Finding 3-Wire Strings in 2020

[i13]

You would experience the 50% brightness limitation with the 2-wire reverse-polarity strings. As the two channels are on the opposite polarity and you want them to both be on, the closest that you can get is to alternate the polarity very quickly and that's what you're doing. Each channel is quickly flashing on and off. The total light output from each channel is therefore 50% of what it would be if they were on continuously. The 3-wire strings allow both channels to be continuously turned on so they can be double the brightness compared to the 2-wire strings.

 

[MichaelF5]

hmmm strange, I have not noticed that, however I'm running the oscillation as fast as the mega can do it and just pump up the voltage on the transformer till I'm happy

 

[i13]

I have been analysing the wiring of each LED string, calculating the current that it should draw and modifying the string so that it draws this current at 31V. Another option is to adjust the voltage instead of modifying the LED string but I like the simplicity of having a common voltage for all of my traditional strings. Pixels are a different story and I have both 5V and 12V.

 

[David_AVD]

hmmm strange, I have not noticed that, however I'm running the oscillation as fast as the mega can do it and just pump up the voltage on the transformer till I'm happy

Exactly how fast is it running? The lower limit will be where you see flicker. The upper limit will be where the bridge driver output devices spend proportionately too long in their linear region. That could be the cause the heat. You only want to PWM (or reverse polarity) as fast as you need without noticing any flicker.

 

[MichaelF5]

Good question, I don't have a cro to check, guess I can add some delay until we see flicker then back it off

 

[David_AVD]

When I was playing with a 2-wire adapter a few years ago, I had each polarity on for 5ms. There was also a dead band time (when neither are on) of just 10us to make sure there was no issues at the switching point. So that makes it just 100Hz. You could go faster, but running into the KHz region is just going to cause issues.