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## mb82

129 posts

Master Geek

Topic # 207280 16-Dec-2016 22:50

Making a battery powered navigation light. Don't want to use 12v due to size.

Basically my thought is if I can buy a 2xaa battery powered led torch which is stupid bright it should not be too hard. If I had half that light in each direction (back to back) on 2xaa cells it would be perfect.

Looking at running on 3v (2 x aa cells) or 6v (4 x aa cells). Most led's throw light in one direction which means the light is somewhat wasted as it is not in the direction I need it in (360 degrees pointing outward from the center).

Currently thinking of this: (pic below) although I suspect it is really built for 12v and they just advertise it as 6v.

How much heat would this cause?

It is apparently 0.8w how do I work out how long it will last on 4 x 1.2v 1900mah batteries?

Any better ideas?

## elpenguino

750 posts

Ultimate Geek

assuming perfect 6V supply, figure out the current draw:

P = IV so 0.8 = 6I

0.8 / 6 = 0.133 Amps

Now from battery capacity:

1900 / 133 = 14.2 hours

But 4 batteries makes 4.8 volts and you need 6 volts so add another battery :-)

Of course, these are idealised figures so you would get somewhat less, but there's the size of the ballpark right there.

## mb82

129 posts

Master Geek

That was how I 'thought' it was calculated but I wasn't sure. Cannot have more then 4xAA cells due to space limitations. It seems there are plenty of bright 1xaa and 2xaa torches which only cost \$1 - \$2. Nobody seems to make the bulbs in the picture above for 3 volts. Maybe I have to build one myself out of a few led chips, but where to start? do I need a driver?

## richms

21839 posts

Uber Geek

Trusted
Subscriber

The forward voltage of white LEDs is around 3v, to get appreciable current thru them you need more than 3v. You will need something to step the voltage up if you want to keep it off 2 cells. Plenty of little boards to take 3v up to a 5v usb supply available, and that would probably be fine for a 6v led as they will not have more than one in series so it should still light down to 3ishv, but will need close to 6 to get its proper brightness.

Richard rich.ms

## frankv

2647 posts

Uber Geek

A couple of thoughts...

You can buy quite cheap 360 degree mirror 'lenses' for e.g. cellphones to take 360 degree photos. You could probably use one of those with a single lightsource (e.g. flashlight)?

It would probably be worth adding a Fresnel or similar lens to diffuse the light from the 4 LEDs into more uniform coverage.

Rather than AA batteries, I'd get a USB powerbank... much cheaper in the long run. Add a step-up voltage converter if needed for 6 or 12V or whatever.

A major issue with navigation lights is (I assume) reliability and waterproofness. What are you going to do if it fails? Perhaps you should set up two separate nav lights with separate batteries, etc?

Is this a nav light for a boat? Or a fixed nav light to be on shore? What are the legal ramifications?

## mb82

129 posts

Master Geek

I am using a solar garden light for casing. Waterproofing is easy to deal with, a garden light to begin with is somewhat rain proof by design. casing has dispersing cylinder with cone shaped reflector at the bottom but I feel like led's pointing in the right direction will be allot more efficient, my stupid bright torch shining into the solar light casing is no comparison to the 100+m beam distance it reaches with normal use.

Will look into usb power bank, was trying to avoid due to my mis-trust of cheap Chinese lithium batteries.

Legally only need a torch dinghy/kayak, but 360 degree light is safer as torch only points in one direction, and a pain holding it all the time. If it fails I will have a backup torch.

I think these look like the solution:

0.5w straw hat led.

I have a couple from single aa torches, they are mounted to boards with 0.8ohm limiting resistor and some chip which I assume steps up the voltage.

I am thinking 3 - 4 of these 0.5w straw hat led's. I understand current limiting resistors and the difference between parallel and series wiring. Just need to know what I should use to step up the voltage? The smaller and more compact the better

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