DIY led panel - again

[edd07]

Goodmorning guys!
I've been going over lots of thread on this great forum about a diy led panel.
I'm quite new to electronics projects, so i've some questions.

My set up works on 4 strips LEDs:
1. 9 x Cree XT-E RB @700mA
2. 9 x Cree XT-E RB @700mA
3. 9. Osram Oslon 80 Hyper Red @700mA
4. 9. Osram Oslon 80 Hyper Red @700mA

They should be driven by 4 LDD-700L, with a 75W PSU.

-So, Cree LEDs and Osram LEDs, run @ different voltage @700mA (about 3,2V vs 2,6V ). Even if they are driven by different DLL units, is it a problem?

-Does the LDD units drain some voltage? If so, how much for each?

-Does the LDD provide exactly (except tolerance) the announced current?

- If i would add a PWM dimming control, does the all system consume the some power? I hope that i could low the LEDs brightness, running them @350mA, in some way that i don't know, and this configuration allowed me to use less power. Is there any way to achieve this?

Sorry, it seems i'm about 5 years old xD I swear i'm fully grown up :bounce1:


Thanks!:wave:

 

[perkint]

The LDDs will need you to supply them at least 3V more than the LED string requires (9 XTEs at 700mA will be about 27V so you need at least 30V power supply). You can supply them anything from that minimum to the 56V max of the LDDs (so in the case of the XTEs anything from 30V to 56V PSU).

The only way to reduce the current from an LDD is to swap it for a lower rating! The 700mA will regulate itself to put out 700mA at whatever voltage. All a PWM signal does is very rapidly turn the output on and off, so at 50% PWM you still get 700mA, but for only half the time so the light is only half as bright.

The LDDs do use some power. How efficient they are varies with the input voltage and the required output voltage, but generally they are over 90% efficient.

Tim

 

[edd07]

perkint, thanks for the quick respose!
I think I'm going to choose the PSU and then pick the right number of LEDs. (I think L series max voltage is 36V). Looking for the MW RPS-75-36.
Can the LDD drivers be powerd by a variable power PSU?

So, the only way to consume less power is to physically create two different circuits, one with the LDD 700L, and another one with the LDD350L? With two different PSU and switch to the less powerful one i mean.

Just one last question.
One the Cree specs sheet i didn't find anything about forward voltage @700mA.
There is neither any diagram about current-voltage relationship, nor a simple number, do you know where i can find it?

 

[perkint]

An LDD run on 50% PWM will use less power than on 100% but only as it is turned off for half the time. Why do you want lower power consumption? Just to save electricity?

There is a chart on the cree datasheets. Google "cree xte" and one of the first few results should be a direct link to the PDF with that info in it (a few pages in).

Tim

 

[edd07]

I understand that pwm can make LEDs consume less power, but the PSU will always supply the same wattage, isn't it?
Yes, it is just for electricity saving, or better, money saving

I already checked official data in the Cree website, but there is nothing about voltage @ 700mA, i can't understand why..

 

[oreo57]

arrow was for something else..

 

[oreo57]

I understand that pwm can make LEDs consume less power, but the PSU will always supply the same wattage, isn't it?
Yes, it is just for electricity saving, or better, money saving

Matching the PS to the driver is a bit of an electrical savings but w/ modern switching ps it is not much..nor is it worth bothering about..

You may have an issue w/ worst case PS like a 48V PS feeding a Meanwell w/ 1-3V led..

http://cds.linear.com/docs/en/solutions-manual/Power_Management_For_LEDs.pdf

http://www.digikey.com/en/articles/...end-acdc-converter-modules-set-new-benchmarks

http://www.networkcomputing.com/dat...data-center-it-power-supplies/a/d-id/1234016?

 

[edd07]

LoL it is like in a page by its own.
Thanks oreo57

I'm a noob, let me understand something.. Power units supply only the necessary voltage to activate the device? The power unit of course have an efficiency and i've understood depends from the load, but i thought it always supply their max power.

So the problem of the power consumption is only the psu efficiency, instead of the provide of the max psu voltage?

 

[perkint]

With a constant voltage PSU (ie a normal one) it will always give its rated voltage, but only the amount of current required. So if you run a 45V string of LEDs with an LDD 500, the power supply will give 48V, but only just over 500mA (therefore 24W). If you run a 21V string of LEDs with an LDD 500, the supply will still give 48V, the LDD will drop that to 21V for the LEDs, but now the power supply will only be supplying around 0.25A (therefore 12W).

And if you drop the PWM to 50% the power requirements remain the same, but since the LEDs are turned off for half the time, you only draw the wattage half the time, so use half the electricity

Tim

 

[edd07]

Ok, thanks! I've got the concept. This have been really helpful. But even if i have a more LDD units, in the same psu, requirements are the same?

Another question, about the led mcpcb. I've seen there are aluminium and copper ones. Is the difference so big in dissipating heat?

