Power Teensy through USB charger

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tuzzer

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I have read about the three options of powering Teensy 3.1 from external power. One involves cutting a pad, another one involves cutting a wire in the USB cable, and another one involves adding diode.
I am wondering why it isn't possible to simply supply power through the USB port without the computer. I want to do this because I will need to make many of the device that I am making. Therefore, I am trying to figure out a way to power the Teensy externally without making any modification to the board.

I have a one of those phone charger that plugs in to the wall with a USB port. I programmed my Teensy to simply turn on an LED. I have an USB cable connected to my Teensy 3.1. It turns on on its own when I plug the USB cable into my computer's USB port, but it does nothing when I plug it into the USB port on my phone charger. Why is that?
I measured the voltage at the pin vin and pin 3.3v, they measured 4.8V and 3.3V respectively. Why won't work?? Is there something wrong with my USB charger?
 
It depends on the specific charger. Many try to be 'smart' and provide appropriate power for a given phone by measuring the resistances in the data pins, and the Teensy won't be recognized. I don't use Apple products, but often it seems to be mentioned that official Apple chargers do this. Perhaps other chargers do this as well. I've had it work on the various chargers I have around the house for Android devices (Samsung phones, Kindles, plus random chargers I've bought over the years).

Now, you probably can't expect more than 100mA of power from a charger, which I believe is what the USB spec. calls for. So, if you are powering lots of neopixels or servos, you might need something with more current.

Another problem comes up if you attempt to use batteries that are meant to charge phones when you are away from a plug. Many of these batteries will turn themselves off if there isn't enough of a power draw. Paul S. in fact ran into this, and came up with a circuit that you can build, that plugs into a second USB port, that was enough to keep the battery from going to sleep, and didn't drain the battery too fast: http://www.dorkbotpdx.org/blog/paul/battery_pack_load
 
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To clarify -- 100 mA is the minimum current a USB charger should supply. If a USB load needs more current, it sets the resistances on the data pins (or a 3rd ID pin), to inform the charger over to supply more current. There are other ways to 'negotiate' more current over the USB link. Most cheap chargers don't do this -- they just supply up to 500 mA without complaining.

The Teensy 3 draws < 100 mA, and should work without problems. Perhaps there is something non-standard about the USB charger you are using ? Try a cheaper one (it'll be less picky about what it is connected to).
 
Jp3141 said:
To clarify -- 100 mA is the minimum current a USB charger should supply. If a USB load needs more current, it sets the resistances on the data pins (or a 3rd ID pin), to inform the charger over to supply more current. There are other ways to 'negotiate' more current over the USB link. Most cheap chargers don't do this -- they just supply up to 500 mA without complaining.
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Yes, but as far as I know, the Teensy does not ask for a higher power amount via the data pins, so you need to plan on getting only 100 mA if you are running from a random USB plug.

Jp3141 said:
The Teensy 3 draws < 100 mA, and should work without problems. Perhaps there is something non-standard about the USB charger you are using ? Try a cheaper one (it'll be less picky about what it is connected to).
Click to expand...
It depends on what else the Teensy is running. For example, if you are driving lots of neopixels or motors, it can ramp up the power requirements.
 
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