Did i get the voltage and the resistor right for this led horticulture light ?

Discussion in 'The Projects Forum' started by steam29, Nov 24, 2018.

  1. steam29

    Thread Starter New Member

    Nov 24, 2018
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    i need help seeing if this pcb will even work or not its my first build ever so please be gentle.

    this is the finished auto routed board pic 1 https://imgur.com/fLj6EBy

    this is the shcematic pic 2

    the led i am using x4
    https://www.mouser.com/ProductDetail/Cree-Inc/XPEEPR-L1-0000-00901?qs=sGAEpiMZZMt82OzCyDsLFMPnZBpgzwT/jqrvO0i/wtI=

    i am running on a 12v cc input to a barrel jack, i noticed the jack didn't have a negative so i just grounded each end of the series. the ground at each led is how i think the manufacturer says to run it because its just a heat sink. i think at this setup with the 2ohm resistor i should be right up against 1 amp max per led which i think is good because horticulture lights are supposed to be bright right ?

    some questions i had where if i split the power into series from the 12v will it split the power to 6 v? heres an example of how i had it set up first but my friend said that it would split the 12v to 6 volt for each branch of leds whereas my dad says it wont. pic3

    another question i had was in a barrel jack i noticed it has this weird positive, gnd then gnd break and i tried to read and explanation about it but what i got from it was that if your not using it you can just gnd them so hopefully i did that right.

    the led will be on like 12 hours a day so if theres anything that i can do to make it safer let me know!

    Thanks so much guys ! this is my first post here so im sorry if i broke the meta or something.

    MOD: uploaded your image.

    AA1 24-Nov-18 07.59.gif
     
    Last edited by a moderator: Nov 24, 2018
  2. steam29

    Thread Starter New Member

    Nov 24, 2018
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    Last edited by a moderator: Nov 24, 2018
  3. oz93666

    Distinguished Member

    Sep 7, 2010
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    Have you already bought the leds ??? if not I would advise not to ..

    They are for manufactures to use , and have no heatsink ... also the power is so low , 4 of them will produce enough light for about 10cmx10cm ...
    What are you using these for ... I have a experience with a wide range of grow lights , you will be able to buy a complete product from eBay at a fraction of the price.
     
  4. steam29

    Thread Starter New Member

    Nov 24, 2018
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    i thought you could just put the copper pcb on to a heat sink ? i guess not lol and i was just trying to start a project of making my own pcb and i grow plants inside a space bucket and i already have my main cobs going i just thought it wouldnt hurt to fill in some of the gaps the 3500k leds have. i was having alot of fun learning how to do it but yea my boards pretty bad lol any ideas on something i can make that would be beneficial ? i only grow one plant per bucket so not alot of room to cover.
     
  5. oz93666

    Distinguished Member

    Sep 7, 2010
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    The main thing is heat sink ... the heat must be dissipated from the leds , which I don't think your design would allow ...

    This is a very big subject . Best to start with knowing where your power is coming from ... if the mains then these are hard to beat ...

    [​IMG]
    They have their own electronics built in so run directly from mains, and the spectrum is designed for plants ... only a 3 euros euros each for 50W!!! That is unbeatable , will need a good heat sink ....

    Big units like this will not be as efficient as lamps which use many small leds like these ...

    [​IMG]
    don't trust the W advertised on these .... a 30W lamp I bought only consumed 8W , even so the price is OK ... eBay is the place to look ...hundreds of different products .
     
  6. steam29

    Thread Starter New Member

    Nov 24, 2018
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    i already have some cobs in my bucket, i just wanted a project i guess that would benefit me in a way so it wouldn't be a waste lol. i guess ill read the ed tab on this website and learn more and try again when i have more knowledge.
     
  7. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    You should check the datasheet. It will answer all of your questions.
     
  8. steam29

    Thread Starter New Member

    Nov 24, 2018
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    acoroding to the data sheet im running the leds at the right apmerage and full volts but a guy said they would be dim so i dont understand
     
  9. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    LEDs normally run at some voltage drop (for example we will take "2VDC" here). If you run the LED at "2VDC" with a current limiting resistor and a "5VDC" power supply. The resistor will decide how bright the LED is. The voltage drop is always "2VDC" but if the current increases, the brightness will increase also. This is within borders of course, for normal LEDs the maximum is "20mADC", so you can run them on "15mADC" to be sure that they wont burn and get the maximum brightness.

