I am building a raspberry pi project and I want to use a single power supply to supply 5v 2.5a to the raspberry pi and a powered usb hub in a parallel circuit. From what I've read, in a parallel circuit voltage remains the same, but amperage is split between the different components in the circuit. In theory this should be 50/50 assuming the resistance of the conductors is identical. (am I on track so far?)

I've learned if the conductors aren't the exact same gauge/length/material etc. this will effect how the amperage is divided. My question is if hypothetically I had 5v @ 5a coming from a power supply and I ran one set of leads to microusb power on the pi and one set of leads to the dc jack of the powered hub can I reasonably expect to end up with 5v @ ~2.5a going to each device?

I have already installed a 5.5x2.1 mm female dc jack into the chassis of my project and I really don't have room for an internal power supply, so I am expecting to use an external power supply. I am curious if it is practical to power these two devices from one source.

Also, I have tried to find information on the internet on the effect of resistors on amperage. If I hypothetically used a 5v 10a power supply how would I go about limiting that to 2.5a for each device? If I=V/R then to regulate 5v to 2.5a I would need a 2 ohm resistor? If i connected 5v @ 10a to a 2ohm 50 watt resistor would the current come out of the resistor at 5v 2.5a? Would a resistor change the voltage?

I apologize if these are stupid questions, but I could use some guidance to help me understand these concepts.

Thanks in advance,

 

I've learned if the conductors aren't the exact same gauge/length/material etc. this will effect how the amperage is divided.

no.

Placing 2 wires on a power supply output does not split the current. The current in each wire is determined by the load on the end of the wire. Suppose 5V supplies 2.5 amps to a load. The load must be about 1.99 ohms because the resistance of the wire is in the range of milli-ohms.

What is happening is that you supply a voltage and the load determines how much current flows. The resistance of the wire is supposed to be vanishingly small compared to the real loads.

 

Pardon my ignorance,

So it technically does have an effect, but just a negligible effect that isn't worth mentioning. Is there a way, aside from using two power supplies, to be confident that one load will not be over/under powered? Is it unsafe or unwise to divide the source power between two loads?

 

You're still barking at the wrong tree. Voltage supplies do not force current through loads. They supply voltage and the loads determine the current. Look at your car. Two headlights connected to the same battery with wire. There are a dozen other loads connected to the battery. If it was unsafe to connect two loads to the same power supply, you couldn't even have two light bulbs in your home.

The only time two equal wires matter is when they both go to the same, heavy load. That is the only time when the resistance of the wires is about sharing current equally.

Read this:http://forum.allaboutcircuits.com/threads/ohms-law-for-noobies-or-the-amp-hour-fallacy.69757/

 

Wow that is so much more simple.... Over complicating things is my specialty, glad to see I haven't lost my touch. Thank you!

 

Don't feel lonely, you're the second person tonight chasing an imaginary problem.