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Old 13-03-2008, 11:26   #1
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12v LED cabin lights

I bought a bayonet-style (two contacts) LED cluster from Pep Boys just to see the quality of light it would provide in the cabin. However, for some reason, I cannot get it to light in any of the sockets. It's the correct stem for the lights. Are these auto lights wired in some way that would keep them from working in the fixtures?
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Old 13-03-2008, 12:03   #2
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Try connecting a battery to it, just to see if it works.
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Old 13-03-2008, 12:16   #3
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Polarity of your wiring may be reversed for that cluster.
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Old 13-03-2008, 12:37   #4
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ah, polarity! of course, that must be it. I'll get back on that.
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Old 17-03-2008, 19:33   #5
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i buy a lot of boat gear (LED's, muffin fans, magnets etc) from American Science and Surplus. Some LEDs need current limiting resistors as 12 volts will blow the diode. and then they won't be 'light emitting diodes.' here's the info from their catalog:
see their latest info re LEDs:
LEDS BY THE DOZEN

Light emitting diodes. Solid state devices that provide the ubiquitous power and indicator lights on your electronic gadgetry. Unlike lamps, there are no filaments that glow. Rather, some two volts of DC power at a miniscule 10 to 20 milliamps of current get the chemistry excited, and they just plain emit. Emit is a good word, too, as they don't really cast light, but glow brightly. We have a nice assortment of 3 and 5 MM diameter sizes in red, green, orange, and yellow. The longer lead is always positive, the shorter always negative, and you always need a current limiting resistor (about 500 to 1,000 ohms for 5 to 9 volt DC sources) to keep the current in the 10-20 MA range. If that's Greek to you you're either going to blow a lot of LED's or learn to change incandescent indicator lamps ! !

Their 6796 LED ASSORTMENT has 12 of them for a couple bucks BUT they ALL need current limiting resistors....
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Old 17-03-2008, 20:56   #6
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This seems a waste. To have 10V across the limiting resistor, as it means over 80% of the energy is dissipated in heat. 5 or 6 in series would reduce the current and then have some sort of limiting resistor for fine adjustment,
Robert
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Old 18-03-2008, 10:00   #7
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you are right of course. the huge waste of power is why most folk don't try to use LEDs for inside lighting. i just ordered a 7 LED camplite for the cockpit that runs for 12 hrs off 2 AA batteries. i am not sure i want to try hooking it up to a 12v source and blowing the diodes.
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Old 18-03-2008, 10:20   #8
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If an LED is hooked up backwards it won't draw any current. It only operates when the diode junction is forward biased.

Even with a series resistor, the amount of light produced for the amount of power used is considerably more than you can get from an incandescent bulb.

Steve B.
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Old 18-03-2008, 10:58   #9
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polarity was indeed the problem in my case. i feel like a bonehead, but less so now that i know that. thanks for the tip!
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Old 18-03-2008, 11:21   #10
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Using bias resistors is old hat and doesn't work all that well on a boat. The voltage varies to much. The best way is to use a current limiting regulator. The best led units on the market are rated for something like 10 to 30 volts or so because they have a regulator built in. If you are building your own then one larger regulator to handle all the led lighting circuits is enough.
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Old 19-03-2008, 00:15   #11
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Quote:
Originally Posted by senormechanico View Post
If an LED is hooked up backwards it won't draw any current. It only operates when the diode junction is forward biased.

Even with a series resistor, the amount of light produced for the amount of power used is considerably more than you can get from an incandescent bulb.

Steve B.
Ok I'm confused but admit to being a self-confessed dumbarse with things electrical.

I don't like running my motor so swapped out all the old lights in my boat for LED. As they didn't put out so much light I just added a couple of extra. All work well and I'm saving masses of amps or thought I was. But reading your post I'm now thinking "Am I?"

I also built a LED anchor light. I had one of those garden solar ones but it just didn't put out enough for me to be happy so my 'More power Tim!' side kicked in. I went to the local electrical shop and told them what I wanted to do and they gave me a pile of bits which included some resistors. I built one and when plugged in it lit up the entire bay and the one next door.

