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Thread: Learning to build a light

  1. #1

    Default Learning to build a light

    My light building experience to date, has been to put a Malkoff drop-in, in my 6P Surefire. I'd like to learn more, a little at a time. If I could put a couple things past the experts, and see where I'm at, it would help a lot. I'm hoping other beginners like me, will benefit from this type discussion as well. Once I can understand this, maybe I can begin to tackle the 'pills' and electronics that are available.

    Please tell me where my thinking is flawed. I know it can't be as easy as matching up voltages with modules.

    I have available to me,an inexpensive source for Xenon bulbs in 6V, 7.4V. I have also ordered a couple of the R2 modules from DX that have been brought up here a few times. I have several 6p hosts available, in the form of Surefire, Ultrafire 501, and Solarforce L2

    - I could put the 6V Xenon in with 2 CR123s - that should be the safe path. If I put a 17670 or 18650 in, will it go off like a flashbulb ? Or just be very bright for a short lifespan ?

    - I could put the 7.4V in with 2 CR123s and it would be dim, but would light. An 18650 would be ideal for max efficiency and life ?

    - I can put the R2 module in and with an 18650, it would be much brighter than the Xenon in any case (because it's LED ?). 2 CR123s would light it also, but not quite to best efficiency and brightness.

    JimInFL

  2. #2
    Flashaholic* R@ndom's Avatar
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    Default Re: Learning to build a light

    18650 to a 6 volt bulb = dim, 18650 to a 7.4 volt bulb = dimmer.

  3. #3

    Default Re: Learning to build a light

    yeah a 18650 is 3.7 volts I believe like most single cell Li-ion's are.

  4. #4
    *Flashaholic* Gunner12's Avatar
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    Default Re: Learning to build a light

    The harder you drive an incan, the shorter the life. Same with an LED unless you are comparing a non heatsinked one to a well heatsinked one.

    A single Li-ion battery is usually around 3.7v, or 4.2 fully charged. With an incan bulb, the lower the voltage, the lower the efficiency, the lower the tint, the lower the output, and the longer the life. A 6v bulb at 4.2v of a single fully charged Li-ion will be dimmer then with the 6v of 2 CR123s (actually, CR123s are higher then 3v fresh, check it yourself). 2 Li-ion will burn out the bulb (8.4v).

    With the 7.4v bulb, with a single 18650, you'll only be driving it at half the voltage that it was rated at, so it will be much dimmer. But it will run a lot longer before it burns out. 2 CR123s will also be dimmer then with 2 Li-ion batteries.

    With LEDs, it's different. Single die white LEDs like then Cree XR-E have an input voltage around 3.3-3.7v. Unless you are direct driving the LED (batteries connected directly to LED, sometimes through a resistor, no driver) voltage shouldn't do too much to the output because most LED lights have a circuit to regulate the voltage to the LED. The R2 drop-in (this one right?) has a buck driver, which means it lowers the voltage to what the LED needs. Output with a fresh 18650 should be similar to with 2 CR123s. But as the battery dies, the voltage could drop below the operational voltage of the driver, and the LED will be dimmer then with fresh batteries. Efficiency wise, the LED will be much more efficient then the incan, so you don't need to worry about that much. 2 CR123s will be less efficient then with 1 18650 because the driver has to lower from 6v to 3.5-3.7v (actual voltage depends on the individual LED) vs 4.2v to 3.5-3.7v. Boost circuits, like the ones in 1AA or 2 AA lights raise the voltage to what the LED needs.

    Read over the Welcome Mat. it could help you understand a bit more.

  5. #5

    Default Re: Learning to build a light

    Ahhh yes. First flaw in my thinking. For some reason I was thinking that the 18650 was like putting 2 CR123s in series. Need to completely rethink this.

    So a 3.7V Xenon should work well.

    How about the R2 led ? It says 3.7 - 18V. Should I assume it's going to be extremely dim on an 18650 ? Is this where I'd need to begin to understand the additional circuit boards and electronics, to take advantage of that type setup ?

    JimInFL

  6. #6

    Default Re: Learning to build a light

    Thanks Gunner12 - I was posting while you were replying so I missed it. Good info. Let me digest it a bit and do some more reading.

    JimInFL

  7. #7
    Flashaholic*
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    Default Re: Learning to build a light

    Quote Originally Posted by JimInFL View Post
    How about the R2 led ? It says 3.7 - 18V. Should I assume it's going to be extremely dim on an 18650 ? Is this where I'd need to begin to understand the additional circuit boards and electronics, to take advantage of that type setup ?
    I don't think an LED would tolerate that kind of variation of voltage, so the 3.7-18V is most likely what the driver circuitry can handle and it will pass the correct voltage to the R2 emitter. What this means is the R2 will most likely run about the same from any combination of batteries that output anything from 3.7V to 18V. i.e. there is a good chance that it will be just a bright from 1 x 18650 as it would be from 2 x 16340.
    So many lights, so little money (cause I spent it on lights). I'm not afraid of the dark, the dark is afraid of ME!

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