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My dad has a 100 year old sailing yacht that he's spent the last 37 years restoring and is almost finished. One of the last few things is the navigation lamps; these would normally use kerosene, but we're keen to convert them to LED. We also don't want unsightly wiring, or to have to pierce the deck for cabling, so think a LiPo battery should work.

I'm a (the horror!) Mechanical Engineering grad so electronics really aren't my strength, so I thought I'd better check:

The 12v bulbs we need to use (to give us the required visibility range) are 50 LED ones with a 3.5 watt draw. I think I can use a 4s 3300mAh 14.8v LiPo battery pack (this will fit within the size constraints of the nav lamp), giving approx 11 hours of duration:

3.3mAh x 12v = 39.6Wh / 3.5W = 11.31 hrs.

But this assumes I can use a Buck converter to reduce the voltage from 14.8 to 12v. As I said I'm no expert, but from what I can see it looks like there's a minimum power output required from a buck that the bulb doesn't meet. Is this correct, or can I actually use a Buck? (If it's as easy as that, then it would all fit happily in the nav lamp). Whatever the solution is, it needs to be reliable (simple?), work with the chosen bulb and give at least 10 hours continuous duration.

I'd value your thoughts.

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  • \$\begingroup\$ 3.3mAh x 12v <-- you mean "3.3 Ah x 12 V". Also, never have the units and the value without a "space" separator. I have 4 cats and not 4cats. Please link to the data sheet of the specific LED you are considering. You can use a buck-boost if you want and run the cells all the way down to their lower limit (assuming they have protection circuits built-in). \$\endgroup\$
    – Andy aka
    Commented Dec 28, 2022 at 20:03
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    \$\begingroup\$ Aesthetics aside, please also take into account that navigation lights might need to be certified (depending on your sailing area). Also take into account that retrofitted white LEDs might not work very well through a red/green filter used in port/starboard side lights. \$\endgroup\$
    – StarCat
    Commented Dec 28, 2022 at 20:38
  • \$\begingroup\$ Andy aka: you are quite correct, and I stand corrected. Unfortunately the data sheets are unavailable (or at least not available through the chandler's website). StarCat: we were intending using the appropriate colour of LED for each colour lens - certification is not required in this case; for the size of vessel, port/starboard lights have to be visible up to 2 nm away - we're using bulbs for the next higher rating of 5 nm, which should give plenty of wiggle room (regardless, anything would be better than the paltry light from a small kerosene lamp!) \$\endgroup\$
    – Jimbo100
    Commented Dec 29, 2022 at 1:02
  • \$\begingroup\$ I would expect 3W lamps to have internal buck converters. can you link to actual products? \$\endgroup\$
    – Jasen Слава Україні
    Commented Dec 29, 2022 at 12:24

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If the LED lamps are designed for use on the usual automotive or marine "12 volt" system, they should be designed to accept up to 14.5 volts, as that is the normal system voltage when the engine is running and the alternator is charging.

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    \$\begingroup\$ Nominal 14.8V lipo cells are something like 16.8 (4.2V/cell, times 4 cells) when they're fully charged. I think that's a bit high, unless that usage was anticipated. \$\endgroup\$
    – TimWescott
    Commented Dec 28, 2022 at 20:19
  • \$\begingroup\$ Most marine type LEDs I'm familiar with have wide voltage range (usually up to 30V). \$\endgroup\$
    – StarCat
    Commented Dec 28, 2022 at 20:43
  • \$\begingroup\$ The bulb is listed as 12/24 volt, and is a direct replacement for a 25w bulb. Like I said, definitely not comfortable in the electrical/electronic space, so before forking out almost £100 (per lamp) for battery and bulb, I'd like some sort of confirmation that it will work, and give the duration we're looking for. \$\endgroup\$
    – Jimbo100
    Commented Dec 29, 2022 at 0:44
  • \$\begingroup\$ @Jimbo100 If it works on 12 V and on 24 V without any modifications (like a switch or jumper for what input voltage you're using), I would be very surprised if it didn't also work on any voltage between 12 and 24 V. \$\endgroup\$
    – Hearth
    Commented Dec 29, 2022 at 15:48

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