I am using a proper voltage and amperage power supply as well. 5V 3A (it is a long cable so needed more amps). Anything less than 3A does not even turn the pi on at all. Please Help!
I currently have a few Raspberry Pi 3's. What is odd is they ONLY power on if the power cord is plugged in to the wall first THEN the pi. If I unplug from the wall and plug it back in, it won't boot up. Thoughts?
I am afraid that "more amps" is meaningless. The Pi will only draw as much current as it needs, and will have problems if the VOLTAGE is too low. See Raspberry Pi Power Limitations for a more detailed discussion.
It is impractical to power the Pi (or any other low voltage device) with such a long lead. There are established electrical engineering techniques to power over extended distances, but ALL involve moving the 5V regulation closer to the load.
If you MUST supply remote power I would suggest a different solution. Use a 5V switch mode regulator e.g. a UBEC to run each Pi, and a 12V (or higher) feed (and don't even think of using CAT5 or 18AWG, even at 12V). The cost of 5V switch mode units, which are readily available, would actually be less than the cost of a suitable cable.
If I was trying to do something similar I would NOT use the µUSB connector, but feed power via the expansion header. This is discussed in the link above.
If you want other options you might consider the EE site. This is really an EE question, which only peripherally involves the Pi.
