Hi Everyone!

[bmamo]

Hi,
this is my first post after i have been reading around the forums for quite some time now.. Thanks for the wealth of information you provide :wave:

I did not really understand this driving LEDs by current instead of voltage.

Let me give you my scenario, I have bought the following:
http://www.ledrise.com/accessories/led-drivers/p240/led-driver-1000ma/
which says is a 1000mA constant current supply irrelevant of the voltage as long as it is in the range


and i was thinking of using it to drive the following LED i bought:
http://www.ledrise.com/leds/high-power-leds/p863/bridgelux-led-array-2200lm/

Forward Voltage (recom.) 15.1 V
Forward Voltage (range) 15,1-17,3 Min-max V
Forward Current (recom.) 750 mA
Forward Current (range) 750-2500 mA

If i am runinng it in its voltage range without the constant current power supply (directly connected to the batteries), how much current would it be getting? Would I burn it out?

thanks in advance!

 

[Th232]

The current it would get would depend on the voltage of the batteries. Without the datasheet I can't say how much it would get, but given how the info has been organised, I'd say that at 15.1V you *should* get that 750 mA. Bear in mind as well that there's a natural variation in Vf between LEDs, so (again, without seeing the datasheet) it's quite possible that you'll get a fair bit more or less than 750 mA.

 

[blasterman]

Hi there!

Well, for starters, the specs listed for the Bridgelux C2002 are incorrect. See Bridgelux's own tech spec here. The '106 lumen per watt rating' is pretty cute to, so something is getting lost in the translation on their site. Aren't you glad we're here :wave:

The C2002 is designed to run as high as 1500mA, and having used many Bridgelux arrays I tend to follow their specs pretty close. You can always run an emitter at lower current, but higher current is at your own risk.

If you want an emitter that can be driven at around an amp, then look at the Bridgelux C1202.

In a simplified nutshell, since LEDs transfer a lot of current with a small amount of voltage differential it's more stable and consistent to have a driver that delivers a fixed amount of current and varies voltage accordingly. This way you don't have to worry about anything other than powering the driver.

You can run LEDs with a fixed voltage supply or directly of batteries, but it's prone to a lot more variables and not the most ideal way to go. If you have a 12 volt battery you can run a C1202 directly off it since the emitter it rated for 12.8 volts. It just won't be nearly as bright because that .8 volts is going to make a big difference in terms of current.

Also, many low voltage DC in drivers require a couple volts 'head room' to run an LED of the same voltage. For instance, if you were powering this driver with a 12volt battery you wouldn't be able to push an LED with a forward voltage higher than 10volts or so. This rules out the Bridgelux mentioned above.

 

[bmamo]

Hi,

thanks for your replies :)

So if i supply the driver at 13.2V, i would get more or less 12V at the output but limited at 1A?

That should still drive the LED even though it's a lower voltage, but it won't be running at it's full potential, am I right?

Do you know of any high powered LED i can buy that runs at 12v and gives out a similar amount of lumens as the bridgelux?

thanks for all your help :)

 

[blasterman]

That should still drive the LED even though it's a lower voltage, but it won't be running at it's full potential, am I right?

DC current regulated drivers typically stop working or blink if the forward voltage of the LED side is too close to the input voltage. So, this isn't a good idea.

If you're looking for a single LED solution (flashlight) I'd check out a Cree MC-E, or possibly Phlatlight, but I'm not that familiar with the later.

If you can use more than one LED for your application things get easier. You could probably drive three Cree XP-G's in series off that driver with a battery source, and hit about 1,000 lumens at an amp.

 

[bmamo]

yes actually i have no space restriction. Aren't the cree xr-e better than the xp-g? if they work at 3V i would have to supply 12V for example if i run 4 in series? or should i wire them in parallell at 3V but supply higher current? which is the best setup you would recommend?

 

[blasterman]

The XP-G is the ideal emitter for portable applications because of it's high efficiency. Bridgelux kicks_butt, but they are primarily intended for fixed lighting applications where you want raw lumens over anything else.

I *suppose* you could run four XP-Gs in series off a ~12volt source without too many issues. The XP-G runs at 350mA at 3volts and 1000mA at 3.3 volts. So, if you can indeed get up to 13.2 volts you'll be running them at their rated brightest.

 

[bmamo]

Actually i'll be having 13.2v exactly :)
11 AA rechargeable NI-MH batteries in series and then in parallel to another 11 AAs so as to increase the mAh. Those should drive both the bridgelux and the crees.

As regards to charging the batteries, controlling the voltage and current i have a controller with which i can control both:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=220663964741#ht_6607wt_905

...but i still have to find out how it really works. Shouldn't be really that hard i guess. I thought i should be supplying 13.2V and 500mA so as to recharge the batteries since 1.2V x 11batteries = 13.2V

Then for the LEDs i cannot use the constant current module i bought (which i gave the link to earlier). It supplies up to 1A, but since i'm driving in series that means the voltage has to go up and the current remains at 350mA right?

Oh and by the way i gave the wrong link to the bridgelux i bought! Oops!:whistle: It's this one actually!

http://www.ledrise.com/leds/high-power-leds/p861/bridgelux-led-array-930-lm/

Forward Voltage (recom.) 11.6 V
Forward Voltage (range) 11,6-13,3 Min-max V
Forward Current (recom.) 600 mA
Forward Current (range) 600-2000 mA

 

[bmamo]

Oh and by the way thanks for your replies they're all helping me a lot :)