MC-E Question for Dynohub- Mtbr.com
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  1. #1
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    MC-E Question for Dynohub

    I'm something of a noob in this area and am trying to decide how to put my next light together. I'm now running two Q5s in series powered by a Schmidt dynohub and it does a pretty good job but the tinkerer in me can't leave well enough alone! My application is road riding but it's pretty obvious that you mtb guys have this light stuff nailed so maybe you can help.

    I've hooked up a series MC-E to the hub and recorded the current draw from 0 to 42 mph. Here are the data points:

    mph mA
    5.3 1
    7.2 23
    10 100
    16 256
    20 339
    25 435
    30 473
    36 497
    42 514

    Obviously, the curve flattens at the top and it won't get much above 500mA. My question is whether this means that my setup is doing a good job of extracting most of the potential of the MC-E. According to the datasheet, each individual die should be pulling a half amp or more. I'm deficient in LED theory so I don't know if this means that four in series should be pulling more like a total of 2 amps or if the 500mA that passes through the series of four dies lights up each die to the same extent that it would if it were a single die through which 500ma were passing.

    I also surmise that 2s2p might make more sense in that the MC-E would reach maximum illumination at a slower speed. I haven't generated the data on this yet - am I correct that this should be true? And if so, will the maximum lumens turn out to be less than four dies in series?

    Any wisdom will be appreciated!

    Thanks!

  2. #2
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    Yes salty the dyno puts out 500mA once up to speed. This is for 1,2,3,4,more leds. On a decent cree this is around 150lm per led. An MC-E is 4 leds in one, so if wired in series you will get ~600lm.
    If 2S2P then the 500mA is shared between 2 leds, 90lm each, around 360 total... so efficiency is a little better... but not much brighter than your current light.

    Having fewer LEDs means more light at lower speeds(see pilom.com for charts). I think three is the sweet spot for a roadie, plenty of light and drag is not huge (10W), loving my new XP-E triple.

  3. #3
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    Thanks for the reply, znomit. Very helpful info, indeed! I'm going to go ahead and finalize the four-in-series and give it a try. I'm not too concerned that it doesn't begin to light until 5mph because I have a battery backup light to use on the slow climbs. With the exception of serious uphill stuff, my guess is that it will be adequately bright for the speed.

    I've tried the Boom SS and Eva D and it looks as if the latter has a better hotspot and more throw so that's the one I'll use unless someone has a better idea.

    Your suggestion that three-in-series may be the sweet spot is a good hint. That will be my next project, perhaps with a mix of optics to get the spill and throw just right. Can't have too many lights, eh?

  4. #4
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    Might this approach have some merit?:

    An MC-E could be wired with two dies in parallel and this pair in series with the other two dies, both in series. You might call it "1s1s2p." Would the parallel pair light up sooner than the two series dies, while ending up with what is otherwise equivalent to a three LED circuit?

  5. #5
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    Quote Originally Posted by saltytri
    An MC-E could be wired with two dies in parallel and this pair in series with the other two dies, both in series. You might call it "1s1s2p." Would the parallel pair light up sooner than the two series dies, while ending up with what is otherwise equivalent to a three LED circuit?
    Yes salty, that will be much like a 3 LED load, you won't notice the parallel dies lighting earlier but the two dies in series will be about twice as bright as the other two, so you can put them at the top of the beam to give more throw, or you can have them diagonal and mount the led at 45 degrees so the beam isn't as wide.


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