To those who replied on, and off line, I don't mind factual disagreement,
but aren't we above insults? It doesn't get much simpler than this.
R is the resistance of the conductor (wire).
I is the current flow.
E is the Electromotive Force, or voltage.
Ohms law is E=IR, and with simple algebra is I=E/R
If a conductor (wire) is rated for 20 amps at 120 volts for a given length
(due to it's R),
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.
Dick, n0ce
-----Original Message-----
From: Jim Brown
Sent: Monday, October 07, 2013 1:04 AM
To: [email protected]
Subject: Re: [Elecraft] K3 Suddenly died
Nonsense alert!
73, Jim K9YC
On 10/6/2013 10:22 PM, Richard Fjeld wrote:
When we think of wire gauge requirements for amperage needs, we need to
remember the amperage rating for wire is given for house voltage,
typically
~117 volts AC (in the US). For lower voltage at 13.8 VDC, we need larger
wire
size (smaller gauge number). What often saves us is short lead lengths.
Still, if one measures the voltage drop of a conductor under load by using
a DMM with a test lead at each end of the wire, a drop will be seen if the
wire size is not adequate for the load. (Emphasis on 'under load'.)
The voltage drop across a resistance (in this case a conductor) is
directly
proportional to the amount of current flow through the resistance. At
idle
current, very little voltage drop will be measured in the resistance of
the
conductor.
The 12V jack on the back of the radio cannot be used to accurately measure
voltage drop in the power cable, but the voltage measured during key-down
will be approximately 1.4 volts less than the PS voltage if the cable is
good.
An RCA plug can be wired to make the test connections safely.
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