Driver for lots of LEDs?

Mash · Jul 31, 2007

I am thinking of doing a Cree yard lighting setup for a friend, therefore been looking at drivers AGAIN!

So far with the all drivers (AC and DC) I have seen, the maximum number of LEDs I could run off one driver unit is between 6 and 7 (calculated on a rough 4Vf for the Crees) at 700mA. I could probably do 12 (DC 4015 Boostpuck )to 14 (Lumidrives) but those are at 350mA; so close yet so far!

So given the above facts, and the obvious preference of not having to purchase/wire lots of drivers, the question is
what are the drivers that power the highest number of Crees at 700mA or higher currents? How about at 350mA, if we prioritise quantity rather than current?
I think I will eventually hit a voltage wall, eg since 20 emitters would need 80V flying round the circuit, ie almost US mains, which wouldnt make me feel too safe about it!
As a counter argument, for Crees (from their data sheet):
350mA 80lm
700mA 136lm ie less than double output at double current
1000mA 176lm
By personal experince, is it better to drive them at a higher current, or have more emitters at a lower level as suggested by above data?
Opinions?

monkeyboy · Jul 31, 2007

Are you running this off mains or battery?

Mash · Jul 31, 2007

Mains, in Europe, 240V.
Would love to do a solar/battery automatic system addition later on, but thats another story for future!

winny · Jul 31, 2007

Mash said:
By personal experince, is it better to drive them at a higher current, or have more emitters at a lower level as suggested by above data?

More emmitters at lower current will give you better efficiency, but high cost due to many LEDs.

How many do you need to run?

Mash · Jul 31, 2007

Its a big yard, two sections. Need to experiment a bit, but I think 20 or so emitters.
I have played with some lenses but not very happy with them. So need to try some reflectors. Are there reflectors that are tottaly flood, ie no hotspot at all?

winny · Jul 31, 2007

Are you planning to run all of them in series or in several sections? How high efficiency do you need? A quick an dirty solution would be to use a PC PSU, with seven groups of three LEDs with one resistor in each, or four in each and no/very small resistor. Lots of wire but very cheap.

Mash · Jul 31, 2007

Sounds interesting, Thanks!
Could you please elaborate?
Wouldnt four LEDs require 16Vs? Are you suggesting to have 3 LEDs in series, 7 groups of them running in parallel off 12Vs?

I can do all together or sections, since its a total project.

My question regarding the driver for high number of LEDs is also being asked for reference, for future internal house lighting as well.

PS you just got me thinking! Wouldnt I be able to run 6 Crees, if I tap the PSU on the +12 and -12 lines (therefore giving me 24Vs)? Or if I needed lets say 17V to tap +12 and -5?

WeLight · Jul 31, 2007

Hi
You might find this boost driver the solution

Basic specs are 4V - 30V input.
Boost converter, so input voltage < total Vf.
Input current max of 5A.
Output voltage max 45V (make number of series connected LEDs)
Output power max 45W.

It's a bit tricky in terms of specific capabilities. A couple of examples would be if you had 6V input and the 5A max, means a total of 30W input power. That means about 25W output power (less losses) and so if you had say 40V worth of LEDs you would be driving them at 25W/40V so about 625mA max. If you had instead 20V worth of LEDs then you would have 25/20 = 1250mA max.

If you had say 12V input, and 5A max. That's well over the limit of 45W and so the 45W would become the limiting factor. So, with say 40V worth of LEDs you would be able to drive up to 45/40 = 1125mA.

You can see from the picture the blue trimpot on the board, it is a multiturn trimpot and allows the user to set the output current quite accurately. Output current is stable and regulated.

At 45W output the heatsink will get reasonably hot and a little airflow wouldn't hurt...

The board is 2.5" x 1.8", components only on the top surface. The new design will have open circuit protection. It will clamp the output to around 45V max if the load is accidentally removed.

That is one danger of most current regulating boost converters - they will self destruct if the load is disconnected because they will try to drive infinite voltage at the output to try and get current to flow & regulate.

Cheers
WeLight

Mash · Aug 1, 2007

Thank you very much WeLight, for your detailed explanation and information! That is how I learn best! Now I can figure out Xitanium driver specs as well, since before your explanation didnt undertand what current they would be supplying!