So back to the drawing board and ended up with a variable resistor (high chance of not using the right names warning), I can adjust it anyway. It now works great and does give everyone in the cockpit sunburn.

Boat is 12v and runs entirely off one big battery which is charged by a solar panel when on the marina and I get a little off the motor when it's going, which isn't that often. I sail heaps faster than I motor anyway.

So am I actually saving power or not, you've confused this simple chap
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Old 19-03-2008, 01:15   #12
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LED's are not voltage operating devices. They are current operating devices. That means the voltage used is of no importance. But the current is. So a resistor inline with an LED works by disapating some of the current, which is seen as heat. So no, you are not really saving all the battery power you could do if you used a regulator.
However, regulators are not the only important point to consider. And this is where the expense comes in to some of the better LED units out there. An LED will increase in it's light emission as the current increases. But so does the heat it produces. And as the heat increases, the life decreases. Some regulators simply provide as much current as possible without destroying the device instantly. But they do reduce the overall operating life time. An LED is capable of returning about 100,000hrs of service. But many of the cheaper units have that figure reduced to 10,000 hrs. Still along time, however, it means the possibility of one or two LEDs failing early is quite possible. So the the tricky expensive regulators are pulsing the current. Far to fast for us to see with our eyes, but the LED flickers. This works very simply. Lets say for ease of figures, an LED uses 1A of current in one second. (just a figure to explain remember) So if you turned the LED on for 10sec's, then you use 10A, OK? Now if you turned it on for 1sec and then off for 1sec, then the current used over 10sec's would be 5A. OK?
So now scale this down to the very small current of the LED and speed up the pulse to fractions of second and you can see that the turning of the LED on and off reduces the heat it produces, thus increasing the life. It means you have very bright outputs, but less heat.
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Old 19-03-2008, 01:32   #13
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Quote:
Originally Posted by DeepFrz View Post
Using bias resistors is old hat and doesn't work all that well on a boat. The voltage varies to much. The best way is to use a current limiting regulator. The best led units on the market are rated for something like 10 to 30 volts or so because they have a regulator built in. If you are building your own then one larger regulator to handle all the led lighting circuits is enough.
Actually if you are going to use one regulator for all of the boats lights then you need to use a fixed voltage regulator because as you turn circuits on and off the required current will vary. The best way one regulator would work was if each light fitting had the same number and type of leds in a string, to get greater output from a fitting then there would be more strings of leds in that fitting. This would allow each fitting to not have a current limiting resistor wasting power.
A fixed voltage reg could be used with a voltage that is slightly higher than required in conjunction with a small resistor. This would allow for some variance in individual leds.
A single reg has no redundency and if it dies all light circuits fail.
I would use a switch mode regulator for each fitting. These switch the 12v in brief pulses. This can improve the efficiency greatly.

Mike
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Old 19-03-2008, 09:09   #14
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I'm in the process of replacing about 12 fluorescent fixtures in our boat with LEDs. I'm using the current "state of the art" Luxeon Rebel LEDs, along with a regulator for each of the fixtures. They ain't cheap. Parts are about $60 a light. BUT, I'm using less than 50% of the current that the fluorescents were AND I'm getting about 2X as much light.

As noted above, you MUST well regulate the voltage and current for long life - and it needs to be done in each fixture - the recommendation is within 2' of wire of the LEDs. Here's some good info:

Luxeon LEDs - Luxeon Rebel Star

As I'm having the LEDs mounted in Asia (buy from Canada, have it shipped to Texas, ship to Thailand, have it shipped back to Texas) because the LEDs are so small (about 1.5mm x 3mm), I'm having them make me a star with 2 white LEDs and 1 red, to replace my light over my chart table.
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Old 19-03-2008, 09:43   #15
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GMac,

Yes you are saving significant amps.

Steve B.
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