Voltage Readings

[John Suter]

Hi Scott,

--- Scott Forman <sforman@...> wrote:

> I don't know a lot about electricity, so I need some
> help here:

Let's first chat a moment about 12V batteries. To
charge at all, they must be presented with 14.1 volts
or more, and a fully charged, good, 12v battery, "at
rest" (i.e. without a load, and roughly an hour or
more after charging has ceased) should indicate 12.65v
while a "discharged" battery under the same
circumstances will show 12v or less. Note that if the
battery is not "at rest," measuring its voltage will
not present an accurate picture, and it really needs
to be checked with a "Load testing" device for true
accuracy.

It is common to hear an inverter/charger "float
charges" at 13.4 or 13.1 or so; however, "float
charging" is generally understood not to mean "adding
any charge," but to be an "in-between state" where the
charger system has determined charging (14v+) is no
longer needed, but monitoring is necessary in the
event charging becomes necessary.

> What should the voltage reading on the engine volt
> gauge be while
> driving?

Engine alternator charging is controlled by a
regulator system which adjusts both voltage (still
must be above 14v to charge) and amperage, which is
"current flow." The two readings are positively
correlated, though not necessarily, directly, in a one
to one relationship.

Voltage and Amperage can be read from the dash
gauges; however, the gauges are generally reading
totals and not simply the portion which is "battery
charging." Therefore, depending upon the regulator
settings and total system demands for current/power,
the regulator may provide voltages from 12 through 18,
and amperages from virtually nil to the maximum output
of the alternator. For most Birds, we'd not find it
unusual to see around 14 1\2 volts and 20-30 amps.
Significantly higher or lower of either, would be
cause to ask "why," but not necessarily become
alarmed.

> I have always thought that when driving
> normally, the volt
> gauge should read somewhere around 14.5 when the
> alternator is
> putting out properly. Last night, when driving home
> from a repair
> shop where several items were replaced (including 4
> new batteries),
> the gauge was only reading a bit above 12 when
> driving. Should I be
> concerned about my alternator?

With the engine running, turn on all headlights
and 12V circuits and see what you find, especially the
amperage.
No change, and assuming the gauges are reasonably
correct, I might be questioning the regulator. If it
is found normal, then the alternator.


> Also...what is the purpose of the 'Amps' gauges?
> What do they
> demonstrate? My 82 FC has one on the dash and also
> one at the power
> switch in the step well.

Generally, the one(s) at the step well are measuring
the amperage of the 110V circuit(s). When connected
to shore power, turn on an air conditioner compressor
and watch the amperage gauge.


> Neither gauge ever seems
> to move much if at
> all. What should these two gauges be showing me?

Hopefully, some of the above may have answered this
for you, Scott.

>
> Thanks
> Scott Forman
> 82 FC35RB
> Memphis

John Suter





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