LED calculation review required

[gilles0181]

Hi,

In search for my 'thunderstorm' idea; i have found this product:
http://www.ghl-store.com/alu-leuchtbalken/led-steuerungen/ledcontrol4active-2.html

Which is a dimmable LED-controller with driver, 4 seperate channels, 5-48V, max 5A dimming through PWM through GND without power supply.

If i read their pictures correct; i have a max. of 48v at my disposal; and all channels in sum should not exceed 5A.

Since 'thunderstorm flashes' are only produced on 2 channels; i am only going to connect these 2 and i wanted the brightest LED light available.
I came up with this; Cree XT-E Premium Cool White LED;
Max Current 1500mA
Recommended current 350-1100mA
Forward Voltage 2.85-3.4

Given the 2 channels; i can devide the 24V and 5A; which would mean i could have 24v + 2.5 on each channel (the other ones are not used)
So i entered the values in the calculator found here (http://ledcalc.com/#calc) tab "Series".

And i came up with this:
Supply Voltage: 24v
Voltage Drop Across LED: 3.4v
Desired LED Current: 1300mA (*)
How many leds connected: 6

(*) Entering 1300mA yields the result of 1090.9mA in the calculator; which is closest to 1100mA which i could find.

The result would be that i could connect 6 LEDs in series; with a 3.3 Ohm resistor.

Am i correct that i then could use 12 LEDs (separated over 2 channels) with 2x 3.3 Ohm resistor to use the driver at optimal level? Or am i missing something?

 

[byee]

Had a quick look at the product page. The answer is in the diagram just below it. The outputs are PWM used for dimming the LEDs.."¦"¦in this case simulating storms.

I hope this helps

 

[gilles0181]

That does not help to be honest The top diagram can also be used to do PWM; the bottom diagram is only needed if you have your own drivers (e.g. if the main unit does not supply the voltage or amperage what is needed).

I hope to get the answer if:
1) My current calculations are correct
2) The leds are the right choice for the job (lightning flashes)

Thank you

 

[mcgyvr]

1-No your calculations are not really correct.
Your supply voltage is supply voltage.. you don't divide 48 in half.. If your power supply is 48V then supply voltage is 48.. If you use a 24 volt supply your supply voltage is 24.. If you use a 12V supply your supply voltage is 12
and secondly.. that calculator is unsafe as it does not apply a safety factor to the resistor wattage.. If you ran it like that you would have had a resistor that was so hot you couldn't touch it.. ALWAYS double (or even triple) the "calculated" wattage for safety..

AND... I would never do it like you want to.. Its very inefficient to use resistors as current limiting devices for high power LED's.. Thats why there are constant current LED drivers.


2-ANY LED can flash... and seeing how you didn't describe the details of your "thunderstorm idea" we can't answer that question.

 

[gilles0181]

1-No your calculations are not really correct.
Your supply voltage is supply voltage.. you don't divide 48 in half.. If your power supply is 48V then supply voltage is 48.. If you use a 24 volt supply your supply voltage is 24.. If you use a 12V supply your supply voltage is 12

What i meant with 24v is that the calculator is only capable of going to 32V. To determine how much leds i could put on each channel i divided the 48v in half; but you are right; the voltage that goes into the driver still is 48v. I hope you now understand my 'noob-ism' approach

and secondly.. that calculator is unsafe as it does not apply a safety factor to the resistor wattage.. If you ran it like that you would have had a resistor that was so hot you couldn't touch it.. ALWAYS double (or even triple) the "calculated" wattage for safety..

AND... I would never do it like you want to.. Its very inefficient to use resistors as current limiting devices for high power LED's.. Thats why there are constant current LED drivers.

Since i am clearly missing some sort of background knowledge; what would be a better choice and at what mA would the leds be driven then?

2-ANY LED can flash... and seeing how you didn't describe the details of your "thunderstorm idea" we can't answer that question.

Here is a video of the idea in action; it is purely visual; the lights should not have any growth promoting capabilities but should be capable of lighting up the tank very well flash wise (and thus in my eyes should have a rather high light output).

At 1m40 seconds the Thunderstorm is activated using the Profilux 2:
http://www.youtube.com/watch?v=PgBFiKiljbk&t=1m40s

 

[mcgyvr]

First.. Do you even have a profilux or other reef controller?

As to resistors vs drivers..
Using resistors means you are "wasting" heat to regulate the current.. Resistors are commonly used for "low" power indicator LED's (20mA or less) because there you are only dealing with 1/2W or less of dissipation. Not a big deal but with energy efficiency stuff lately even that is changing..

When you get into the higher wattage LED's for lighting NO one would use a resistor to regulate the current.. As such we use LED drivers that are "constant current" power supplies that are much more efficient at regulating the current vs a resistor.

There is SO much information on how to build a proper LED fixture on here I'm gonna just leave it at that.. You can search...
Hint..
Meanwell LPF driver

 

[gilles0181]

Yes i have a Profilux controller; just no experience with DIY led and English is not my native language; i do appreciate the answers!

So; in conclusion you are saying;
Although the LED driver should be capable of running these kind of high power LEDs you really should avoid it since using the resistor to limit the current would be way to inefficient.

Thanx for the hint; i'll try to look it up.

 

[mcgyvr]

So; in conclusion you are saying;
Although the LED driver should be capable of running these kind of high power LEDs you really should avoid it since using the resistor to limit the current would be way to inefficient.

Yes... while its still not nearly the power consumption of a metal halide or t5,etc.. There is no point in going to a more efficient solution like LED's and then just wasting more energy with resistors when it can be done more efficiently using purpose built constant current drivers.

But I've never used the profilux nor do I know what they are capable of as far as dimming signals go so I can't be much help there (your english is great.. I only know how to say "ich liebe dich")

 

[zachts]

I couldn't get the page to translate for the profilux (darn old computer) and I am not familiar with it either but, anyway, the Meanwell LPF driver would not work well for lightning as it's response time is too slow to simulate lightning flashes. I have to assume that the profilux can output a 5volt pwm signal either with 255 steps of resolution (most common) or something higher 4095 steps is also common. Either way that doesn't really matter but the driver does need to have instantaneous response. The Meanwell LDD drivers paired with a voltage supply are great for this as are many other DIY drivers or other off the shelf drivers that utilize 5 volt pwm dimming.

There is a very large thread on the LDD drivers here for your reference:
http://www.reefcentral.com/forums/showthread.php?t=2222702

Hope that helps.

Also your english is better than mine (at least when I'm typing on this forum sometimes, and it's my native language) :lol: