A Tale of Two Power Supplies - why good is good and better is best
The purpose of this post is to discuss two power supplies, and their ratings, why they are good, and why one is better.


The pic above shows two power supplies available on the market which may be used with the PineA64 (or the Raspberry PI, for that matter).  Both of these supplies are international supplies , which means they have interchangeable heads which match the mains of several different prominent world locations; these have been set to mains U.S. 120v AC.   The black PSU on the right is good, the white PSU on the left is better;  why?

The reason comes down to the AC rating (the size of the mains primary winding) the length of the cord, the gauge of the wiring in the cord, and the rating of the DC output volts & amps. The rating of the PSU is on the label ; the following pics show the labels of the two supplies high-lighting the positive attributes of each supply.


The black supply in the pic above is (good) has 22 AWG two conductor cable of reasonable length (about 1 meter) and is rated at the mains for .35 amps and provides an output of 5v @ 2.0A or 2000 ma. The higher the gauge number, the smaller the core diameter of each conductor and the less current it can carry effectively without adverse voltage drop. 22 AWG is good, but is not the best.  A range of 18-20 AWG is satisfactory, and 22 AWG is on the low side.  This power supply is only rated for .35 A on the mains side, and can only deliver 2000ma on the DC side at 5v. This also is 'good' for the PineA64 (or Raspberry PI 3) but is not the best.  


The pic above shows the Raspberry PI international PSU.  It has 18 AWG two conductor cable and is rated at the mains for .5A.  The DC rating of this supply is 5v @ 2.5A or 2500ma.  This supply is the best supply for the PineA64 (or the Raspberry PI 3) because even though its power cord is about 15cm longer, its core diameter two conductor cable is superior;  also the mains primary is beefier (.5 A) and its DC output is 500ma higher for the same voltage output of 5v.   

It is preferable to shorten the power cord of this supply (if possible) to further reduce the voltage drop which occurs with DC voltages transmitted over a distance (the shorter the cord, the better the stability of the switching supply). 

The white supply listed above is specifically listed as a 'switching' adapter; while the black supply shown above is not. This does not mean 'for sure' that it is NOT a switching supply, only that it is not rated as a 'switching' supply and may in fact be a linear supply.  A 'switching' adapter is more efficient than a linear supply, and better able to maintain a steady 5v at full rated current loads - 2500ma in this case.

This is in no way intended to be disparaging; it is intended to show what is available and high-light the differences.
marcushh777    Cool

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A Tale of Two Power Supplies - why good is good and better is best - by MarkHaysHarris777 - 08-09-2016, 10:38 PM

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