[TenTec] Herc II Power Source Redux

[Paul Christensen]

> What's a "sense line" ?

The better quality power supplies have an extra set of high-impedance
"sensing" terminals that are used like a digital voltmeter.   On short runs,
they are usually strapped together,

However, on longer wire runs, the sensing terminals are connected to an
extra pair of wires (separate from the supply line) in order to sample the
voltage at the load end.  Since the power supply cables have some voltage
dropped in them as distance and current is increased, the sensing wires
report the voltage of the load back to the power supply.  Any difference
between the power supply output voltage and the sensing voltage is made up
in the power supply...the power supply then increases it's voltage to the
point that it sees the proper voltage at the sensing end.  And, since the
sensing lines are high impedance, they are not subject to voltage drop as
distance is increased.

-Paul, W9AC