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But if that is the case, why did the designers of RPi remove the polyfuse in Model B? I thought that was an admission of design mistake.tonyhughes wrote:All the discussions I have seen revolve around the opinion that beyond 140mA you are going to have problems...
I read it somewhere in an interview in one of the MagPi magazine issues. Maybe I remembered incorrectly. But the fact remains that the polyfuse was removed from USB.tonyhughes wrote:Where has that been stated?
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If the RPi Rev2 model B is powered via the micro USB power connector then all current from the power supply passes though the main polyfuse F3.helpme wrote:Model B has no polyfuse that limits current that can be drawn from USB port to 140mA. So, what is the new maximum current that can be drawn from the USB port of RPi Model B?
F3 has a 750mA 'hold current' rating. If you go above that then the system will be unreliable... USB devices stop working... SD corruption.... RPi reboots etc. Of course currents above the 'trip rating' of about 1A will totally shut the RPi down within a few seconds.
The RPi itself (Model B) uses about 400mA or so. Mouse and keyboard use another 150mA or so. What's leftover is available to the USB ports and GPIO 5V pins.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.
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The command "usb-devices" reports, as "MxPwr" what appears to be the maximum current requirement for a given USB device (eg. see http://www.cpmspectrepi.webspace.virgin ... erReq.html) which, as far as I have been able to determine, by monitoring a Pi's current, with or without a device plugged in, a "fairly good guide value".
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, 2xB2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, and a A+) but Buster on the P4B's & P400. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm