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#1 2018-01-15 00:34:00

Bx3mE
Member
Registered: 2018-01-09
Posts: 5

Noob LED 101 - Building a UV led array 3W Diodes

I am designing my own printer and have all components sittin on my desk except the uv leds.
To get as even light distribution as possible I am considering to use 242 3W 395nm leds. (dont ask why i need 242 of them - i just do... smile )
Now how do i wire them?

My design layout suggests having 22 series with 11 in each series. Since i dont want to design my own cunstant current supply i turn to e-bay/AliExpress and see most shelf products are designed for having 10 leds in series and, for the current specified, number in paralell.

Most supplys have 20-36V Forward current and 1W leds are commonly 3.4-3.6V meaning 10 in series make for a good match.
So far so good - same goes for my 3W leds.

Now starts my confusion.
Product sheet of the leds vary, specifying from 500mah for some up to 700 or 830mah with a 500mah beeing most common.
Questions:
1) If they are 3W as specified 830mah should be the correct value to do my math with or am i wrong? If 500mAh is correct how can 0.5A*3.6V=3W? To me that sounds like 1.8W... If 3W LEDs are only marketing gimmic and in fact are 1.8W is it the same for the drivers, 100W driver in fact beeing a 60W driver?

2) If i use 11 leds in series instead of 10 will it put the driver in over voltage protection/fry the driver? What will happen?

3) Putting 10 in series would leave me with 24 paralells which of course would be devided in several sets. Maybe 10x5. If 700mah is the value to calculate with for a 3W led then 700mah * 5 = 3500mah which i can find a "100W Led driver" for. Is this correct?

4) same as 3) but if i have to do my math with 833mah i am not likely to find a suitable driver... Should i then pick one with higher or lower current rating? What about voltage rating, over or under?

For reference These are the leds and drivers i am looking at right now:
Drivers:
https://www.aliexpress.com/item/DC12V-2 … 262.lYKFnx (22pcs of 30W)
or
https://www.aliexpress.com/item/High-PF … 268.lYKFnx

And Leds:
https://www.aliexpress.com/item/50pcs-H … 271.lYKFnx
or
https://www.ebay.com/itm/263074387501?var=562075025379

Any help is valuable!!

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#3 2018-01-15 07:58:01

laopa
Member
Registered: 2017-03-01
Posts: 10

Re: Noob LED 101 - Building a UV led array 3W Diodes

HI,

LED are working like this:
You will need a driver for LED with constant Ampere. Mean the Ampere will never change, but the driver will use the voltage to adjust and come to the total watt needed for the LED.
If your Led specification is 3.4Volts / 800mA.
You need to find a drive for 800mA. the voltage will be according to the number of LED place in SERIAL.
if you use 10 LED, then your driver must be 800mA and voltage over 34 volts.
if you use 20 LED, then the driver must be 800mA and voltage over 68 volts.

If you place too many LED, the driver will increase the voltage automatically, until reach the 800mA, if it is protected, then it will shut down, else it will burn.

I have try led array with big driver and 15 LED at 3W, also install lenses to concentrate the spot light, the problem is center of LED is very bright, between them less, so the print have not good even curring. Solution is to move the LED array more fare from LCD screen but you lose power.
So i change back to SMD LED very compact, and mirror metal cone reflector like the KLD.

Wish it help.

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#4 2018-01-15 09:54:51

Bx3mE
Member
Registered: 2018-01-09
Posts: 5

Re: Noob LED 101 - Building a UV led array 3W Diodes

Ok so i tried the LED Array Calculator.

If I use 40Volt powersupply i can use 11 LEDs in Series and 22 paralell - perfectly matching my needs.
The calculator says the solution will draw 15400mAh. Now the Calculator also suggests to add a 1ohm resistor to each series to limit current. Will adding this 1ohm resistor eliminate the need for a constant current supply?
Could i power the array (11+resistor x 22) with only a switched psu (like below) and nothing else?
40V 25A (1000W) Switching PSU AC/DC 220V - https://www.aliexpress.com/item/1000W-4 … autifyAB=0

Can i use a varistor instead of a resistor to control intensity of each series?

My input to the Calculator
PSU 40
FWD Voltage = 3.6
FWD Current = 700
Number of leds: 242

Calculator result:
Solution 0: 11 x 22 array uses 242 LEDs exactly

The wizard says: In solution 0:
each 1 ohm resistor dissipates 490 mW
the wizard says the color code for 1 is brown black gold
the wizard thinks 1W resistors are needed for your application
together, all resistors dissipate 10780 mW
together, the diodes dissipate 609840 mW
total power dissipated by the array is 620620 mW
the array draws current of 15400 mA from the source.

Last edited by Bx3mE (2018-01-15 12:56:00)

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#5 2018-01-15 19:05:36

Bx3mE
Member
Registered: 2018-01-09
Posts: 5

Re: Noob LED 101 - Building a UV led array 3W Diodes

I made an experiment to prove myself right or wrong... I used a car battery to power a LED i had im my spares box...

Led was 3W, 3.6V 700mA

(+)12V -> LED (+)
(-)12V -> 10ohm resistor (10W) ->  5ohm resistor (10W) -> LED (-)

It lit up perfectly and i could measure 3.56 volts over the led.

So in theory (11 LEDs+1ohm resistor in series) x22 in paralell should run fine on 40V 25A switching PSU.

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#6 2018-01-18 18:12:55

Bx3mE
Member
Registered: 2018-01-09
Posts: 5

Re: Noob LED 101 - Building a UV led array 3W Diodes

Next part will be designing the array. Does anyone know how to calculate heat dissipation?

My intended arrangement of the diodes is tighter than the pcb version would allow for so I am concerned about getting rid of heat generated by the diodes. Is the ammount of heat generated by 30 x 3W diodes the same as by a single 100W diode array?

How long do cooling fins have to be?

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#7 2018-04-24 01:00:22

Bx3mE
Member
Registered: 2018-01-09
Posts: 5

Re: Noob LED 101 - Building a UV led array 3W Diodes

My build has begun and I am coniniousy posting on Google+ until done. Since i have asked here i want others to be able to follow up.
I am also doing a instructable... Se links:

https://plus.google.com/communities/109 … 7401814291

https://www.instructables.com/id/SLAM-S … D-Printer/

Cheers and thanks for help...

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#8 2018-07-06 18:24:35

Sint
Member
Registered: 2018-06-06
Posts: 6

Re: Noob LED 101 - Building a UV led array 3W Diodes

Always nice to see other peoples builds. Thank you for sharing.

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#9 2018-07-08 19:47:22

bootdsc
Member
Registered: 2018-06-05
Posts: 7

Re: Noob LED 101 - Building a UV led array 3W Diodes

Interesting thing is those LED's are not quite what they claim to be, the max output for each LED varies due to poor qc. It ranges between 1.6w to 1.9w and the UV output is more like 390nm to 410nm which is actually a good thing when trying to get the light to pass through a LCD.

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