Newbie led flash light help

Discussion in 'The Projects Forum' started by scubadank, Oct 27, 2008.

  1. scubadank

    Thread Starter New Member

    Oct 27, 2008
    3
    0
    Im trying to build an LED dive light, I am good with the mechanical side of making everything, but outside of knowing how to solder I really have no clue about circuitry. Hopefully some one out there can help spell this out for me.

    I was looking at using at least 3, possibly 5, of the Endor Rebel, tri-emitter led that produce 435 lumens @700mA
    . I was thinking of powering these with a 700mA buckpuck.

    Can I connect the LEDs in parrallel with this buck puck, will it keep up with the higher current draw of the total LEDs?

    I would think if I connected the LEDs in serial the voltage requirement would get extrodinary, the forward voltage of each led is 9.45volts, so inorder to connect 5 together they would need to have a 47.25 volt power source right? so that is out of the question.

    I was thinking of using a 14.4 volt, 10000 mAh Nimh battery pack. Unless I am completely wrong, which I most likely am, the LEDs should draw 3500 mA right, so it should give me on the better side of 2.5 hours burn time right??

    The battery pack is going to be in a seperate cannister so it will be over 18in away from the buck puck (in the light head) so I need to use a 50v capacitor across the input voltage terminals in front of the buck puck, and I was going to use a push button on/ off switch right after the battery.

    Does any of this seem crazy, it probably is...

    thanks in advance for helping a newbie out.

    -Al
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The buckpuck can output a voltage up to 32 Volts thus you can connect 3 of your leds in series and then in series with an appropriate resistor (10.5 ohms, 2 Watts) to limit the current to 350mA. Then connect the other 2 leds also in series and then in series with an appropriate resistor (37.5 ohms, 5 watts) to limit the current to 350mA. Thus the total current in your network will be 700mA and the battery will last longer than if you connected all the leds in parallel.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Al,
    Dive lights are pricey for a reason; they're tested and certified for a pressure depth.

    For your own safety, and that of your dive partner, I suggest that you only use certified gear on your dives.

    If there were even the smallest leak in the flashlight housing, the water would find it's way in, and the light would cease working immediately. The batteries and LEDs would be crushed by the pressure. You would then be at depth, in blackness.

    Diving is risky enough. This isn't something that you should experiment with unless you have the means to get it certified.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The LED says "max 350mA continuous". It also mentions 700mA but maybe not continuously.
     
  5. scubadank

    Thread Starter New Member

    Oct 27, 2008
    3
    0
    mil3, thats exactly what I was looking for, thanks for the help that sounds like a good plan.

    SgtWookie: thanks for the concern, but Im defiantly more confident in my machining than alot of the work out there by certified companies, not to mention im already riding on my homebrewed rebreather too

    As far as the max 350mA continuous, I figured that since the aluminum light head is only going to be used when surrounded by near freezing great lakes water, and that the LED specs say there is a 50,000 hour life at 700 mA, which is longer than I think this light will be in use

    thanks again Al
     
  6. scubadank

    Thread Starter New Member

    Oct 27, 2008
    3
    0
    one more question for mik3, if i do your plan the buck puck says "DC input voltage from 5V to 32V. (The input voltage must be at least 2 volts higher than the forward voltage drop of all series connected LEDs.)" does that mean I wouldn't be able to use the 14.4 volt battery?

    thanks again
    -Al
     
  7. antidote

    New Member

    Nov 12, 2008
    2
    0
    Hey guys,
    this may seem silly, but I'm not too familiar with the inner workings of BuckPuck and trying to put an LED together. I have the 1000mA version. My question is, is there any chance you'd get electrocuted with a 12V battery hooked up to it? ... I know a 1000mA to the heart can cause it to stop, but will a 1000mA BuckPuck driver electrocute you?
    thanks!
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    12V might cause a current of 1mA in you if you are wet with salt water. It might tingle.
    120V might kill you because then the current will be 10 times higher.
     
  9. antidote

    New Member

    Nov 12, 2008
    2
    0
    thanks for the reply Audioguru! so to clarify, the fact the BuckPuck says 1000mA on it doesn't mean it can drive it through your body? it's 1000mA constant through the LED?
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Ohm's Law tells you how much current flows in a resistance with a certain voltage.
    A car battery can produce a current of 400A in a cold starter motor but if you put your hands across the 12V terminals then the current will be extremely low because you are not made of very low resistance copper.
     
  11. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    The BuckPucks are switching regulators, nothing more.
    You might consider making your own regulator, which could be tailored to your exact load AND be made with a dimmer option (step or gradual) to give a longer runtime (after all, you probably don't need full power all the time).
     
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