Getting full 2.1 amp from a usb charger to power circuit

Hello, I have a micro-b breakout board to power my circuit:

Im currently using one of these, connected to a USB solar charger that boasts 5volts / 2.1 amps. Im assuming I just need to power my circuit from the VCC + GND lines, but it doesn’t seem to be getting much current at all. (300 milliamps @ 12V, after a step-up regulator, and power mosfet switch). I seem to get 600 ma at least when powering the circuit directly from a 5V power supply.

Do I need any type of digital negotiation before a USB charger will release its full 2.1 AMP?


What charger?
Why do you believe the advertising hype?

Not sure how that answers my question?

Whatever charger I state, will list 2.1 AMP / 5V in the specs.
If I go out and buy another charger from a different manufacturer with the same spec, I may still run into the same issue if Im not following some USB protocol.

Do you know whether or not I should be getting close to 2.1Amp as described, theoretically?


Most “USB chargers” are very simple power supplies and do not feature a protocol. They merely have an output that fits a USB style connector. Perhaps you are confusing a charger with the USB port on a computer, which does feature a protocol.

Unless you specify which particular charger you have in mind, it is not possible to answer your question.

Well, its this universal one: … ZrUqPlVhBc

But all of these solar chargers, even from specific manufacturers, do not contain more details then “5V/2.1 Amp” from everything I’ve seen.

So you’re saying, they generally should supply the full current with no protocol required?

In order to provide 5V, that device must have a step-up (most likely) or step-down voltage converter and the output current will depend on the capabilities of the converter. What is the load you are applying and how are you measuring the current? It could be that the regulator is overloaded and is partially shutting down.

The solar cell on that device is rather small and probably provides 1-2 watts. It will take several days of full sunlight to recharge the battery, if the full advertised 5V x 10 Ah capacity is realized.

BTW I’ve purchased some things from that turned out to be complete junk and quite useless.

Well, Ive charged (the solar charger) with an external USB charger for several hours until the solar charger indicated full, so I was hoping for near ideal test.
I am then delivering it through a 12v step up regulator ( input current up to 5A.
And then its switched with a power mosfet ( … 30N06L.pdf).

Its driving a 12v light bulb with its own current limiting.
I measure the current through the light bulb, as about 300 mA.

When I replace the solar charger portion, with a 5v power supply, I measure about 600 mA, so I conclude I should see at least that with the solar charger if its truthful.

However, at first my circuit employed a much smaller 12v step up regulator (input current to 1.4A), causing everything to blink randomly after a few seconds, and shut off the solar charger,
so I fear I may have damaged something in the process.

Just want to confirm I should be seeing more current before moving onto different components.

Thanks Jim.

By adding the 12 V step-up regulator you are adding a layer of complexity that could lead to an oscillating overload condition.

To test whether the solar charger meets the advertised claims, attach a 20 watt 2.5 ohm resistor directly to the output. The resistor will draw 2 amperes at 5 V and generate 10 watts of heat.

Note if, and for how many hours, the output voltage remains at 5V. The specs predict 5 hours, or about 10 ampere hours (Ah). For a slightly more fair test, you could also use a 5 ohm, 10 watt resistor, which should draw 1 ampere at 5 V for 10 hours.

Right, as I mentioned, I knew the 12V step-up regulator and mosfet would have an effect, but in the end, it seems a 5V wall adapter supplies 1.75 amps as input to my circuit, while the solar charger only delivers 0.7 amp.
I’ll try the resistor, but Im suspecting the solar charger is incapable of delivering the full 2.1 Amp for whatever reason.