Also having just got my head around the output side, I am trying to figure the input side as well! I need to watch the current capabilities of the input side as well, i can imagine it being difficult trying to find eg a 6V 5A (and no more) PSU! Is there an overcurrent protection on the input side? EG if your input is a PC PSU with a very high current capability.

I am begining to think a mains solution such as Variled would suit this project best. Since the installation is for someone else, who wont be tinkering or fine tuning it; it can do about 14 crees at 350mA which should be enough; and has a dimming function also. What is your experience with Lumidrives, since you carry them also?

Funnily enough I was thinking of your Cree XR-E Q2 Light Engine, as a quick solution for the emitters (great CPF price!)! Which optics/reflectors would you reccomend for PURE wide area flood? Obviously you want even illumination on your yard, with no hotspots!
Also your site mentions Constant Current Driver ICCD-0012 as suitable drivers, but I cant seem to find it or the dimmer on your or the manufacturers site.
(EDIT: ICCD-001 driver specs mentions running 18 LEDs at 350mA!!! Your experience of this item would also be appreciated!)
Everybody please keep the info coming, for me and others future reference!
Thanks all!

knabsol · Aug 1, 2007

Hi!
I think I´m on the same track as you. I´m constructing a outdoor lightning system for my garden/walkway. I will use about 25 Luxeon rebels for this. As the distance is long my idea is to run a cable with around 24volt and then have a small step down circuit with each LED, probably a simple switcher. So I will be able to run them from anything between 5 and 40volts without too much losses. Hopefully I´m making it solar powered in the future too.
But WeLights board looks really nice! Is it buck/boost or only boost?

Argofanatic · Aug 1, 2007

I can speak from experience !

I've just finished installing two walkways using luxeon K2's.

1 walkway has 10 fixtures, 2 parallel strings of 5. Spacing is 16' between fixtures on each leg, each leg is staggered at 8' (basically 8' between a left fixture and a right fixture). Each leg therefore is 80' long (5 x 16'). The first Xitanium driver I used (1500mA) gave me 700mA per leg. My wife complained that it was too bright (can you believe that) so I put in 1000mA giving me 500mA per leg. Still plenty bright.

Walkway number two has 12 fixtures. 2 parallel strings of 6. I buggered up my wiring (conformal coated) but that ended up being good thing. Each fixture has a cool white and a royal blue K2 in parallel. So each side of the walkway has 6 fixtures in series, each with two leds in parallel. This configuration is driven using the 1500mA Xitanium which works out to roughly 700mA per leg, and 350mA per led. Plenty bright again for the same spacing as walkway one described above. The white and blue combination is much more pleasing to the eye than the plain cool white. The run length on this second walkway is 6 x 16' = 96'.

So far, very happy with my implementation. The wiring should rot before the led burn out (in theory anyways).

WeLight · Aug 1, 2007

Mash said:
Thank you very much WeLight, for your detailed explanation and information! That is how I learn best! Now I can figure out Xitanium driver specs as well, since before your explanation didnt undertand what current they would be supplying!

Also having just got my head around the output side, I am trying to figure the input side as well! I need to watch the current capabilities of the input side as well, i can imagine it being difficult trying to find eg a 6V 5A (and no more) PSU! Is there an overcurrent protection on the input side? EG if your input is a PC PSU with a very high current capability.

I am begining to think a mains solution such as Variled would suit this project best. Since the installation is for someone else, who wont be tinkering or fine tuning it; it can do about 14 crees at 350mA which should be enough; and has a dimming function also. What is your experience with Lumidrives, since you carry them also?

Funnily enough I was thinking of your Cree XR-E Q2 Light Engine, as a quick solution for the emitters (great CPF price!)! Which optics/reflectors would you reccomend for PURE wide area flood? Obviously you want even illumination on your yard, with no hotspots!
Also your site mentions Constant Current Driver ICCD-0012 as suitable drivers, but I cant seem to find it or the dimmer on your or the manufacturers site.
(EDIT: ICCD-001 driver specs mentions running 18 LEDs at 350mA!!! Your experience of this item would also be appreciated!)
Everybody please keep the info coming, for me and others future reference!
Thanks all!

