{"id":278,"date":"2019-09-04T18:19:11","date_gmt":"2019-09-04T17:19:11","guid":{"rendered":"https:\/\/ca.rstenpresser.de\/blag\/?p=278"},"modified":"2019-09-04T18:19:11","modified_gmt":"2019-09-04T17:19:11","slug":"el-cheapo-china-dmx-led-spots","status":"publish","type":"post","link":"https:\/\/ca.rstenpresser.de\/blag\/2019\/09\/el-cheapo-china-dmx-led-spots\/","title":{"rendered":"El-cheapo China DMX LED Spots"},"content":{"rendered":"

I recently got me a set of 4 DMX-Controllable LED Lights of ebay for 35\u20ac including shipping.<\/p>\n

\"ebay-listing<\/a>
ebay-listing picture<\/figcaption><\/figure>\n

But they are rather dimm. The article page states<\/p>\n

Power Consumption: 15W
\nLED: 12 pcs * 1W LED (Red*3, Green*3, Blue*3, White*3)<\/p><\/blockquote>\n

So, lets open one up and check the insides.\"insides<\/a><\/p>\n

When setting all LEDs to maximum (RGBW) the multimeter reads 185mA DC. At just 12V thats not barely enough. Interestingly though, setting it to AC+DC mode reveals a stunning consumption of 340mA, thats almost 4Watt.<\/p>\n

But wait, why is there even AC voltage when everything is turned up to full brightness?<\/p>\n

Scope to the rescue!<\/h2>\n

I put a 1Ohm resistor in series to measure current, so 1mV -> 1mA. The voltage across the LEDs is always 12V, as output by the PSU.<\/p>\n

\"\"<\/a>
scope showing the current waveform for the blue led<\/figcaption><\/figure>\n

You can see 478us PWM-Period with a on-time of 126us. Thats a DutyCycle of 26% at 100% brightness. That explains the AC current measured earlier. The peak current is ~275mA.<\/p>\n

    \n
  • Red: 780mA, DutyCycle 17us\/318us -> 0.5Watt RMS<\/li>\n
  • Green: 350mA, DutyCycle 108us\/480us -> 0.95 Watt RMS<\/li>\n
  • Blue: 275mA, DutyCycle 126us\/480us -> 0.86 Watt RMS<\/li>\n
  • White: 487mA, DutyCycle 98us\/480us -> 1.19 Watt RMS<\/li>\n<\/ul>\n

    This roughly correlates with the 4Watts measured with the multimeter.<\/p>\n

    But what about the overall quality? I guess you get what you pay for.<\/h2>\n
      \n
    • The LED PCB is made out of aluminium and is a decent heatsink. But it is rather thin. The LED-lenses are as described and work properly.<\/li>\n
    • Plastic case seems nice. No problems here<\/li>\n
    • The Control-Knobs are easy to use, the 7-Segment-Display shuts off after a few seconds. Premium feature!<\/li>\n
    • No gamma adjustment. 50% Brightness equals 50% (of max) DutyCycle.<\/li>\n
    • The DMX In- Out-Port are just connected to each other. No RS485-driver to improve signal quality<\/li>\n
    • The internal plugs are JST-XH (clones?), but they saved a few cents by just populating pins instead of complete receptables on the controller board.<\/li>\n
    • The PWM-Base-Frequency of red is different than the other colors. WTF?<\/li>\n
    • Since no DC is > 25% one would expect that the PWM-Periods are interleaved so the current does not add up. But nope, thats not the case.<\/li>\n
    • No resistors in front of the LEDs. So the 3 red LEDs which have a combined Vf lower than 9V are run at the full 12V.<\/li>\n
    • There is no sign of any PFC on the primary side of the PSU.<\/li>\n
    • The PSUs isolation between primary and secondary is garbage. The feedback-opto has all its 4 terminals pretty close to the primary side. Thats less than 1mm.<\/li>\n<\/ul>\n\n\t\t