We install tablets on walls that require a constant supply of charging power. We use different cables with various lengths and gauges. Most of our installs use Cat5E so we usually use 2 conductors of that cat5E for the positive and 2 conductors for the negative. I do know that USB chargers all have a voltage of around 5.4 volts and the usual chargers put out between 1 amp and 2.1 amps. We have used 2 amp chargers with charger cables as short as 15 feet and they do not charge.
Q. Is there a formula for determining the proper amperage for a charger output with the variables with the gauge and length? Q. If not, how do I find a charger that will charge my devices with varying lengths and gauge of wire?