 

[oreo57]

Ok, thanks! I've got the concept. This have been really helpful. But even if i have a more LDD units, in the same psu, requirements are the same?

Another question, about the led mcpcb. I've seen there are aluminium and copper ones. Is the difference so big in dissipating heat?

CU is a better conductor of heat than aluminum.. That said mass/surface area also comes into play.. A large mass/surface area of aluminum will be better than a small mass/surface area of copper..

As to ps it is based on V(f) strings and watts required.. not so much LDD though obviously they are all related..

5 LDD's @ 1000mA requires a 5A power supply to feed them. Voltage depends on the series string added v(f)'s
PS watts is dependent on the VxA's..
5 LDD's @1000mA running 3 diodes @ 3v each would be ......... 45W ps @ 12V.. roughly speaking and not considering reserve power tolerances ect..
Running 5 ldds @1000mA and using say 2-20V chips in series per LDD 200W ps @ 43v
Same amount of LDD's different string parameters.


LDD's have no "voltage dependency" besides the min to run them and the max that frys them..

 

[perkint]

5 LDD's @ 1000mA requires a 5A power supply to feed them

Just to add - that is not aways true.

If you have a 48V supply, running LDD1000 would require 1A from your PSU if you are running a fV string of about 45V, but if that string is fV 21V, the LDD will only draw about 0.5A at 48V. Get the voltage of the PSU right (based on highest fV string of LEDs plus 3V for LDD) and then the wattage required of the PSU is simply the total wattage of the LEDs (plus extra to prevent driving the PSU too hard).

The LDDs will only draw the amount of current they need to get the power to run the LED string - their input current draw is not simply the same as their output rating.

Tim

 

[edd07]

Ok, I see these Meanwell driver are a really safe way to light up LEDs..

I'm sketching some electrical configurations to build up this LED panels, if you don't mind, i'm happy to share it with you =)

I think i'm going to set up a 80-90W dimmable panel based on 25-30 Cree XT-E Royal Blue running max @1000mA

Really thanks!

 

[perkint]

They are very easy, pretty versatile, efficient and safe. And fairly cheap. What's not to like

Tim

 

[oreo57]

Just to add - that is not aways true.

If you have a 48V supply, running LDD1000 would require 1A from your PSU if you are running a fV string of about 45V, but if that string is fV 21V, the LDD will only draw about 0.5A at 48V. Get the voltage of the PSU right (based on highest fV string of LEDs plus 3V for LDD) and then the wattage required of the PSU is simply the total wattage of the LEDs (plus extra to prevent driving the PSU too hard).

The LDDs will only draw the amount of current they need to get the power to run the LED string - their input current draw is not simply the same as their output rating.

Tim

Thanks for the correction.. to me it is just a "rule of thumb" where it would rarely be exceeded.
Take 5 LDD's @ 1000mA 3 strings at V(f) of 35V, 1 at 28V, 1 @ 12V
A 75W array..
W= VA
75=48x x
x=1.5A from the PS...A 31.2% drain on the PS Watt wise
Many ps run most efficient in the 50% range, though eff loss is usually minimal on good ps's
A 100W PS IS a better fit ..

Point is as a "rule of thumb" if they match the PS to the Meanwell total they "should" never get in trouble nor run too inefficiently (assuming they have a healthy amount of diodes)..

Maybe I should drop it.. but I can't see the "rule" hurting too much, though technically incorrect.

"Someday" I'll put a shunt resistor on the v(out) to LDD's line and see what it draws..

you tell people that they have 6-1A meanwells and you only need a 2A ps and they go blank..

 

[perkint]

Not a bad rule of thumb, but just thought it was worth mentioning

I've seen threads where people have used the same rule and bought a significantly more expensive PSU than was required, but if not sure, always go for more power - another good rule of thumb

Tim

 

[beolson25]

question on final spectrum

question on final spectrum

My set up works on 4 strips LEDs:
1. 9 x Cree XT-E RB @700mA
2. 9 x Cree XT-E RB @700mA
3. 9. Osram Oslon 80 Hyper Red @700mA
4. 9. Osram Oslon 80 Hyper Red @700mA

I know it is annoying but I wanted to ask ... Above you mentioned what looks like a 50% blue, 50% Red LED layout. Are you aware of what that will look like in an aquarium? If so, that is fine but it is really far from anything I have seen people use.

 

[oreo57]

I know it is annoying but I wanted to ask ... Above you mentioned what looks like a 50% blue, 50% Red LED layout. Are you aware of what that will look like in an aquarium? If so, that is fine but it is really far from anything I have seen people use.

Purple....

 

[beolson25]

Purple....

LOL ... Very good point ... now I'd actually be curious to see it ... :debi:

 

[oreo57]

LOL ... Very good point ... now I'd actually be curious to see it ... :debi: