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Raspberry Pi not powering up with mini USB

by alexcharlton on Thu Dec 20, 2012 3:42 pm


I bought a mini USB wifi dongle from adafruit to go with my Raspberry Pi B. The Pi works just fine without the dongle plugged in, but it won't power up (or it will shut off) whenever the dongle is attached. I figured this was an issue with the dongle drawing too much current, so I purchased one of your Pi-supported power supplies. It seems to have made a slight difference, but in the end the Pi still cannot run with the USB dongle plugged in. No other devices have been attached while testing this.

Since both the dongle and the power supply are endorsed by you, I assume that this is not the standard behaviour for these parts. Any ideas about what could be going wrong?

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Re: Raspberry Pi not powering up with mini USB

by adafruit on Mon Dec 24, 2012 12:33 pm

you may have to go with a powered hub - most pi's dont mind having the USB wifi dongle plugged in but its not 'supposed' to work
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Re: Raspberry Pi not powering up with mini USB

by Lob0426 on Tue Jan 01, 2013 12:58 am

Whether you can get a WiFi adapter to work directly plugged into a RasPi or not depends a lot upon the version of board you have, And how good your power supply is.

version 1.0: 140ma polyfuses at the USB F1 and F2. Many problems with devices that drew over 100ma. Also had problems with polyfuses that were out of spec, too high of resistance. Direct use of WiFi without modification not very successful. WiFi draw to high.

version 1.1: 0ohm resistors replaced the polyfuses. A stop gap board before the revision. I believe D14 was removed at the HDMI also. Usually successful with WiFi

version 2.0: polyfuse/resistor pads removed, Has "mounting" holes, fixed a number of problems including the 1v8 issue where the regulator in the LAN9512 was being used rather than the 1v8 on the board. This caused overheating of the LAN9512 "chip". Usually successful with WiFi.

Overall the version 2.0 boards are the most forgiving. Can be back-powered through USB ports without modification. The ver 1.1 also can be back-powered.

Usually successful with WiFi means; If the Wifi does not draw too much power it will usually work.

Remember that F3 is only 750ma. You can usually draw up to 1A against it with no major problems. You also would need to have at least a 1A power supply. The RasPi draws just under 400ma at idle with nothing attached. All of these limitations mean it is much easier to have WiFi with a powered hub. I can use a WiFi on a couple of my boards because 1 board has a 1.1A polyfuse in place of F3. The Other is Back-powered so it does not go through F3.
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