Voltage variation

"Jay Honeck" wrote in message
ups.com...
I still haven't had time to work with my A&P to remove my (newly)
flakey JPI EDM-700 unit. (As you may recall, some of the LED segments
that make up the number display are going in and out.)

Someone here suggested that it might be due to low voltage, possibly
indicating an alternator problem. I've started watching the voltage,
and have noticed something odd:

The JPI has its own built-in voltage indicator. It will usually read
13.4 or 13.5 volts. We also have a stand-alone, panel-mounted digital
voltage/amperage meter, mounted a few inches below the JPI. It
usually reads a few tenths of a volt different than the JPI. (I can't
remember if it's up or down...)

a) Is this normal? Why would they read different voltages?

There are numerous reasons, which might be additive:

Gauge calibration.
Different wire paths to the gauges leading to different voltage drop before
the electrons get to the gauge..
Different wire sizes, leading to different voltage drop.
Corrosion in connections.
Loose connections.
Etc.


b) What voltage is normal? Is 13.4 too low?

13.4 is a *little* low, but that could easily be a gauge calibration issue
or a voltage regultor that needs a slight tweak.


Thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"