You should not draw more than about 100mA from the USB ports.
In reality, it is more complicated than this.
I've taken two screenshots from the Device B schematic (released here):
Power in (fig A):
We can see that the 5 volt line (+5V0) is powered directly from the USB input power, through a 1.1A, 6V Polyfuse (miniSMD). I ...
My research began with the original thread on the Raspi forums: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=63&t=6050&p=291334&hilit=watts+power#p291334
To summarize what we've learned there, the total consumption of a Raspberry Pi is probably not more than:
4 W * 24 h = 96 Wh (I guess that's 346 kJ) (note this is an energy value, not ...
Power requirements of the Pi
The Foundation has recommendations for various models which range from 700mA to 3.0A.
These are quite generous, and all models will operate on a decent 1A supply - I can run my Pi3 with WiFi/keyboard/mouse/HDMI from an Apple 5W supply. Extra current may be required by USB peripherals and the recommended supplies make allowance ...
It seems that the only concern is that your power supply, if it's not a decent, reliable supply capable of 2A+ of clean output power, might not be able to power the Pi sufficiently, resulting in crashes or frequent rainbows.
All that max_usb_current=1 does is to set GPIO38 high, which in turn turns on a FET, which connects a second 39K ...
Everything for sale is built to a price.
Tha manufacturer wants to make a profit.
There is no need for many USB cables to carry more than a fraction of an amp so they would be built with thin wire. Thin wire is cheaper and lighter than slightly thicker wire. All other things being equal thinner wire has a higher resistance and can carry less current and ...
It only says 1.5Amp Total in the specs. It doesn't say how that current gets shared between ports, but most likely it's just simply connected in parallel, which means that you could draw 750 mA from each port, or 1.5 A from one port only. Or 1 A from one port and 0.5 A from the other. Any combination, as long as the total current doesn't exceed 1.5 A.
Cables do make a difference once you start to draw hundreds of mA or several A.
You can often tell how much current a cable can carry simply by its looks. Anything thick and stiff is good, thin and overly flexible may cause trouble. Check out these pictures to see what I'm talking about:
Cable length also has a similar effect: Shorter cables are much ...
Just noting that the rev 2.0 board no longer has the USB polyfuses, just the input 1.1A polyfuse. So the issues mentioned here should no longer be present in current generation Raspberry Pi boards.
These type of enclosed hard drives conform to the USB specification 2.0 specification, even though it's USB 3.0 it must be able to fall-back. USB 3.0 provides lots more power, but since it falls back it must conform to the USB 2.0 500 mA maximum current. The hard drive itself might use more power, but the built-in electronics will detect when to use ...
This is caused by inadequate power. Use a good power supply and a good
power cable. Some cheap cables that work with a cell phone, cannot
fully power the R-Pi. Some USB devices require a lot of power: most
will have a label showing the voltage and mA requirements. They should
be 5v 100mA each max, any more than this they must be used with a
A unit load is 150mA for USB 3.0, and without further configuration, it will only supply 150mA. USB 3 ports, however, can supply up to 900mA (or 6 unit loads) by requesting higher power. The current schematic does not allow for this, and so, the only way to this is to insert hardware between the Raspberry Pi and the USB 3 port to request higher current.
It's possible to power your RPi through your USB hub on two conditions:
the hub does not backfeed: this is easy to test; remove the SD card, connect the RPi's USB port (not micro USB port) to the hub. If the RPi's led doesn't come on the hub doesn't backfeed. If the hub does backfeed you can't use this hub with the RPi.
the power supply of the hub is ...
I guess that should not be a problem, for the USB device certainly not a problem. Depending on the USB implementation on the RPi it might not detect your device because it doesn't draw any current. If that is the case you can use a resistor to draw a little current on the USB output. (Put this resistor between the unused 5V and GND outputs on the USB ...
Good power supply is not enough. USB ports on RaspberryPi are behind polyfuses which limits current that can drawn from it to about 140mA (in practice, it should be even smaller). So no matter how good your power supply is, if your USB device wants more than say 120mA of power, it will fail. Note that USB specification says that enumerated device can take up ...
You can use my tool uhubctl, it supports Raspberry Pi model B+, 2B or 3B - these models have hardware ability to turn USB power off and on.
