Underwater XPH70 LED for a boat

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Underwater XPH70 LED for a boat

Idea is to build an underwater light for a boat.

Basically I want to create my own version of this:

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 XH P70.2 P2 5700K on DTP MCPCB (mtnelectronics.com)
-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 (mtnelectronics.com)
-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 (mtnelectronics.com)
-I could use a buck driver but then I have a lot more heat generation
-$5.21 26mm 4500mA 1-Mode LED Driver Circuit Board for Flashlight DIY – for Cree XHP70 / 6-15V at FastTech – Free Shipping
-Data sheet says 2100mA preferred current, and 4800mA max current. Which one should I aim for?
-This forum has a graph showing amps/lm & volts Cree XHP70 up to 4022 Lumens and XHP50 up to 2546 lumens – Multi-die leds. | BudgetLightForum.com

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!

Edited by: efine on 04/13/2021 - 14:04
mountainair26's picture
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Location: Louisiana, USA

Cool project and idea. Welcome to BLF.
I’m no expert, but I would think you definitely need a driver unless your battery is the weakest there is or it will instantly blow the led. The xhp70.2 vf is less than 12v and the current is way less than what a lead acid battery puts out. I think some others on the forum recommend these drivers and other Led supply drivers, but I’m not sure if they meet your application:


This seller in Canada seems to have drivers that might fit your needs, maybe message him through ebay: https://www.ebay.com/usr/onstatetech

Here’s some helpful data on what current and vf to expect with XHP70.2, it’s 6v but double for 12v results:


You can also search for a driver used in 12v off-road lights on the forum, or google “12v DC led driver”. I would imagine digikey or other electronics suppliers in the US have something that meets your needs if you search. Without knowing your location or how fast you need it, I know there are thousands on Ebay but many coming from china. Post your build pictures and project as it comes along, hopefully someone more knowledgeable than me chimes in. good luck.

buck91's picture
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Location: Michigan

If you go with a in-the-water mount (aka, water cooled) I don’t think heat would be any factor at all so long as there is a reasonable thermal path from the LED to the water. I’d go with a buck configuration.

Last seen: 2 hours 19 min ago
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Location: charleston wv

We camped on an island off the coast of florida and the next morning when all the fishermen were going out on their boats they all had lights like that drain plug light. It was bad ass for sure. I plan on just buying a cheap amazon green fish attractor and hanging it off my kayak for night runs.

Last seen: 4 months 4 weeks ago
Joined: 04/13/2021 - 12:11
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Instead of buying an expensive retail solution or having to engineer my own light, I found out about Chip-On-Board (COB LEDs). No Drivers needed. The board is aluminum and therefore waterproof and rust proof. The lights are covered in epoxy so also waterproof.

I found one that claims 3500-7000lm for $10 and is waterproof and rust proof by design. Used just two bolts to mount it on the back of my engine mount underwater, no holes in the hull, and ran two wires to my existing light switches.

Brighter than anything else on the market for boats and a fraction of the price. It’s been on the boat the entire 2021 season with no issues so far.


The manufacturer claims 12v minimum, +13watt requiring a heatsink with a 14v max.
My boat runs ~12.6v with the engine off, and >16v while running. But since the light is underwater it seems to have enough cooling. Probably killing the longevity of the light but for $10 it’s still holding up well.

I havent tested the exact lumens but it’s bright enough to light up the entire back of the boat and wrap half way around the 16’ bowrider. A second one isnt necessary at all.

I added pictures on this thread:

I found one manufacturer that produces underwater boat lights at same or brighter lumens. But they dont sell directly and it seems like a marine shop would have to make a special order: https://www.oceanled.com/leisure/below-water/
A quick google search shows their prices from mid 100s to 1000s:
Does anyone actually buy these that doesnt have a huge enough yacht where money isnt even a consideration?

Rdubya18's picture
Last seen: 3 days 15 hours ago
Joined: 10/28/2018 - 18:42
Posts: 633
Location: Ohio

That’s really cool ! If I still had a boat , I would have to do that Thumbs Up