Fixed 12v lighting with XR-E

Thanks for the great resistor calculator link Veto, I especially like their Guru function!
Can someone who knows about these things, have a few plays, and tell us if its an accurate system or not?

Added to LED Fixed Lighting Index

Mash said:

Can you please elaborate a little on this?

1- how do u tell which kind of cell phone charger you have? I have lots of Nokia chargers sitting around with spec of 5v and 400mA, and some different ones also, so maybe i can start experimenting! Do you connect the LED directly to the charger or do you need resistors etc?

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The ideal type of chargers, the electronic switching kind, will be very lightweight -- unlike the typical magnetic ones which are bulkier and quite heavy. The Nokia chargers are exactly what I've used (and Motorola)

2-My understanding of the technicalities is limited, but im trying to learn, so isnt the 5v output too much for the Crees which are in the 3.5v range?

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The way that those chargers work is that they can supply up to 5v. However, they are current regulated, meaning the circuit will increase the voltage as needed until it supplies a steady 400mA (or whatever the rated current is). I have had LEDs running directly off these sorts of drivers without resistors -- since these are designed to charge batteries, which are very sensitive to being overcharged, they are very well regulated already. I would suggest sticking with adapters that are explicitly meant for battery chargers.

With the magnetic type, the voltage is usually just dropped from the outlet by some factor (10 to 1 for a simple 12V transformer) and converted to DC, but it isn't regulated at all -- a voltage spike in your house wall outlet could then cause a votlage spike in your circuit and could possibly cook your LEDs, unless you add your own regulator.

3- How many Crees can you run with one of these chargers? Am i correct that if you run them in parrallel, you distribute the 400mA between them, eg with 4 LEDs each gets 100mA?
Thanks in advance for your info!

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This is absolutely true. Running more Crees in parallel will increase the efficiency of them, and give you more light from the same amount of power. Higher voltage is needed to drive them in series. If you're underdriving them that much I woudln't worry about adding resistors.

That seems not to jive with what I've seen with people using a resistor between each emitter in other pics, have I figured something wrong?

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Two 1-ohms in between each LED will be the same as a single two-ohm placed before them. I know the picture you're referring to, that was simply done for convenience I believe to spread out the heating in multiple places, rather than concentrating it in a single large resistor.

2xTrinity :
Thank you for your further info, much appreciated!

Is there a way of finding out if you have a proper current regulated phone charger, by using a multimeter?

Hi all,

OK, I have quite a few of the phone wall chargers sitting around my house and am looking at this for illuminating my garage with 3 of the Cree emitters from Dealextreem. I'm going to use a Motorola chager that is rated 5.9v 400ma. I'm guessing since I won't even bee close to driving the
Crees close to thier potential, I won't need any resiters or drivers.

Guys, do you know how much electricity will be consumed with this project daily so I put it into some real money terms? I'm sure it can't be much over the course of a year, but I would like to know.

I'm also going to take a trip to HomeDepot or Menards and look at new fixtures for the garage that are more energy efficient.

Thanks,

Rob

Dx and Kai are now listing Led 120 volt bulbs. Unless you like the challange of making the solar panel idea work...just pop in a couple of Led bulbs!

Okay, now for a new direction. How about driving these regulated reflector/XR-E combos from Dealextreme?

I see that they take 3.6v - 9.0v and have an output of 900ma. I'm wondering if I could string 3 of these in series and drive them from a 12v source? Any ideas if that would work?

That is exactally what I was looking at. I plan on ordering 3 of the $12.50 ones and running them off of a wall wart.

Dealextreme has been down so much I can't get my order in.

Rob

I just ordered 3 of them with the OP reflector for a little better beam pattern. Looks like the rest of the regulation and LED are the same, but I could be wrong.

I may try to dig up a larger mah power supply to use. I think three of them might over power the 500mah wall wart I was planning on using.

I'll let you know how it goes.

Rob

OK, I have another question which might be silly, but here goes:
When using a constant current driver, whats the Wattage needed on my power supply depending on my LEDS? On the constant current driver spec sheets eg this one I see input voltage/output voltage etc, but no mention of the wattage needed for the input.
Also I see all the resistor calculators etc, but I havent seen the PSU wattage mentioned anywhere?
eg if Im running 3 crees at 3 watts, do I need a PSU capable of minimum of lets say 10 watts?
Im trying to learn so please bear with me!

After Hurricane Katrina, I was very glad that I had kept quite a few sealed lead acid batteries regularly charged. I keep all the old "dead" ones from UPS's that I do battery replacements in. I used them for to power 12v fans I had pulled out of computers. The amount of air flow they produced was just enough to make life bearable at night while trying to sleep. Of course this isn't light related, but there were batteries involved! I had plenty of lights around to help me watch the fans spin.

We're closing on our first house in two weeks. There isn't really good exterior lighting at the new place. One of my first projects is going to be LED based exterior lighting. I'm thinking of using three LED clusters create floods, with local drivers (haven't decided on what to use yet.) I'm going to have a 12v bus supplying power, so the drivers will be at the cluster mount points. My utopic idea is to have someone way of remotely controlling the output levels of the drivers, which would require additional wire and a central control point (possibly microcontroller based).

With the project centrally powered, I can power it from mains via a hefty 12v supply and charge batteries at the same time during good times. I can later add solar power when the budget permits and have renewable power in bad times.

The extension of the project will then be to bring the lighting inside. I'm trying to design it in a way that will provide for ease of scaling. This is all a pipe dream right now... hopefully summer will turn things into reality! This forum has really helped give me some GREAT ideas!

Quote:
3- How many Crees can you run with one of these chargers? Am i correct that if you run them in parrallel, you distribute the 400mA between them, eg with 4 LEDs each gets 100mA?
Thanks in advance for your info!
This is absolutely true. Running more Crees in parallel will increase the efficiency of them, and give you more light from the same amount of power. Higher voltage is needed to drive them in series. If you're underdriving them that much I woudln't worry about adding resistors.

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what about if you ran them in series? would it give each one 400mA still or would it give them 100ma?