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I have just ordered a pi 3 and a 5" backpack display with a few other things but I'm either supplying too much power or not enough the display draws 500mA through a micro USB cable I've plugged the damn thing into EVERY adapter in my house and used 4 different micro USB cables and no matter what the screen (with the hdmi cable connected to my pi) always shows white, black, pink, and yellow line things the display has only fully worked once and only very badly. So I was thinking would the USB ports on the pi supply enough power with an adjustable regulator attached? In short how much power will the USB ports supply?

P.S. There is no problem with the pi or display I know that much

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    I believe the most you can expect in total is 1200 mA, and you should be able to draw at least 500 mA from one port. So either one of the premises in your question is incorrect, you have hooked the display up incorrectly, or you do not have an appropriate 5V 2.5A power supply. – goldilocks Jul 21 '16 at 17:04
  • My first thought is to wonder about the software you are using to boot it. – SDsolar Dec 01 '16 at 20:10

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I believe the Pi3 can supply up to 1.5A total, certainly 1.2A. (I have actually tested over 1.2A.)

In practice this is rarely successful, because there are no standard power supplies which can power the Pi and deliver adequate voltage. This is often aggravated by woefully inadequate USB cables.

NOTE You cannot "supply too much power" - unless you use a non standard supply which has a higher voltage. There is a common misconception about the current rating of PSU. This is a MAXIMUM which the supply SHOULD be able to deliver at rated voltage.

The link https://raspberrypi.stackexchange.com/a/47642/8697 is a different scenario, but illustrates the issue. If you search this site you will find hundreds of similar issues.

You could measure the ACTUAL voltage supplied to your display, but there may still be transient problems (as with HDD). Try a powered hub.

Community
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Milliways
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  • I have found that the 2.5A power supply is best for multiple USB devices. Plus I have run a 2TB WD Essentials drive powered by the USB port. Note that the large (5TB) backup drives need their own power supplies. There are USB power monitors available - they show volts and ma on LED displays. – SDsolar Dec 01 '16 at 20:07
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You can check at USB standards at wiki, that USB can supply at max 500mA. regarding you display - try to work it out with external power supply to make sure it is a power issue.

Good Luck

guyd
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The documentation of Raspberry Pi clearly states that the USB ports are sourcing at least 100 mA and the maximum is 500 mA (standard USB 2.0 ports). The core board can consume to 1000 mA so you need a supply able to source (1000 + 500 * used_ports) / 0,75 mA, where the 0,75 factor is a safety factor: never try to push a power supply to his limit[*]. So if you connect a 2000 mA power supply you can connect only 1 to 2 devices that use 500 mA from USB ports, not more and depending to what does the RPi.

When playing with RPi or similar boards you need to have at hands a multimeter and a USB Pomer Meter / Charge Doctor: also the cheapest will give you valuable informations on the current flowing from the port. Without this informations troobleshooting is difficult.

So the first thing you need to do is to measure the Voltage between GND and 5V pins, with and without the display.

[*]: there are good quality supply that can withstand 100% current without problem but not all. If you are not a competent technician even let a safety limit.