RGB 12mm Modules from Ray Wu

[Nath_From_NT]

Guys,


My head is hurting from all this watts and volts business and I need some clarification.


I'm looking at some of these http://www.aliexpress.com/fm-store/701799/209889132-314089657/12mm-diameter-Through-hole-LED-channel-letter-DC5V-input-RGB-waterproof-0-3W-120degree-beam-angle.html


150 of them in fact for a mini tree or 10.


My question is this, 150 of them @ 0.3watts each is 0.06amps each which is 9amps for a whole tree? Yes? Or am I looking at this wrong? 9 amps seems like a lot and I have no idea how I'd power it all if I'm right.


Thanks all,


Nathan

 

[fasteddy]

So the maths would be

0.3 watts x 150 pixels = 45 watts so not much at all.

Remember its a matter of Ohms law, the lower the voltage the higher the current for the same amount of wattage used

So current (I) = Power (P) / Voltage (E)

so ill do a comaprison of a 12 volt and a 5 volt light using the same power

0.3watts / 5 volts = 0.06 amps

0.3watts / 12 volts = 0.025 amps

This is the reason when using 5vdc lighting to ensure you have a large enough cable to handle the current that will be drawn.

This is one of the main reasons i personally prefer using 12vdc lighting and using 12vdc RGB strips and modules over 5vdc strings, plus voltage drop is less of an issue.

 

[lithgowlights]

Dont forget that unlike pixels, these are simply an RGB LED with 3 resistors across a 5V or 12V supply, with the excess voltage being dropped by an appropriately sized resistor, so they will draw roughly 20mA per color per LED at both 12V and 5V. While the actual wattage at the led might be 0.3W, there will be additional power dissipated in that resistor, more so at the higher voltages

I run 100 of these at 5V in my minitree, and they draw a bit over 1A per color, but only 2.5A when white, but this is due to the voltage drop in the 3m cable leading to (and back from) the led's, the 5 meter LED cable from the feed point out to the end.

It did not make a huge difference if I fed from one end or both, with less than 0.15A increase in current for the 2 strings, so I chose the center feed only so they are all the same brightness and color when driven to 100%

 

[Nath_From_NT]

I run 100 of these at 5V in my minitree, and they draw a bit over 1A per color, but only 2.5A when white, but this is due to the voltage drop in the 3m cable leading to (and back from) the led's, the 5 meter LED cable from the feed point out to the end.

I don't think I get it Lithgow. Your trees with 100 LEDS only draw 2.5 amps total, per tree all on white? If that's the case, I can make loads more! My maths must be bad.


What do you mean by the "the 3m cable leading to (and back from) the led's" You have two cables?

It did not make a huge difference if I fed from one end or both, with less than 0.15A increase in current for the 2 strings, so I chose the center feed only so they are all the same brightness and color when driven to 100%

So you feed power into each tree at the 50th LED? Is there any way I could piggy back power from each tree to the next with a T connection?