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Thread: Underwater 12v XPH70 Build for Boat

  1. #1
    Join Date
    Apr 2021

    Default Underwater 12v XPH70 Build for Boat

    Idea is to build an underwater light for a boat.

    Basically I want to create my own version of this: is external)

    Example of someone trying to do this but doesnt look like they accounted for heat, or the latest LED tech:

    • Voltage Source = 12v battery (assuming volt has a range of 12v with engine off to 14v while engine running)
    • Battery Source: Interstate Batteries | 24M-XHD

    LED Option 1: XPH70.2 12v
    Cree XHP70.2 P2 5700K on DTP MCPCB (
    • High lm/w option with lower heat than 6v version due to lower current draw
    • BUT, I cant figure out a driver to use. If the driver reduces the source volts, then the LED wont work while the engine is off, right?
    • 17mm MTN-MAXlp HP 1A-5.5A Low-Profile Buck Driver - 5V-18V (
    • Is there a cheaper driver anyone could suggest?
    • The datasheet says 1050mA preferred current, and 2400mA max current. But I've seen other threads where people run these much higher. Is it ok to aim for 2400mA or should I aim lower? (assuming good heat management)

    LED Option 2: XPH70 6v
    Cree XHP70 N4 1A on 16mm / 20mm DTP MCPCB (

    Option 1: Water cooled
    • LED covered with clear epoxy
    • LED on top of aluminum heatsink, attached to the outside of the boat, in the water
    • Hole cut in boat for wires

    Option 2: Air cooled
    • LED against inside boat wall
    • Heatsink behind LED, air cooled

    Option 3:
    • Boats have a 1" diameter drain plug in the back underwater
    • Could leverage that as an attachment location that doesn't require drilling holes

    Thermal Heatsink Calculations:
    - Lifetime Case Temp est: 100C
    - Ambient temp ~ 30C
    - Vf1 =12.6v | Vf2 = 6v
    - If1 = 1 – 2.5A | If2 = 2 – 5A
    - Efficiency ~ 70%
    *HeatSink Thermal Resistance for 12v&6v is ~ 3-7.5 C / W
    or 9 – 23 watts needing to be dissipated*
    dT = Case Temp – Ambient Temp
    Pe(W) = Vf * If
    Pd = W * Efficiency
    Rth = dT / Pd

    - Can I use the 12v Led with 12v source? If so, what driver should I be using?
    - What driver should I use if I cant use 12v and have to use 6v LED?
    - Any ideas for water proofing an LED?
    - Any suggestions for very flat heatsinks, so it be as flat against the boat wall as possible?

    Thank you!
    Last edited by efine; 04-13-2021 at 02:16 PM.

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