Rod,
A Fluke 87 DVM will also give you peak and low readings.
Paul

"Rod McInnis" wrote in message
...

"Jack Goff" wrote in message
m...
Well... I went out this afternoon and this is what I found.

A DVM on the battery posts measures about 13.8v when it's running.

Okay, the battery is not being damaged.


All the while the boat voltmeter reads pretty much pegged full scale...
18v.
The voltmeter has obviously gone south. That should be a lot cheaper
than
a
voltage regulator. :-)


Use the DVM to measure the same point that the voltmeter is seeing.

Even if they don't agree, it is possible that the voltmeter is not "bad",
it
just might be making different assumptions.

When you take a measurement of a "DC" signal, you basically have to assume
that the voltage is constant. If the voltage is not constant, how the
meter
deals with it can give you wildly different readings.

Usually, an "analog" voltmeter will give you a nice average of the signal,
as the mass of the meter movement dampens things out. It is possible that
even an analog movement has some non-linear components in it that might be
causing it to detect peaks.

Cheap digital meters can give very erratic readings as they get sampling
errors. Better digital meters will filter out the higher frequency noise
so
that it can get reasonable measurements.

It is possible that the voltage output from your outboard has become very
"spikey", and that the in dash voltmeter is responding to the spikes
instead
of the average.

Rod