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I bought a brand new Raspberry Pi. It came with a 5v ~ 1A power adaptor and a mini-usb cable. I plugged it in and plugged in my cat 5 into the ethernet port. The raspberry powered up but the Ethernet LEDs were not lighting up. After trying a lot of different things I decided to replace the mini-USB cable with a phone-charger cable. And it worked!! The ethernet LEDs came on. Mind you, I was still using the power adaptor that came with the Rasp Pi, I just replaced the Mini-USB cable. Can anyone tell me what was the issue here? Do mini-USB cables have varying power rating or grades? What did I miss here? Please help.

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Some possible issues:

  • You might be using a usb extension cable. USB looses power with range.

  • The power adapter might say 1A, but can be lower then the label says.

  • Try to disconnect so that both USB ports are available. If you have a usb-wifi dongle or something else that is consuming power, then you can have weird power issues.

Additional info:

  • You can get Micro USB adapters in a range from 0,5 to 2,1A. (Reference)

  • Model A ratings: 300mA. Model B ratings: 700mA. (Reference-A, Reference-B)

  • If you want a simple way of measuring how much power a USB device is using, you can buy THIS device with free shipping. (5,99USD)

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basically cable should not matter, most probably it will work fine if you switch cables back.

if it does not -- you have another working cable, use it. could be a bad contact issue or higher resistance of the old cable -- there are just too many different factors to speculate about.

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