Alternator (Ammeter) Problem (Piper)

On 2018-10-29, wrote:

I'm working on a Piper Cherokee that's ammeter is showing a mild draw
and then a drop. It maintains a measurement of 10amps for maybe 10seconds
then it drops back off to zero. The pilot removed the alternator took it
to get tested then brought it back. The pilot also had the voltage regulator
changed out. Anyone had a similar problem? I can answer more questions this
was just a brief description.

Speaking as a Cessna driver, I see this routinely (although my meter kicks
up to 20 or 30 amps when I first fire up). The alternator is replenishing
the charge that was drawn from the battery by the starter; the meter settles
back down to zero after a minute or so when the battery is topped up.

However, in a Cessna the ammeter measures how much juice is going into
or out of the battery (it goes positive or negative), whereas in a
Cherokee the meter indicates how much the alternator is putting out,
regardless of what's happening to the battery. It can never give a
negative indication. Upon starting, the meter would show the charge
the alternator is putting back into the battery, in addition to whatever
other electrical loads are on the bus. After the battery is topped up,
the meter should drop to what was required to supply whatever electrical
devices are turned on. If you haven't yet turned on lights, radios,
etc. this would be close to zero. (Sorry, I forgot to closely watch
the ammeter on startup last time I flew a Cherokee.)

Have you tried putting a load on the system? Once the engine is running
and the meter has dropped to zero, try turning on the landing light.
You should see a good indication on the meter then. If not, there's
a problem somewhere. Make sure the landing light isn't burned out,
though. :-) (I recently detected a burned-out landing light in broad
daylight by this lack of response on the meter.)

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