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I want to place my Raspberry Pi in a remote location to act as a surveillance camera and need to run a power-ONLY USB cable over a long distance of 30 to 50 feet.

Can I safely extend a normal USB 2.0 cable by just connecting the VBUS +5V RED and black GND wires to one pair of a CAT-5 cable reusing the TYPE-A and Micro-B connectors from the USB cable?

I would leave the data wires disconnected.

Piotr Kula
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HeatfanJohn
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4 Answers4

9

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.

Milliways
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4

If you are planning to have Cat5e running to it then why not just use PoE.

PoE injector/splitter kits are relatively cheap, here is one which would likely work for your situation as supports 5V output.

3

it may introduce a whole lot of inductive noise and depending on your environment it may work or your board may keep resetting or getting all kinds of glitches. (such a cable acts as a huge antenna and there will be bad spikes in power both ways - and RPi doesn't have big capacitors to compensate for that).

Just run a mains AC extension cord and put a USB charger at the destination to power RPi up.

SF.
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3

As milliways has answered you will get a steep voltage drop on such a distance using 5volts.

This is common problem in all long distance power transmission.

The best solution is to use a 24 Volt power supply and use a 5 volt regulator on the Pi side. There are cheap modules available or you can easily make your own regulator using a capacitor and a voltage regulator 78xx. (Sparkufun) (Wikipedia)

But it would be more efficient to use a switching regulator V78-1000 if you want to save power.

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The reason using 24 volts is better is:

  1. The obvious voltage drop problem on a long wire.. this wont matter if you regulate down to 5v
  2. Higher volts does not need higher amps (its actually opposite). So you can use a 0.5amp power supply but when regulating you will inface get more amps to use on the 5v side! This will help use a thinner copper wire (like network cable) which will reduce the voltage drop (less resistance)

FYI - Some POE standards uses up to 50 volts to power remote devices.

Just a side note to consider but not critical - As commented by SF. It is better to send AC current- but 220volt might be dangerous so a compromise is sending 24volt AC and rectifying (also easy and cheap using 4 diodes) and regulating it at the Pi. That is because of various inductance problems and stuff I am not really all that familiar with.

Piotr Kula
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