Ever wondered what's in your cheap Chinese led?

[spoon]

So a few years ago my  trusted  cheap  Chinese led  unit  dropped a channel  so  I decided  to  investigate it and pull it  apart.

It  came  apart  easily  with  about  8 screws  removed I was  greeted  by  two  half  as per  photos  below,  the  first  half  consisted  of  3 cooling  fans; overly  noisy and running  on 12v, the  fan power  supply and 4 drivers  from  memory  they  were  rated  80-130v at 300ma and the  4 channels were  controlled by  2 simple  on off  switches  each  operating two  drivers  (channels) of the  same  colour  either  blue  or  white. A common  modification  for  these  type  of units  is to  add a resistor  or fan speed  controller  to  trim the  fan speed  back making  the  fans  quieter,  I never  bothered as my  overflow  box  weir  at the time was  noisier anyway. 

The  second  half  consisted  of wires  going  to  the  drivers,  heatsink  plate  and leds. If you  notice  in photos  the  heatsink  plate  is very  thin  and has  no  fins  this is a cost  cutting  method  as the  LEDs  are  underdriven  at 300ma  rather  than  the  350ma epistar  LEDs  are  designed for.  This  has  the  fortunate  effect  of increasing  the  life  of LEDs  by  reducing  heat.  This  also  means the  LEDs  are  no  longer  1w LEDs more  like  0.8w and can  have  an effect  on the  spectrum  of light  being  output ( not  really  an issue  here  as they  grew  coral  fine anyway,  but  a consideration for more  advanced  builds) the  light  is meant  to  be using  120 w of power  but  has  only  112 "1w" LEDs  so  theoretically  it's  only  about  as good  as 90-100 1w LEDs  being  properly  driven  at  350ma. The  rest  of the  power  is used  by  fans and heat losses.  

Also  of note  looking  at  photo  of pcb with  LEDs on it  is the  colour of LEDs ,  the  yellow ones  being  the  white  colour, clear  being  blue and brownish  ones  being  uv(on blue  channels).  The  white  ones  are  coloured  yellow  due  to  a Yellow  phosphor  coating,  they  are  actually  blue  underneath  and the  blue  light  excites  the  phosphor into  emitting  white  light.  Interesting  to  note  there  is no  such  thing  as  a true  white  led,  they  are  all  either phosphor coated  blues  like  this (thicker  orange phosphor  coating for  warm white) or made  up  of a combination of red, green and blue  LEDs tightly clustered  on the  same  chip to  mix  together  and give  out  white  light. 

The  uv  LEDs are  something  I recommend people  avoid  with  cheaper LEDs  as these  epistar  uv  LEDs  don't  last  long.  The  brown  colour  is where  the  uv  light  has  broken  down  the  epoxy  protecting  the  led. 

At  this  point  I wanted  to  diagnose  Wether  the  faulty  channel  was  an led  fault  or driver  fault so  I  unplugged  and swapped  over  the  driver  from  the  faulty circuit  to one  from  a good  circuit (these  just  have  small  leads  that  unclip)  as it still  didn't  work  I knew  it  was  an led  problem  and not a driver.  

Then came  the  next  task,  removing  around  120 very  tiny  screws  that  attached  the  pcb/LEDs  to  the  heat  sink  plate,  took  a very  long time ,...  So so  fiddly.  I then  tested  each  led  individually with  very  old  batteries from  a small  flash light  til  I came across  the  faulty one.  The  112 LEDs  in this  light  are  arranged  in four  circuits  each  with  27  LEDs in series  .  If one  led  in the  27  goes  all go.  This is  what  happened  here. I removed  this  faulty  led and bridged it temporarily with  a small  piece of wired soldered across,  knowing  that  the  other LEDs  could  safely handle the  small  increase  in voltage  until replacement LEDs arrived.  

I ordered replacement epistar  LEDs  from  eBay,  less  than $1 each and also  ordered  enough  to  replace  the  uv ones. After  painstakingly removing  the 120 odd tiny  screwed  I had  carefully put  back  in a few weeks earlier,  I then  soldered in the  new  LEDs.  It's small  and fiddly desoldering and resoldering  these  units and you  have  to  be  careful  to  do  a good  job  as you  don't  want  to  be  pulling  those  tiny  screws  out  again  to  repair  a dry  solder  joint  in a few  months. Repairs  all  done  and worked  well until  about  a year  later  and a power  surge  destroyed all  the  drivers.  I managed  to  buy  another  unit  the  same  cheap from  another  local reef keeper which  had  one  channel  that  flashed all  the  time.  Was  fine  for  keeping  my  corals  alive for  a few  weeks  until  the  flashing  drove  me  nuts  and I had  this  unit  apart  too.  Using  the  same  process  I discovered it  was  a driver  at  fault. My electrical knowledge  doesn't  extend  far enough  to  repair  a driver  so  I decided  to  replace it.  After  an hour  searching I found  the  exact driver on dhgate.com for  $14.  When  it arrived simply  plugged  it  in and and I was  good to  go. 

It's  good knowing  what  you are  buying  when  it  comes  to  cheaper LEDs  and all  of the  cheap Chinese led  units  I've  seen  use  the  same  tricks  to  reduce  cost  or increase  lifespan regardless  of whether  they use  1w or 3w LEDs so  it's  worth  looking into  how  they  work  and how  much  of the  claimed  wattage  is actually available  to  the  LEDs. The  quality  of heatsink  vary  a lot  too,  some  actually  have  decently  thick  finned  types. 

The  unit  eventually  started  to  rust  and I started  a project light  to  try  get  the  best  of led  and metal halide....  New  thread  soon

[fishyNZ]

It is called Duty Cycle and it is not only the Chinese that uses these "tricks".

I have been involved in designing display interfaces requiring LED lighting; by setting a specific duty cycle, a target power consumption can be achieved (e.g. battery applications), as well as simpler product design (drivers requiring smaller or no heatsink).  Brightness levels can also be adjusted, if required, by varying the duty cycle (pulse-width modulation).  

I believe cost is always a consideration, no matter which part of the world a product is designed.

[spoon]

Yes very true,  my point  for  mentioning the  "tricks"   is the  average consumer  has  no  idea  they  aren't  getting 120w at  the  LEDs. 

[fishyNZ]

Isn't lumens more important than wattage, for lighting applications such as fish tanks?

Edited May 6, 2016 by fishyNZ

[spoon]

Yep but  even more important is par.  Spectral  difference from  different bin  number LEDs  can also  make  a difference.  Many  of the  higher end LEDs  are  built  with  this  in mind. These  cheapies  are  just  about  bang for  buck.  I would  say  values  would  vary  wildly.   wouldn't have  a clue of the  output  of my  lights  in par only that  they  work well  enough for  my  application but  just  have  reliability issues.  

[alexyay]

As Spoon has said, I believe PAR is more important than Lumens. Lumens are what the human eye can see, whereas PAR is more relevant to plants. I personally look at PAR, Wavelengths and Wattage (to an extent) when looking for LED lights