LED lighting

[skylark]

I did some testing on Cree 1W Warm White Star LED's to see if they would work within the range of a 12V lead acid battery system powered by a solar cell with a charge controller.  The goal was to run 4 Star LEDs in series using no voltage regulator.

12V lead acid battery voltage range:

Min V: 50% discharge at 67F: 12.61V
12.61V / 4 LEDs = 3.15 V across each LED

Max V: Maximum recommended charging rate: 14.4V
14.4V / 4 LEDs = 3.6V across each LED

Note that there may be an inrush current when the LEDs are switched on, this does not take inrush current into account.

Voltage range for each LED: 3.15V - 3.60V

I did some testing using 2 LEDs in series, setting the Voltage using a V regulator, and measuring A. The single LED V is one half of the measured V. Note that amps should be the same for a single LED.

Voltage - single LED V - measured A
7.35V - 3.68V - 0.43A
7.23V - 3.61V - 0.40A
7.21V - 3.60V - 0.38A
7.10V - 3.55V - 0.35A
7.03V - 3.52V - 0.34A
6.84V - 3.42V - 0.30A light still bright
6.71V - 3.36V - 0.26A
6.48V - 3.24V - 0.21A
6.32V - 3.16V - 0.19A
6.24V - 3.12V - 0.17A light still relatively bright
6.04V - 3.02V - 0.12A light still usable though not as bright
5.72V - 2.86V - 0.06A
5.41V - 2.70V - 0.03A
5.18V - 2.59V - 0.01A
4.94V - 2.47V - 0.00A light appears, very dim

At the battery system max V, 3.6V across one LED, the measured current is 0.38A, which is higher than specified at 0.35A. Brightness is very bright.

At the battery system min V, 3.15V across one LED, the measured current is 0.19A, and brightness is satisfactory.

Ideally, at battery system max 14.4V (3.6V drop per LED with 4 LEDs in series) current should be the rated current (0.35A), which would indicate a resistance of 3.6V / 0.35A = 10.3 ohms.

A four LED in series system shows 0.38A at 3.6V, or a resistance of 3.6V / 0.38A = 9.5 ohms.

Adding a 1 ohm resistor in series would reduce that amperage at battery system max to just under the rated 0.35A. 3.6V / 10.5 ohms = 0.34A

It might provide some protection against inrush current when switched on.

It would diminish the amperage at the battery system min as follows:
3.15V / 10.5 ohms = 0.30A

At 0.30A the light was still bright.

Each LED requires a 1 ohm resistor, so for four LEDs, 4 ohms is required.

So with a 12V lead acid battery system powered by a solar panel and controller, I would recommend using 4 Cree 1W Warm White Star LEDs in series with a 4 ohm resistor, 1W or better, in series. NO REGULATOR IS NEEDED.

If there is an alternator on the system, it is possible that voltage spikes may occur.  This method may not be appropriate on alternator powered systems.

Here is a source for 1W warm white LEDs for a buck apiece:

http://www.satisled.com/1w-high-power-led-warm-white-star-emitter-8090lm_p119.html

[skylark]

I did a similar calculation for 5mm warm white LEDs:

12V lead acid battery voltage range:

Min: 50% discharge at 67F: 12.61V
12.61V / 4 LEDs = 3.15 V across each LED

Max: Maximum recommended charging rate: 14.4V
14.4V / 4 LEDs = 3.6V across each LED

Note that there may be an inrush current when the LEDs are switched on, this does not take inrush current into account.

Voltage range for each LED: 3.15V - 3.60V

Ideally, at battery system max (3.6V per LED) current should be the rated current (40mA), which would indicate a resistance of 3.6V / 0.04A = 90 ohms.

An LED shows 0.043A at 3.55V, or a resistance of 3.55V / 0.043A = 82.6 ohms for one LED.

Adding a 10 ohm resistor in series would reduce that amperage at battery system max to just under the rated 0.040A. 3.6V / 92.6 ohms = 0.039A

It might provide some protection against inrush current when switched on.

It would diminish the amperage at the battery system min as follows:
3.15V / 92.6 ohms = 0.034A

At 0.034A the light was still bright.

Each LED requires a 10 ohm resistor, so a total of 40 ohms is required.

To run LEDs without a regulator on a solar powered lead acid battery system, add a 40 ohm resistor in series with 4 5mm warm white LEDs.

[skylark]

I made some cabin lights for my decked sailing canoe out of 5mm LEDs.











This project will use an incredibly high tech and innovative system of voltage regulation: I am using old batteries that previously were used for an electric bicycle and are pretty much worn out.  The batteries do not allow the voltage above about 12.8V.  So a series of 4 LEDs needs no regulation at all.  The batteries do not have the capacity that they used to have, but I am now pulling less than an amp where the electric bike used to pull close to 20 amps, maybe more on startup.

The LEDs are rated 3.0V to 3.4V.  Four in series would be rated at 13.2V.  I don't expect my old batteries to allow the voltage to rise above 13V, even under charge from the solar panel.
I got the LEDs for about $65 for 1000 pcs.  There are 20 LEDs in each of the arrays, so one array costs about $1.30 for LEDs, plus some scrap plexiglass, some solder and a couple of pieces of wire.

The 20 LED lights will pull about 0.1 amp, since each 4-series is rated for 20 ma and there are 5 four-series.  The 32 LED light will pull about 0.16 amp.  In practice, actual amperage changes quite a bit with voltage.  This has the happy situation that as battery voltage drops, amperage drops so the battery will last longer.  Yes, the light output drops but it is still usable even at lower voltages.

My battery system has a 10W solar panel with charge controller.  I never expect to add an alternator to the system, which means it is fairly sure that that there will never be voltage spikes.  I will be adding nav lights to this system, but probably not much else, it is just for lighting.  My radio, gps, flashlight and vhf will run off of AA alkaline batteries.

To get the equivalent of a 40W bulb, my guess is that you would need an array with 40 LEDs, which would cost $2.60 and would use about 0.2 amps.

The strategy with LEDs is to put the lights so they shine right where you need them, and have enough different lights so there is always one light that lights up exactly what you want it to.  That way you don't need to light all the lights, you can conserve power by lighting up that area you are using.  And if you want to light up the whole boat for some reason, you could do that too by turning them all on.



with flash, no light - batteries are up front, tied down under the boards

with flash, light on

without flash









Solar controller and positive buss bar



Negative buss bar and rats nest, needs to be cleaned up.

[CharlieJ]

Nice job Skylark

[CapnK]

Very cool, Paul. I've thought along the same lines (no pun intended), about using that see-through speaker wire where possible. It's plenty big enough for LED's, and though not tinned, you can visually inspect the actual wire. Plus it's cheap to carry some extra for 'if-needed'. Seeing what you've done helps me crystallize my own plans. Gracias & Grog! :)

PS - Nice job on the build, too.

[skylark]

I have some extra 5mm warm white LEDs, and might be willing to sell some pretty cheap.  I'm going to make a few more lights for my big boat (which will require a regulator of some kind), but I don't think I will use up all of the bulbs that I have.    Any SailFarers interested in experimenting with LEDs, PM me.