sneaky set of stoopid bright lights. So I guess at this point I will just start saving for all the parts needed to build it including battery. What do you guys think would be the "best" parts list to build a set of 20mm diameter dual head lights in parralel? I know I need cells, tabs to connect cells, some good wire, but whats the deal with drivers? And how do I know what parts play nice with other parts? I looked at the spec sheets of emiters but I cant figure out what all of it really means. I normally would just dive right into building something but it the parts for these things arent cheap so I want to get a little educated on this before I spend any money.

    I know it would be alot of work but I think if there was a sticky explaining what all the info on a spec sheet means along with the math involved to build a light there would be alot more people building their own lights and more people getting into night riding because the $500+ for a good set of lights is a bit hard to justify for most.

  8. #8
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    If more people would do some more reading on this forum and some less questioning, there would also be a lot more builds to see. Educate yourself from other threads to find out what you need. Placing a question and expecting to get served on a silver plate to build a perfect light is a bit ridicilous. You've got XR-E, XP-E, XP-G, XM-L, MC-E emitters from Cree that are most popular, you also have Luxeon Rebel, SSC P4 and P7 used in some other builds. Most popular drivers are from Taskled, some also use cheap DX and KD, maybe Teapot or DerWichtel drivers. You've got lots of choices you just need to figure out what you want. With so many different build threads including step by step photo material and excellent beamshots, you really shouldn't be asking too many questions.

  9. #9
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    Oh no! You let the magic smoke out: the stuff that make emitters glow.

    Welp, now your committed to the project. It's kind of like burning the boats during a raid; there's no turning about now.

    I'm looking forward to reading about this build as you progress.

  10. #10
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    So im thinking I will use xm-l's on a 20mm star, a taskled LFlex driver, and for the battery pack I was thinking s3p1 out of 2800mAh 18650 cells but im not sure how to calculate runtime so I dont really know if I need to do a s3p2. I want at least 2 hours out of a pack.

    Toaster79: Im not expecting anybody to plan it for me and I would gladly search and do my own math if I knew the formulas and what the different specs mean. Thats really what im trying to accomplish with building a light for my bike. If it works out decently I dont plan on stopping at bike lights. I know I could just copy a build but thats not learning now is it.

    What I was asking for a sticky for is the different formulas and what some of the symbols used for the spec sheets are since my keyboard doesnt have those symbols so I cant just google it to find out.

  11. #11
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    http://en.wikipedia.org/wiki/Ohm%27s_law

    LFlex is designed to run 1 XM-L per li-ion cell in series. Add more cells in parallel to increase runtime.

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