Use it like this:
Turn off power to all USB ports (must use port 2):
uhubctl -p 2 -a 0
Turn on power to all USB ports (must use port 2):
uhubctl -p 2 -a 1
Turn off power to Wifi+Ethernet (must use port 1):
there is nothing to handle, as the rpi will not drain more power than it consumes. if you intend to power something hungry from the rpi's usb ports (1.1A max) you may actually need a supply with some reserves. in addition, the board has a polyfuse that should prevent damage to the board on overvoltage conditions.
the rpi wiki has in-depth info on this topic....
Be aware that the USB port the Raspberry Pi uses for power does not have the data wires connected at all so the Pi cannot negotiate power requirements with the USB host and this can cause all kind of strange behavior. See this forum post in which Liz herself (foundation member) chimes in on this. Worst case scenario for you is the Pi works for a while then ...
I am running a Raspberry Pi2 with a 2TB Western Digital element hard disk mounted as root disk (apm set to 254 - effectively disabling standby) via a Y-connector.
Using a USB VA meter (eBay link - LCD USB Charger Current Voltage Detector Tester Monitor Meter For Phone Tablet) I measured (with both the USB HDD and Raspberry Pi2) 5V and about 0.7A.
It should be possible to run power over this distance, but you should use heavier gauge wire. CAT5 uses 24/26 AWG; a 50' loop of 26AWG would have a resistance of 4Ω; drawing 700mA would give a voltage drop of 2.8V - this would almost certainly cause problems.
The Pi should not be powered from it's own USB ports. It's not a safe way of supplying power. The correct way is to use either the micro USB port or the correct GPIO pins.
The hub you have is at fault here - it shouldn't be supplying power upstream along the data feed cable. You may have to take it apart and cut a wire.
Powering the Pi from two places is ...
The amp is the maximum current a charger can supply, not the amount drawn by the board. It does not make a difference if the board does not use all 2.1 amps, however it will make a difference if the board draws more than the charger can supply. And the pi can use more than the 700mA, say if you plug in stuff that draws on USB power, therefor more amps are ...
There are a few factors to consider here:
The power input to your Pi is probably through a wall adapter or PSU. You should check the rating of the adapter/PSU. If it is in the range of 1.5A to 2A, then your problem is partially solved.
Next in play, is the polyfuse and regulator on board the Pi. As per specifications on Adafruit, the B+ can handle upto 2A ...
The Pi 2 should be able to run that HDD directly. However, by default the power to USB is limited to 600 mA, which is not enough (I've had the same issue with an external drive).
To make 1.2 A available -- which is fine if your power supply is up to it -- add the following to /boot/config.txt:
And reboot. Your HDD should now light up ...
Popular things like the Raspberry Pi surround themselves with Urban Myths.
One such is the USB cable Myth.
That is not to say there is some grain of truth, there usually is, but people jump to conclusions.
USB2 is specified to supply 500mA max.
USB power is 5V ±0.25V
To remain in spec there should be less than 0.25V drop which corresponds to loop ...
This qualifies under category circuit rework.
The "best" solution, if the pads are still usable, is to purchase the replacement part and re-attach it. The part is about $1 USD but this does not include shipping Vendor Link (Part Number Found in Schematic)
It is generally a good idea to repair something to its original state. Most things can be repaired if ...
As far as I know, you can't.
But by using some very simple electronics you can. The most simple and straight forward option is to use 2 GPIO pins as input (one for each power supply).
Connect both power supplies (besides to their normal connection to actually supply the power) through some resistors (for safety and voltage level adjustment!!) to these GPIO ...
From my personal experience, WD Blue HDD (WD10JPVT/WD10JPVX with 0.55A average current) might work more or less reliably (== require about 1 reboot / month) connected directly to RPi without any powered hub.
Your particular HDD requires much higher currents, so it's very unlikely you'll be able to do anything reasonable without an external power.
It is acceptable to power the Pi via the GPIO pins, however to comply with the guidelines you should implement a power isolation circuit (as in the B+ or Pi 2 schematic). Direct connection bypasses the overvoltage protection but is acceptable with a well regulated supply (which most mobile chargers aren't).
According to the Raspberry Pi FAQ on Power requirements ( which can be found here --> https://www.raspberrypi.org/help/faqs/#powerReqs ):
Maximum draw from USB = 1.2A
Recommended Power Source = 2.5A
Now, according to USB specifications power output for USB works like this:
USB 1.x and 2.0 specifications provide a 5 V supply on a single wire