Powering this circuit off 3A USB charger, but it's only supplying 350mA

Question

I have a very simple circuit for a small RGB lamp I'm building. My plan was to power it off one of my many spare old USB phone chargers via micro-usb. It's just a string of 60 WS2812B LEDs with a NodeMCU as controller. I'm using a capacitor to smooth out the input power and resistor on the data line. In theory, the max draw from the LEDs is about 3.6A and the controller is somewhere around 200mA. With a 5V 3A phone charger, that should give me an acceptable amount of illumination from the LEDs while still suppling the controller enough power.

The issue I'm having is that my circuit is only getting around 350mA total. That's enough to run the controller and dimly light all the LEDs or have a few lit brightly. The brighter I set the LEDs, the more the voltage drops until the controller can't run. I've tried different chargers and different USB cables, but I seem to never get more than about 350-400mA. The circuit's really simple, so I'm guessing that's not the issue (showing it here in case I'm wrong about that). Is this an issue with the chargers limiting the current they send out? I know there are different ways the chargers 'advertise' their supply options, but I thought that was all on the supply side, not the draw side. Do I need to do something with the D+/D- pins to get the chargers to supply more current?

Answer 1

Under the assumption that the +5V line is coming straight out of the USB jack and nothing else is connected to this particular USB cable which connects to the charger: Power-negotiation may be a problem here. This means: The charger has somewhat like 500 mA as default limit and waits for a controller to signal a higher current draw. Use a 'as dumb as possible' charger to verify - but your chances are low, because these features are quested by the usb standard. At least afaik.

Furthermore, I would not mess with the D+/D- lines and USB at all - just use a fixed 5V wall adapater - all problems solved!

But, if you insist on using a Phone-Charger please have a look at this topic: What is the ideal way to handle data pins D+ and D- on a USB power adapter to be compatible with fast charging on devices? As you read you will see why 'messing with this stuff' is not worth the time.

Answer 2

After much debugging and ordering a 6A power supply I solved it. There are actually two different things going on here. The first is that my USB chargers don't want to deliver much power. My new 6A power supply solved that issue, but my circuit was still only pulling around 400mA. When connected to my bench power supply it pulled 2A, so that wasn't what I expected. I realized I had wired up the power a little different on the bench. Not connecting things differently, just in different places on the breadboard.

That was it. The breadboard was providing enough resistance to prevent the circuit from getting enough power. After shortening my connections as much as possible, the circuit was pulling 2A from my 6A supply. I've never dealt with more than a few mA on my own circuits before, so I didn't even think about resistance of the breadboard.

Out of curiosity, I wired up a 2A USB with short connections. It delivered 800mA (twice as much as it was), which isn't enough for this circuit, but it gives me hope that I'll find uses for all these chargers I have lying around.