[Elecraft] K3 Suddenly died

[Mark Bayern]

> If a conductor (wire) is rated for 20 amps at 120 volts for a given length
> (due to it's R),


1 -- The voltage rating of a conductor has to do with its insulation.
It has nothing to do with the potential current flow or what you're
calling the wire's "R".

2 -- The applied voltage has no effect on the voltage drop of a
conductor. Look at Ohm's Law again. The voltage drop is due to the
resistance of the conductor (wire) and the current flowing through
that conductor. A conductor with a 2 ohm resistance will have 2 volt
drop when 1 amp flows. That 2 volts is the same for any applied
voltage as long as there is 1 amp flowing. It can be a 12 volt system,
a 120volt system or a 1200 volt system. One amp flowing through a
conductor that has a 2 ohm resistance will have a 2 volt drop.

> ... and we want to use that same wire for 20 amps at 13.8 volts,
> we must reduce R by either increasing the wire size, decreasing the length,
> or a combination of both.

Wrong. If the conductor is good for 20amps it is good for 20amps
_at_any_voltage_. This is probably what activated Jim's "Nonsense
Alert!" beacon.

So ... why use larger conductors at lower voltages? Because for most
uses we want to transfer power. To keep the power the same, we need
more current at lower voltages. Example: A cable that supplies 120
watts at 120Volts needs to conduct 1 amp of current flow. (Power =
current times voltage. P = I * E ). To get the same 120watts from a
12V system you will need 10 amps of current flow. If we tried to use
the same cable at 10 times the current we would have 10 times the
voltage drop. To avoid that we use a larger diameter conductor.

Mark  AD5SS