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Old 27-12-2011, 11:49   #1
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Question About LED Power Consumption

I am about to order some more G4 LED units to complete the conversion of my zillion G4 halogen light fixtures on board.

My DC system is 24 volts.

I am not a genius in electrickery, although I try to learn. Some things I have read seem to indicate that buck-driven LED units draw the same current no matter what the voltage is.

Is that true? And if it is true, then it would seem to be bad to be driving them with 24 volts -- double the wattage for the same light, compared to driving them with 12 volts -- is that really true?

If so, then it would seem that I might want to put a dropper in that circuit -- does anyone do that?
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Old 27-12-2011, 12:02   #2
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Re: Question About LED Power Consumption

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Originally Posted by Dockhead View Post
Some things I have read seem to indicate that buck-driven LED units draw the same current no matter what the voltage is.

Is that true?
No generally Buck converters are reasonably efficient at a wide range of voltages, so the current at 24v will be close to 1/2 the current at 12v
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Old 27-12-2011, 12:02   #3
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Re: Question About LED Power Consumption

LEDs are driven using current regulators, not voltage regulator. So the output of the regulator should be the same current, regardless of the input voltage. So long as your regulator can handle 24 volt (nominal) input then you are fine. They do not use any more power at 24 volts than at 12 volts.
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Old 27-12-2011, 15:26   #4
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Re: Question About LED Power Consumption

My understanding is that the typical LED fixture will operate between 8-30 volts DC without trouble. I have already utilized this fact in practice, and instead of hardwiring little locker lights all over the boat with some tiny gauged wire, I have put magnetic switches in a circuit with LED strips and a 9-volt battery. Open lid, lights go on. Close lid, lights go off. Cost: about $18.00 for the lights and wires per locker, and one 9V battery per year per locker. The battery will age below 8VDC before you likely use it up.

To my mind, this is the beauty of LEDs: You can have little occasional directional lighting like this EVERYWHERE, and you can have shaded or filtered LEDs or indirect strips for cabinets/lockers, or IR triggered, three-second "flash" circuits in red or blue to light up companionway steps...so you can see them without blowing your night vision.

Install away. Next to AIS, the maturation of natural and spot LEDs is a great thing for cruising.
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Old 27-12-2011, 16:56   #5
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Re: Question About LED Power Consumption

S/V, what brand of lighting are you using for these local battery driven lights with door switches, and where did you order them? I had the same idea, and wanted to implement. Maybe you customized them, and if so, what list of parts? Pictures?
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Old 27-12-2011, 18:58   #6
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Re: Question About LED Power Consumption

There are three types (more or less) of current regulation in LED bulbs and fixtures:

1) Series resistor -- typically used for cheap automotive applications. They work OK I guess, but the large voltage excursions in a boat can cause the LEDS to burn out prematurely.

2) Linear current regulator -- used in the Bebi LED units. These are pretty bulletproof if well designed (the Bebi ones are good), but they will waste a little power at higher voltages. The wasted power is usually inconsequential, at least compared to the power used by the incandescent bulb being replaced. This style of regulator puts out no radio-frequency interference.

2) Switching regulators -- these put out a constant current too, but also consume a fixed (almost) amount of power regardless of the input voltage. These are probably slightly more efficient than the linear regulators, may be designed for a wider voltage range, and may be more expensive. Some of these can put out a bit of R.F. Interference, so make sure this won't be a problem for you. There are several switching topologies (buck, boost, buck/boost, with many ways to implement), but any of these should do the job. Look at the input voltage range specifications.
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Old 27-12-2011, 20:21   #7
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Re: Question About LED Power Consumption

Sensibulbs aren't cheap, but they are very efficient, work between 8 and 30 or so volts, have great light spread, good light temperature and produce NO RFI.
I'm glad I bit the bullet. No financial interest, just a happy camper.

www.sailorssolutions.com
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Old 27-12-2011, 20:30   #8
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Re: Question About LED Power Consumption

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Originally Posted by senormechanico View Post
Sensibulbs aren't cheap, but they are very efficient, work between 8 and 30 or so volts, have great light spread, good light temperature and produce NO RFI.
I'm glad I bit the bullet. No financial interest, just a happy camper.

www.sailorssolutions.com
I bought about 20 Sensibulbs, they don't fit my fixtures!!

