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I wonder whether it is Ok to power a raspberry pi using a ribbon cable.

Reading this information, I think it is not possible because 1.8A is recommended.

Is it like that? I have a really limited knowledge about electronic stuff.

I will only connect the device to a network using Ethernet. I would also like to read a i2c pin and a gpio. that's all.

The length of the cable is like 10 cm. I don't understand the "strand" stuff.

In his answer, CharlieHorse says that 1.4A is the maximum, but in the table I provide it says that for power transmission a cable of 28 AWG can only handle 0.226A. Am I missing something?

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    Of course it depends on what is connected to your Pi. Mine are headless and I doubt they ever use more than 500 mA. – joan Feb 2 '16 at 15:03
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    Hello and welcome. There are two very important facts missing: the length of the cable and whether it is possible to use multiple strands for powering. – Ghanima Feb 2 '16 at 15:21
  • I think its fine to try but beware the 5V pin bypasses regulation and fuses. – goldilocks Feb 2 '16 at 15:29
  • related to the add-on question: electronics.stackexchange.com/questions/33522/… and also the site you've linked yourself pointing out which is what. (makes me think it's ok, since only a few strands are used for powering) – Ghanima Feb 2 '16 at 15:49
  • Some cables/wires use a single, solid core (which tends to be stiff and is great for use with breadboard type prototyping) most others are made up of many smaller "strands" run side-by-side (which is much more flexible, i.e. can be bent and moved around without breaking) in that the conduct is specified as two numbers the diameter of each strand and (always an integer) the number of strands in a core. A core is one "way" or discrete conductor in a cable or lead - e.g. a GPIO interconnection on the first generation RPis is likely to be a ribbon cable with 26 cores. – SlySven Feb 2 '16 at 19:03
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The maximum load on a 28 AWG wire is 1.4 amps. This is a max, so it's not recommended to even get to this point. Your best bet would be to power your Pi with a 2 amp cell phone power supply.

  • Charlie, do you have a clue on the max amperage wrt the linked table (Maximum amps for power transmission vs. chassis)? – Ghanima Feb 2 '16 at 15:38
  • Yep. The max for power transmission over a 28 AWG cable is .226 amps. This is what the OP is trying to do. – CharlieHorse Feb 2 '16 at 15:52
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    ... but that's not what you wrote in your answer. – Ghanima Feb 2 '16 at 15:53
  • I looked at the chassis entry. Still, I wouldn't try to get 1.8 amps through such a small cable, particularly one designed for data. – CharlieHorse Feb 2 '16 at 15:54
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    This is rubbish. There is no maximum current for any size of cable. It depends on length, temperature and allowable voltage drop. The Wiring Rules for domestic installations have a range of currents depending on enclosure. – Milliways Feb 3 '16 at 0:40
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Besides the already mentioned max. amperage of 1.4 A (Maximum amps for chassis wiring) / 0.23 A (Maximum amps for power transmission) (see here for further insight) there is another issue to consider - voltage drop along the wire:

Assuming 1 A drawn by the Pi and additional peripherals (note this could be different depending on the peripherals and load case of the Pi). Consider the power supply provides 5.25 V (acceptable max. voltage, make sure as the charger/power supply might not hit that limit) and at the far end a voltage of 4.75 V is required (acceptable min. voltage = input voltage of the Pi). So a total voltage drop of 0.5 V is allowed. So with

U / I = R = 0.5 V / 1 A = 0.5 Ohm

the max. acceptable resistance of the wiring is 0.5 Ohm. AWG28 has a resistance of 0.21 Ohm/m. So, assuming 1 m distance between load (the Pi) and the power supply - equals 2 m of wiring (back and forth) - the total resistance is already bordering acceptable limits.

So it really depends on the length of the ribbon cable wiring. If it is possible to use multiple strands for powering (both VCC and GND!) a wider margin of safety will be achieved.

Update to reflect question's edit:

With a length of 10 cm the total resistance will be 0.04 Ohm and at 1 A a voltage drop of 0.04 V which would seem perfectly acceptable.

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The answer is yes.

I just checked my original Pi.

That was powered through a floppy disk ribbon cable which is apparently 28 AWG.

I used one end of the cable plugged in to the 26 pin expansion header. The other (female) end I used by plugging in jumper wires to connect to a breadboard. The breadboard was powered by a 5V UBEC. So the power went from the UBEC to the breadboard to the Pi via the 28 AWG ribbon cable.

You might be able to see the cable + wires in https://www.youtube.com/watch?v=rrRg1guojQE

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