Maximum power draw and using separate power source

System48

I'll be getting my tape tomorrow and wanted to check something before I fry a USB port. On the product page on Adafruit it list the power draw at 300ma for a typical pattern but I can't seem to find a clear spec on the max power draw. If the tape is using the neoflex 60/m strip that would be 60ma per LED at full white and 3.6A for the full 1 meter strip. I am planing on using these for PC lighting and there is the potential for it to be at max power for more than a few seconds.

With all of that said, I had read an earlier post with someone asking if an additional strip could be added to the end and the answer was yes with the caveat that it be powered separately and only the data connected. Given that solution would it be a better option to separate the strip after the controller and power it directly from my power supply?

Matt Mets

The trick here is that the LEDs are limited in brightness to about 30% of their power. They should draw something like ~600mA at full brightness, if you don't modify the firmware running on the strip. The spec is technically 500mA, however we've only seen issues with known weak USB supplies, like the original RaspberryPis (and those can be avoided by using a USB hub). Recent RasPis seem to work fine.

Since it's open source, though, it's possible to remove that limitation and use the maximum brightness of the LEDs. They are WS2812b type LEDs, and will draw around 2.5A at maximum brightness, so if you need extra brightness you could modify it to run on external power first.

System48

Thanks Matt. Due to an issue I ran into during programming I decided to use the USB port from my motherboards rear I/O. I was going to use an internal header but in case I screw something up in programming and need to reset it, it will be a lot easier if i can just get to it from the outside.

I do have one question concerning wiring with an external power source. I am intending to leave the USB connected to the system and have the power wired separately from 5V off my PSU to the LED strip. Since ground is common in the entire system would I connect just the 5V from the PSU cable and the ground path goes through to the USB port?

One other thing, I didn't realize that there was a button on the controller. I ended up discovering after messing around with one of the example Arduino programs and loading a bad program. What I discovered is that if you hold the button down while you plug it in a default firmware, device manager showed bootloader in the name, is loaded up for a few seconds. Which seemed like the behavior described using the two needles to reset it. I was able to get the factory program uploaded after a couple tries to get the timing right and everything was back to normal.

Matt Mets

It's probably best to run a ground wire too, to be safe- the ground connections on the USB header might not be beefy enough for the return current.

Yeah- the button is probably not documented well enough! The bootloader feature wasn't included on the first production of BlinkyTapes (they have a black button), but for all later productions (with a white button), holding down the button when applying power causes the blinkytape to stay in bootloader mode for a little while, to act as a replacement for the needle reset trick. Really need to add that to the troubleshooting page :-/.