[Elecraft] Elecraft Digest, Vol 114, Issue 11

[Don Wilhelm]

Ed and all,

When calculating the voltage drop like this, you need to add the voltage 
drop in the negative side wire as well as the positive side.  The same 
current flows on both sides, so the voltage drop must be calculated 
using the length of both wires.  This fact is often forgotten.  .007 
ohms coming and .007 ohms going.

The other "sneaky" fact of this is that the power supply negative 
terminal and the equipment negative are not at the same potential. That 
can produce noise pickup and amplify RF-IN-THE-Shack problems. Bond all 
equipment together with heavy gauge wire to minimize that effect.

73,
Don W3FPR

On 10/8/2013 7:00 AM, Edward R Cole wrote:
> For my station my Astron 50A PS outputs 14.2 vdc thru about 18-feet of 
> 6awg welding wire to the main station fuse, a 30A BUSS fuse.  Under 
> max load of nearly 30amps the voltage drop is about 0.4v to 13.8v.  
> From my engineering pocket handbook awg6 is rated at 0.3952 
> ohms/1000-feet.  18/1000*0.3952 = .007 ohms.  IR = E:  30*.007 = 0.21 
> volts
>