Yes the Variled is a nice solution and you have the option of dimming on the 'fly'.The ICCD-0012 is a no go, however the variled will drive the light engines and you can use some Fraen or Carclo 25 Degree optics to provide nice spill of light
Cheers
WeLight

Mash · Aug 1, 2007

Thank you fo ryour reply!
I asked about the ICCD-0012 since thats what the website says; however I couldnt find them on the website!
As you say "no go", are they not available at all?

WeLight · Aug 1, 2007

Mash said:
Thank you fo ryour reply!
I asked about the ICCD-0012 since thats what the website says; however I couldnt find them on the website!
As you say "no go", are they not available at all?[/quote

No not from us at least
Cheers
WeLight

winny · Aug 2, 2007

Mash said:
Could you please elaborate?
Wouldnt four LEDs require 16Vs? Are you suggesting to have 3 LEDs in series, 7 groups of them running in parallel off 12Vs?

...

PS you just got me thinking! Wouldnt I be able to run 6 Crees, if I tap the PSU on the +12 and -12 lines (therefore giving me 24Vs)? Or if I needed lets say 17V to tap +12 and -5?

Looking at the datasheets, 3 V on each LED is a bit low, giving you about 60 mA. Very efficient, but not so bright.
Yes, three in series with two ohm in series will give you 750 mA. It would cut down the efficiency to 88% of direct drive, but since PC PSUs are free, you can run it for a very long time until you can capitalize the cost for a better and more expensive solution.

Regarding using the minus-rails from the PSU, it's unlikely that you can run more than one or two from one PSU since they usually provides about 1-2 A on those rails. Apart from that, it's a good idea. Another solution would be to use two PSUs to create 24 V, so you can run seven in series, probably without a resistor.

glire · Aug 2, 2007

PC PSU are quite big IMO.
I suggest a Cisco PSU. There are some of 3.3V up to 4.5A, they can be available for cheap (at least I could get one locally for 5€). I think 9 or 10 LEDs could be direct driven safely, and in parrallel. Running LEDs in parallel under a fixed voltage slightly below the "typical" Vf should not compromise any LED, even if one dies or burns. 3.0V might be too low, 3.5V might be risky, 3.3V is a good safe voltage for DD IMO (and 100% efficient, no losses in a balast).

winny · Aug 2, 2007

glire,

Yes, they are big. Perhaps Mash should elaborate some more about his needs.
I would myself not run them direct drive in parallel, but it should work. They will probably not be equally bright though.

Mash · Aug 3, 2007

Hello all, thanks for your input!
Winny:
Regarding the PC PSU, I also had concern about the -12v rail, since they usually supply 1-2A as you said. SO what happpens if I connect +12V at lets say 10A and -12V at 1A? Whats the resultant current of my 24V ?
Also re your suggestion fo two PSUs to give 24V, is this done by just connecting them in series, ie + to -?

Regarding the project itself, as I mentioned before, since this installation is for a friend, who is not an "enthusiast" and will therefore be unable to tinker and finetune it, I am inclined to use a commercial mains driver, plus two of WeLight's (CUTTER) 6 Cree light engine, which seem like a good deal and easy to use.
As a heat sink I feel like using a PC CPU heat sink and fan combo. However that leads to two issues, first the fans are 12V, so need to resistor them if I run them off the same circuit as the LEDs (eg for 6 would be 24V), and I have no idea what this would do the cicuit and supply to the LED. Otherwise I either have to find 24V fans, or run a seperate 12V line to the fans, or use passive heatsinking.
2-the light engines are 83mm in diameter, so the question is which heatsink has the largest flat base area for maximum contact with the light engine? I am sure this is related to the CPU types, so any PC experts opinion is welcomed.

winny · Aug 3, 2007

Mash,

Then you will have 24 V and 1 A.
Yes, exactly in series. If you friend is low on money or you don't find a good driver for mains voltage, I would say it's a cheap/decent solution.

momanz · Aug 3, 2007

How about laptop (18-19 volts/ 4-6amps) or inkjet printer power supples (24-32 volts <depends on printer> at 1-2 amps)?

Driver for lots of LEDs?

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