Dan,
No voltage across the contact is unrealistic. O.5 volt is considered to
be the acceptable limit.
If you replace the master and starter solenoids. Have your A&P install
diodes reverse to the flow across the contractor terminals. The will
prevent the contact from arcing when they disengage. It is the contact
arcing that increases the resistance and causes the voltage drop. 0.5
volts across the contacts is 0.0013 ohms.
Michelle

Dan Thomas wrote:

Often overlooked are the master and starter solenoids. These things
get burned contacts and they begin to present a resistance that shows
up as reluctant cranking. A voltmeter placed across the solenoids' big
terminals should show 13 volts when the system is off, and NO voltage
when it's on (or cranking). Any voltage while the solenoid is closed
indicates resistance across the contacts. Even a small amount of
resistance at high current flows will cause significant voltage drop
(E=I*R; A .02 ohm resistance at 200 amps gives a 4-volt drop). Check
the cable connections the same way. Check both the master and starter
solenoids with the engine cranking.
An ohmmeter isn't really good enough to detect bad solenoid
contacts. The resistances are small, and increase with heat caused by
electical flow. An ohmmeter won't detect the heated resistance.


Dan



--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity