Portable battery sources and power consumption

I’m making a light painting wand and will be using it with a battery pack. I have some questions regarding power draw.

What happens in the these 2 different scenarios if my pattern/brightness draws more amps than my power source can handle? I will likely power it with a 5v 2.4amp usb rechargeable battery

Scenario 1: connecting the power to the strip with a barrel connector

Scenario 2: connecting the power to PixelBlaze with the micro usb connector

If the result is just less brightness, without damaging anything then I’m fine with that. However, on the other hand, if by doing so, I risk damaging components, then I’ll be more cautious in designing my patterns to make sure they don’t pull more power than the given scenario can handle.


I remember from your other post you said your strip has 123 LEDs, right? One other thing to check is if your rechagable USB battery is rated for 2.4 AH (amp-hours - a measure of total power storage capacity), or your pack, connectors and cables are rated for 2.4A max. The rest of my post assumes the latter.

I always found this post useful for these kind of estimations.

Most strips pull 20 ma per pixel per color. If yours is typical, then an all-white image would be 123 * 60 ma = 7.4A, which is over both your supply and the 1.8 amp rating of the micro USB connector.

Most patterns average more like 20 ma per pixel, so that gets you down to 2.46A - now you’re within striking distance of your 2.4A USB pack, and it would be a good idea to switch to using a barrel connector.

You can protect yourself effectively by using the “Limit brightness” setting on the Settings tab.

In practice, I’ve overdrawn the micro USB connector on Pixelblaze several times by accident. Nothing smoked (which is laudable - I smoked several PB v1s), but the board tends to reboot and I don’t think it’d be good to plan for that to happen regularly :slight_smile:

Thanks for the reply. Yes I’m the 123 led guy ;). If using the barrel jack, and I the pattern wants too many amps, will that damage the leds, or just make them dim? Also, per Wizard, I was able to measure amps with my multimeter, so now I can test the power consumption accurately. I was just more worried if for some reason I accidentally used a pattern that required too many amps. Didn’t want to damage the hardware. Thanks

For 123 LEDs / 7A, If using the barrel jacks, I’d be mostly thinking about overloading your USB pack’s 5V regulator. Hopefully it has overload protection, which would also protect the USB connector on the pack not being rated for that much current. I’m not as worried about sufficient wire gauge or the traces on the strip.

I’ll note that most USB charging cables are rated for 1.5A, and even ones specifically for power delivery go up to 5A, but I don’t think you’ll be able to draw 7A from your pack’s regulator long enough to heat the cable up.

So in this scenario, while the voltage might dip enough to reset the Pixelblaze board, I don’t think you’ll harm it or the LEDs.

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