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I am trying to find a way to split one power supply between a raspberry pi and a water pump. This is pretty much exactly what I want to do. http://arpi.valtio.org/files/2013/10/IMG_0891.jpg

enter image description here enter image description here

Notice how the MicroUsb splits and goes to the buck converter which then goes to the pump. I understand the basics of how this works, I just can't determine what kind of power supply I would need in order to accomplish this.

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    That pictures just shows a big mess. However, if a power supply is supposed to power two loads, it must be rated for the sum of the maximum current each load can draw. – Olin Lathrop Feb 24 '14 at 17:10
  • arpi.valtio.org/files/2013/10/IMG_0893.jpg In this picture you can see the power supply in the left side. It looks like they took the power supply and one of the leads is connected to 2 wires that go to the buck converter and one that stays on as the microUsb. I just don't know what power supply would do that and which wire is which. – RubyNerd Feb 24 '14 at 17:33
  • I found the project here It looks like a simple humidity sensor for the ground humidity. A pipe from the outer shell that contains the water that is connected to the white white pump which exits in the centre part to water the ground. And there is this weird cone shaped thing. I suspect that is a water level detector. There is not much information there and looks really hacky with USB cables and power adapters all over the place. Possibly everything runs of 5v but I cant confirm that. – Piotr Kula Feb 25 '14 at 18:20
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To add on @ppumkin's post The USB cable has four wires, whereas two of those are for power (VCC and GND). The other two are data lines and not connected if the power is coming from a wall wart .

enter image description here

You can connect the PI and the pump to the same power supply if

  • The pump actually runs from +5V
  • The combined current draw from PI+pump is below/equal the maximum current rating of your wall wart

Then you can simply connect two wires to each the +5V and the GND with one 5V/GND pair going to the PI and the other pair going to the pump.

A quick google search showed me that there are indeed small 5V pumps. The start current on the pump was 2A. Combined with the PI the wall wart should provide ~3A.

Do not connect the other end of the micro-USB cable to your computer. Computer USB ports are rated at 500mA max, which would be 6x too low if we assume a 3A current requirement. This could potentially damage your computer.

enter image description here

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If both the pump and Pi use 5volts then simply use those wires to power what you need.

Just as Olin said though, make sure the maximum current (Amps) can be handled by the power adapter. SO the Pi uses about 850ma on full load, and the pump can use, what? 2Amps. Then make sure you have at least a 3A 5volt power supply.

If the voltages are different then you need a voltage regulator, one voltage for each device. At this point it might be better to use separate power adapters or some kind of custom regulated power supply.

I wonder why this got migrated to here.. since its an electronics question... not a Pi related one??

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