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mdf

mdf

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#280693 3-Jan-2021 22:31
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I'm making a big clock:

 

 

I was very pleased with myself; all the code and temporary wiring worked. But Issues Arose when I was starting to close things up and make permanent connections. I think I've sorted it out but am curious as to whether I am on the right track as to why the issue happened.

 

Basically this is a very long strip of RGB LEDs. By the end of the strip, I was having colour fade issues that were especially noticeable on white colours. Some research led me to voltage drops and recommendations to add additional +5V and grounds at multiple places along the strip. Tested with alligator clips and the intended power supply (large USB powerbank) and +5V and ground at either end and one in the middle worked really well. Lit up all digits nicely, no colour fade.

 

Ran permanent soldered connections: issues started. Lights would blink three times and then go out. After lots of trouble shooting I eventually diagnosed that:

 

  • battery --> digits + bright white = issues
  • battery --> digits + any other colour (i.e. non-white) = okay
  • battery --> alligator clips --> digits + bright white = okay

As I understand it, on RGB strips white = all three colour chips on so potentially three times the current draw. I am guessing that this tripped some kind of current limiting safety feature (I suspect on the battery).

 

What confuses me though is why there aren't any issues if using the alligator clips with otherwise the same set up. Are the alligator clips perhaps acting as just big enough of a resistor to bring the current down under a limit?


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Batman
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  #2629941 3-Jan-2021 22:46
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yeah when you start messing around with time machines the world does tend to get a bit weird ...

 

good luck hope your time machine succeeds!




axxaa
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  #2629943 3-Jan-2021 22:57
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Yes I suspect the alligator clips have a higher resistance then the soldered connections. You need to add a series resistance to stop overdriving the LED's


geocom
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  #2629944 3-Jan-2021 23:05
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You will be drawing a lot of current by my count you have a total of 226(8 LED's per segment * 7 Segments per digit * 4 Digits + 2 LED's in the middle) LED's the allowance you should give yourself for the LEDs at full brightness is 60mA given that you should be drawing a max of 13.56A.





Geoff E




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  #2630135 4-Jan-2021 11:10
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If its that lead at the bottom of the picture, there are some terrible really high resistance ones around. I have one that I can put directly across my 12v power supply, and it doesnt even cause it to change to constant current mode, just 3 amps or so into a lead that starts to get very hot and smelly.

 

 





Richard rich.ms

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