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I recently started building out a combination NAS and HTPC on a Raspberry Pi and came across some interesting information about powering Raspberry Pi’s. While this isn’t a project post per se, I thought it was interesting enough to share and wanted to send this out as sort of a PSA for the users out there who don’t know the potential danger of “backpowering” a Raspberry Pi.

For those who don’t already have one, here are a few suggestions for where to get a Raspberry Pi.

Where to get a Raspberry Pi

If you have some of the peripherals (SD card, HDMI cable, micro USB power supply), you can get started with a standalone Model B Raspberry Pi for as low as $35.

If you would rather get a starter kit, the prices are pretty reasonable and usually includes an SD card pre-loaded with the Raspberry Pi New Out Of Box Software (NOOBS). Here are two good starter kits.

Power Consumption

As an Arduino die hard, I didn’t think I really needed a Raspberry Pi for anything. I was sold once I realized I could run all of my home web server functions on the 3.5 watt ARM processor instead of 85 watt Intel chip in my desktop. The Raspberry Pi will actually pay for itself in about 4 months.

Utility cost of running home server on full x86 desktop (Intel dual core, ATI Radeon HD GPU, 3 HDDs) [high estimate]

(Power draw x hours per week x weeks per year x cost per kilowatt hour) / (1000 watts per kW x 0.85 efficiency x 12 months a year) = estimated cost per month

(150 watts x 168 hours x 52 weeks x $0.10 per kW hour) / 1000 watts per kW x 0.85 efficiency x 12 months a year) = $12.85 per month

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Utility cost of running home server on Raspberry Pi and one external hard drive (5 watts for Raspberry Pi, 15 watts for HDD under load) [high estimate]

(20 watts x 168 hours x 52 weeks x $0.10 per kW hour) / 1000 watts per kW x 0.85 efficiency x 12 months a year) = $1.71 per month

Approximate cost savings: $11.14 per month

Powering the Pi and the Dangers of “Backpowering”

The Pi only has two USB ports, so obviously many folks incorporate a powered USB hub to expand its capabilities. At some point, someone discovered that the powered hubs were actually supplying power to the Pi via the uplink between the hub and the Pi. Now you can power your peripherals and the Pi from one outlet. Cool right?

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