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Discussion Starter · #1 ·
Hi all,
I was looking for information on LED's and found some great information here so I joined the forum.

I have a question about PSU requirements. I've looked through lots of threads on various forums but couldn't find the answer I was looking for.

How do I calculate the voltage, amperage and wattage of an LED array so I can get the correct PSU ?
I intend to have several "strings" of LED's with each string controlled by a buckpuck (and hopefully the buckpucks controlled by an arduino for dimming etc.).
I'm thinking of 6 strings with 3 LED's in each string (so 18 LED's in total).
I intend to use cree xr-e with probably a 50/50 mix of cool and warm whites.

Any information on PSU requirements would be most welcome.
 

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You will have 3 LEDs in series in each string. If those are Cree LEDs the voltage when they are on will be from about 3.1 to 3.6 volts per LED, or from 9.3 to 10.8 volts for each string. That means you can use a 12 VDC power source. Each string will draw from about .5 to 1 amp, so with 6 strings in parallel they will draw from 3 to 6 amps total current. The power source must be capable of supplying more current than that, because it doesn't work well running an inexpensive DC supply at its maximum current full time. Assuming you have the high powered LEDs, you would want the supply to be capable of at least 8 amps, in my opinion. However, a buckpuck between the power supply and the LEDs means the LED current isn't exactly what the power source supplies. That might make it prudent to have a bit more current capability, or possible to have less.

12 VDC power supplies are cheap for low current, so you could save money using multiple power supplies, each powering a few parallel stings.
 

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This setup: 220VAC->12VDC->LED is not very efficient.
I would recommend a MeanWell LED driver in the 20-30W range with dimming. This can be cheaper and more efficient.

BTW what are your tank dimensions?
 

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This setup: 220VAC->12VDC->LED is not very efficient.
I would recommend a MeanWell LED driver in the 20-30W range with dimming. This can be cheaper and more efficient.

BTW what are your tank dimensions?
If he wants to control various LEDs at different currents vs. time, the Meanwell driver wouldn't work. If he doesn't mind controlling the current to the LEDs as a single variable, I agree that a Meanwell driver is an ideal, economical solution.
 

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Discussion Starter · #5 ·
You will have 3 LEDs in series in each string. If those are Cree LEDs the voltage when they are on will be from about 3.1 to 3.6 volts per LED, or from 9.3 to 10.8 volts for each string. That means you can use a 12 VDC power source. Each string will draw from about .5 to 1 amp, so with 6 strings in parallel they will draw from 3 to 6 amps total current. The power source must be capable of supplying more current than that, because it doesn't work well running an inexpensive DC supply at its maximum current full time. Assuming you have the high powered LEDs, you would want the supply to be capable of at least 8 amps, in my opinion. However, a buckpuck between the power supply and the LEDs means the LED current isn't exactly what the power source supplies. That might make it prudent to have a bit more current capability, or possible to have less.

12 VDC power supplies are cheap for low current, so you could save money using multiple power supplies, each powering a few parallel stings.
Thanks for this.
I read somewhere that you also have to allow a further 2V for each buckpuck ?

Tank dimensions are 36x12x18 deep.

Merry Christmas.
 

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18 XP-G LEDs are OK for this tank.
If you buy a 24V PSU you will be able to use 7 LEDs @350mA per buckpuck
12V PSU - 3 LEDs @350mA per buckpuck
 

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For things like this you need to start thinking in terms of watts and not amps. Watts are voltage independent. I use old laptop power supplies for these projects. Most laptops are 19v and like 60-90w. I use the buckpucks from ledsupply.com.
Remember that leds are current mode devices and that the controllers change voltage to keep a constant current. They are basically very small switching power supplies. Running them as close to their max rating will maxamize their efficiency

Sent from my DROIDX
 
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