LED grow light

Discussion in 'General Electronics Chat' started by matty204359, May 8, 2011.

  1. matty204359

    Thread Starter Member

    Apr 6, 2011
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    so I bought this led grow panel at the 2nd hand shop in town for 15 bucks. I found the same one on ebay for 80 bucks so I think its a expensive light. I took it apart and discovered what appears to be a large diode. This diode is on the red wire feeding the panel 12volts. what does this diode do and why is it getting so hot? how do I know if this thing is safe for 24 hour usage?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    You don't. We have had queries about this type of device from other people (one after it died). If someone tried to submit this design on this site his thread would be closed for safety reasons. Running LEDs off of mains is not safe, there is live high voltage all over it.

    It is a judgment call. I don't think it would catch fire, but I would be very nervous if it were around people. The fact that LEDs can be among the safest devices out there makes this gadget twice as obnoxious.

    Caveat Emptor, use at your own risk. If you want to make your own from scratch ask, they would be a good beginner project.

    Just curious, could you show a picture or point a link? I'd like to verify it is what I think it is.
     
  3. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
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    its got a DC 12volt 2.5 amps desktop adapter i just dont get the reason for the large diode 1N5401


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  4. tom66

    Senior Member

    May 9, 2009
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    That diode is clearly for reverse polarity protection; quite a good design in fact. If you reverse the polarity of the input by error, the lights won't illuminate, but at least it won't cause any damage. In theory LEDs could withstand reverse voltage but in practice their peak inverse voltage is usually very low and thus they could be damaged.

    If you know you are going to always get the polarity right, you can just remove it and wire the red straight in. The difference will be about 0.5V in supply and is unlikely to cause issues. The LEDs will be slightly brighter.
     
  5. matty204359

    Thread Starter Member

    Apr 6, 2011
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    The diode gets hot. I dont know if it is safe. if I diode burns out it wont catch on fire will it?
     
  6. cjdelphi

    New Member

    Mar 26, 2009
    272
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    use a higher wattage rated diode?
     
  7. tom66

    Senior Member

    May 9, 2009
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    Yeah, that's one part of the design which isn't good. It looks like a 3A diode for a 2.5A system.

    Diodes rarely catch fire but if that gets very hot it could fail open and leave you without a light. Or, it could fail closed unnoticed; it may have already done so. The diode may melt things if it gets too hot.

    You can replace it with a 5A diode which won't get as hot, or with a piece of wire.

    Diodes are rarely (if ever) rated in watts because their voltage drop and power dissipation is proportional to current. So you might have a 1A diode, and a 3A diode, but never(?) a "3W diode".
     
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  8. Markd77

    Senior Member

    Sep 7, 2009
    2,803
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    It's a funny looking PCB. All the round areas of copper could be replaced by square fills. Also the (surface mounted) through hole resistors are probably there because they are for lower voltage LEDs and need higher power rating, but it would make more sense to me to use a couple of parallel surface mount resistors or use strings of more than 3 LEDs for those ones.
     
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  9. Wendy

    Moderator

    Mar 24, 2008
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    The fact it uses DC makes me a lot more comfortable. Components like diodes don't generally catch on fire, though they crisp their neighbors. I figure this part is dissipating around 3 watts max. You could replace it if you want, but it is probably OK as is.
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    Matty, Where are you located?
     
  11. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
    3
    Windsor Ontario Canada.
     
    Last edited: May 9, 2011
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    It helps to know where you are located for sourcing parts.
     
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  13. matty204359

    Thread Starter Member

    Apr 6, 2011
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    thanks I updated that in my profile so it will show up on my posts
     
  14. vladtess

    Member

    Jan 5, 2011
    43
    1
    You got some nice camera, my would never be able to do such a close focused shot.
     
  15. matty204359

    Thread Starter Member

    Apr 6, 2011
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    I know eh. and those are the lower quality pictures because I had to compress them to JPEG for the attaching them to the post. I didn't think any body would want to download a HUGE zip file.
     
  16. iONic

    AAC Fanatic!

    Nov 16, 2007
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    240 LED's, wow! Would not want to build this by hand, nearly 500 solder connections!
     
  17. matty204359

    Thread Starter Member

    Apr 6, 2011
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    for 15 bucks it was a steal.
     
  18. matty204359

    Thread Starter Member

    Apr 6, 2011
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    actually its 400 leds(25 rows of 16). 336 red(21 rows) and 64 blue(4 rows) for 15 bucks it was a steal.
     
  19. strantor

    AAC Fanatic!

    Oct 3, 2010
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    If the diode goes, it will just make a little crackly sound and let some smoke out. then there won't be any light.
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    The diodes are cheap. I'd probably use a schottky type to replace them, since a silicon diode drops around 1V, and a schottky less than half of that. It would run cooler.
     
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