    For your LEDs you should have the same. You need to power them with a certain voltage and by increasing or decreasing the current within the borders from the datasheet you will get different brigthness, however don't forget about the heatsink as you might burn them.
     
  10. steam29

    Thread Starter New Member

    Nov 24, 2018
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    so its possible to increase current without increasing voltagE?
    idk what current my power supply is pushing but my firend told me that at 12v with thhat resisitor we should be getting good current for the leds but the other guy in this thread said that they would be really dim so idk what to believe, im just reading the text book on this page to hopefully learn more. with the way my pcb is set up now would it work/ be safe? it would make a neat Christmas gift for the friend that helped me.
     
  11. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    I have to check the datasheet to say for certain. I don't have time at the moment.

    Normally: Yes its possible to increase the current without increasing the voltage. What is the current needed for your devices I don't know. The resistor controls the current, if there is no resistor the current will grow too high and burn the device.
     
  12. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    You aren’t clear as to what color LED you are using. The Cree has several red LEDs. Assuming a plain red COB, each unit will take 2.3 VDC. And will require 700mA (max). Well use 600mA for reliability. Four units in series will draw 2.3x4=9.2VDC.

    So for a 12VDC source, we will need to drop 2.8VDC. Using Ohms law, the required resistor is 2.8/.6 or a 5 ohm resistor.

    Since I’ve never used this particular device, these calculations are based on what one would consider for normal LEDs.
     
  13. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    Also the resistor will be "0.600ADC*2.8VDC = 1.68W", meaning it needs to be at least a "2W" resistor. "5W" is better.
     
  14. steam29

    Thread Starter New Member

    Nov 24, 2018
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    https://www.mouser.com/ProductDetail/Cree-Inc/XPEEPR-L1-0000-00901?qs=sGAEpiMZZMt82OzCyDsLFMPnZBpgzwT/jqrvO0i/wtI= i actually linked the leds in the main post
     
  15. steam29

    Thread Starter New Member

    Nov 24, 2018
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    is the 2w resistor based on what you commented or based on the pcb i tried to create?
     
  16. ArakelTheDragon

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    Nov 18, 2016
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    Its based on what @djsfantasi commented. We have to know your real device and check the datasheet to say for certain.

    EDIT:
    This is what we needed:
    If - Forward Current:
    350 mA
    Vf - Forward Voltage:
    2.1 V
    Power Rating:
    3.5 W
     
  17. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    I see the LEDs are "RED". Thats not very good for illuminating or flashlights. "RED" colour is only used for "Danger" signalization as the human mind accepts "RED" as something to be alert by!

    If you have 4 LEDs, that means "4x2.1VDC = 8.4VDC" power supply is needed only for the LEDs. The current is 350mA maximum, if there are no peaks and your power supply is good, you can choose "300mADC" as the nominal current. That means:
    "12VDC - 8.4VDC = 3.6VDC" => Voltage over the resistor
    "3.6VDC/300mADC = 12Ohm". => Resistor value
    "3.6VDC x 300mADC = 1.08W" => The resistor should be "2W" for a "12VDC" power supply. Are you using a battery power supply or something else?
     
  18. steam29

    Thread Starter New Member

    Nov 24, 2018
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    Well I'm hoping to be able to use a barrel jack as the main plug to the board and then bolt it onto a recycled cpu heat sink and then plug it into my dad's solar panel batteries that he set up (he's an electrician pretty much so he's got everything set up perfect) the lights are actually horticulture lights to add some extra supplemental to my space bucket( about 1ft wide walls and like 4 feet tall) this way if I do get it printed (as my first PCB project) I have an actual use for them other than being a pretty cool project to learn basic electricity from. Man I just learned so much from your simple comment lol, so if it's 1.08 you round up to 2w resistor right ? And that's what I would be buying a 2w resistor or a 120ohm resistor? Thanks so much for the help btw
     
  19. steam29

    Thread Starter New Member

    Nov 24, 2018
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    Also I think I wired the LEDs backwards, according to the text book power want to flow out from negative and I wires the positive of the LEDs to the power supply i think, I'll have to re check
     
  20. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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