Failure Of RED Colour on Dumb RGB strips

[tonylights]

This year, ( christmas 2013 ), I have had a large number of the Dumb RGB strips fail , where random blocks of three lights just stop illuminating along the length of the strip - I used the strips cut to 3 Meter lengths as Wall Wash onto the front of the House. But the odd thing is that on all occasions it is only the RED colour that does not work - the GREEN and the BLUE continue to work properly. I don't know if it is a "dud " batch of lights I have received from Ray or whether is due to something related to how I have set up my Wall Wash ?
Does anyone have any thoughts - I'd really appreciate any suggestions.

 

[DrNeutron]

I used dumb RGB quite a bit this past Christmas and have had zero issues in regard to failures with the exception of water ingress at one point (my fault). I would suggest taking a strip and applying 12v to V+ (if strip is 12V), and then touch each contact on the strip to see if you get red, green, blue. This would eliminate any hardware issue. I always test each strip I get from Ray before cutting and mounting (actually found one that was marked RGB, but was wired GRB)....Try it at each end of the strip also.....

 

[David_AVD]

Do you have a link to the strip used?

 

[fasteddy]

What may be happening is that the red colour may be failing due to possibly incorrect resistor size to drive the red coloured LED. Typically the red runs at around 2.1 volts per LED where as the green and blue can run around the 3.1 volts range. When the LEDs are put into series then the voltage is added for each LED in series, so for Red it would be around 6.3 volts and for green and blue is would be around 9.3 volts, So as you can see the red uses a lower voltage than what the other 2 colours need, so if the resistors are all the same value for all 3 colours then that would be a reason for your failures.

 

[fasteddy]

Further to that someone over at LOR did a close look at their strip and found the Red resistance value to be 240 Ohms

My calculation put the resistor value for the red if using a forward voltage of 2.3 volts per LED and 18.5mA output from the 2811 as being a value of approx 330ohm The reistor value for the green and blue if the forward voltage is 3.2 volts would be approx 150 ohms. So looking at this it appears the Red resistor value is actually too low and this may be the reason for the reds mainly failing. Worth a check to see what the resistor values are on your strip.

So maybe look at lowering the voltage slighty if possible as this may help with giving longer life to the reds,

 

[tonylights]

thanks for all your comments - you've given me a few things to follow up on. regards, Tony

 

[Madko]

I also had a similar problem with my dumb strip used for wall washing this year.
I found that I could only produce red and yellow??? Which didn't make sense to me. On further investigation, I found that when I un-soldered the strip to make 2 meter lengths the solder actually join 2 of the colours together at the solder point. So when I was activating a certain colour in my sequence then 2 colours were being activated.
Cleaned up and fixed.


Maybe something simple?