Shortly to be for sale
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Old 27-12-2011, 21:18   #9
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Re: Question About LED Power Consumption

I'm very grateful for all of the useful information! I'm sure this thread will be useful to many people.

BUT -- no one really answered the original question. The LED units I ordered use a buck-type power supply. The catalogue page says they are "constant current, no matter what the voltage". Literally speaking, that would mean that the power consumption (expressed in watts) would be double at nominal 24 volts, compared to using it with a 12 volt system, if the current (expressed in amperes or milliamperes). The idea of this puzzles me. Does anyone know whether this is really true? Or do they confuse power with current?
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Old 27-12-2011, 21:38   #10
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Re: Question About LED Power Consumption

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2) Switching regulators -- these put out a constant current too, but also consume a fixed (almost) amount of power regardless of the input voltage. These are probably slightly more efficient than the linear regulators, may be designed for a wider voltage range, and may be more expensive. Some of these can put out a bit of R.F. Interference, so make sure this won't be a problem for you. There are several switching topologies (buck, boost, buck/boost, with many ways to implement), but any of these should do the job. Look at the input voltage range specifications.
DH,

This does answer your question. A "buck" type of regulator turns the input voltage into a pulse stream, that charges a capacitor to a lower voltage, which is then current regulated, to supply the LED. Thus, the total energy consumed stays nearly the same regardless of the input voltage.

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Old 27-12-2011, 22:59   #11
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Re: Question About LED Power Consumption

I should have been more clear: A switching regulator -- any type -- will take a constant amount of power from the input supply. This means that if the LED lamp draws 100mA @ 12V (1.2W) it's going to draw 50mA @ 24V (1.2W). The regulator converts this input power to (say) 600mA @ 2.0V (1.2W) for the actual LED diode.

Of course in the real world the regulators aren't 100% efficient, so there will be slight losses along the way, and the power drawn will not be exactly constant. The differences are usually minor though.
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Old 28-12-2011, 00:16   #12
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Re: Question About LED Power Consumption

Thank you, thank you, for the clear information. The buck-regulated LED units sound like a wiener. SuperbrightLEDS sell 1.2 watt buck-regulated G4 LED units for $13. Just ordered a few to try them out.
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Old 28-12-2011, 18:15   #13
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Re: Question About LED Power Consumption

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Originally Posted by StringBimini View Post
S/V, what brand of lighting are you using for these local battery driven lights with door switches, and where did you order them? I had the same idea, and wanted to implement. Maybe you customized them, and if so, what list of parts? Pictures?

No pictures here at the moment, and I don't really have time to scan the diagram, but it's all electronic surplus store stuff. The 9V "locker lighters" are just a circuit closed with a magnetic switch. You can get little "medicine cabinet" LEDs powered by coin batteries with such switches; just add Velcro to stick the magnets in place. Open=on, closed=off.

My idea is just kicked up to regular 12VDC LEDs (brighter) with a 9VDC supply.

I got the LED strips from here: Marine LEDs Canada

For the locker lights, it doesn't matter if the LEDs are cheap and bluish (you can use yellow if you want), I got all parts from here: www.activesurplus.com.

For the IR step lights, there's a little more involved, but the circuitry is no different from any cheap movement detector circuit or even "The Clapper", I suppose. The interruption of the IR beam triggers the light, and a switch cycles it off once the beam is resumed. Haven't built this yet entirely as I'm thinking I want a "daylight off" switch which would involve a light sensor scavenged from a "Moonglow" type yard lamp ($5). In fact, maybe one of those little solar panels could provide enough juice to power the step lights and the IR circuit.

It's pretty basic stuff. I just hate paying WM $50 for ideas I'm capable of crimping together in 20 minutes. You could smarten it up by salvaging little half-moon, translucent fixtures from many a boat graveyard or consignment place.



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