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Master Solenoid issue?

Rupester

Well Known Member
My mysterious varying low voltage problem has returned. Argggghhh.

Today I began by checking voltage at several points:
At EFIS#1 per the GRT display, master on - 11.4V (Hmmmm.)
Across the battery - 12.8V (charging must be OK, despite recurring alarms!)
At the E-bus switch - 12.6V
At the E-bus feed, switch on - 12.6V
At the main bus feed, master on - 11.4 to 11.5V.
When I brought up the EFIS displays via the Ebus, there was ~2 amps drawing on the battery and a voltage of around 12.5. When I then switched the master on, the amp draw went to -9, and voltage dropped to 11.4. (The tail strobe does come on with the master, but is not more then 2 amps max)
Is it possible I have a master solenoid that's drawing inordinate current, thus explaining the low voltage alarms, even though the battery is 12.8 volts after landing?
 
every relay switch or contactor pair have voltage drop if contacts are bad!
or they are not rated for current they pass.
diodes,too small wire gauge also can play role. at higher amps.

start with wiring diagram of your AP. Use battery charger or other constant power device dont drain battery.
load serquit you testing to 50% of the max Amps (automotive sialedbeam good load) and start checking voltage drop at each side of contact pairs
from battery to the load.
 
What's the "normal" voltage drop across the master solenoid? ( In general, I would assume close to zero.)
.... how about it's current consumption?
 
from what I work with, low current, .1 VDC drop per connection .5 max. Battery connections, .2 VDC drop per connection 1.0 max. so a connection is cable to cable end, contactor, ect. I do these tests under the circuit design load switched on.
 
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