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Master solenoid wiring

Rupester

Well Known Member
I noticed today that most of the "standard" wiring diagrams for the master solenoid (aka battery contactor) show the main bus/avionics feed coming off the same terminal as the heavy starter feed. i.e. often the right terminal on the master solenoid wiring diagram. My main bus feed comes off the other terminal, the one sometimes marked "battery" connection. It has been my assumption that both terminals are fully energized when the solenoid is actuated by the master switch.
So, does it make any difference which side of the master solenoid the main bus feed comes from?
 
It absolutely makes a difference. The side marked BAT is the side that connects to the battery. If you connect the main bus to that side it will always be hot.
 
I noticed today that most of the "standard" wiring diagrams for the master solenoid (aka battery contactor) show the main bus/avionics feed coming off the same terminal as the heavy starter feed. i.e. often the right terminal on the master solenoid wiring diagram. My main bus feed comes off the other terminal, the one sometimes marked "battery" connection. It has been my assumption that both terminals are fully energized when the solenoid is actuated by the master switch.
So, does it make any difference which side of the master solenoid the main bus feed comes from?

Whoa whoa whoa! If you dont know how a solenoid works and which side is hot and which is switched hot, dude, stop and do some reading. This is fundamental.
 
It absolutely makes a difference. The side marked BAT is the side that connects to the battery. If you connect the main bus to that side it will always be hot.

Interesting. That makes sense to me, but my system has been operating fine this way for 400 hrs, and none of the devices on the main bus will energize until I turn the master on. In fact, I leave the tail strobe switch on full time to serve as a warning if I leave the master on.
I found the solenoid wiring oddity while troubleshooting a rapidly fluctuating voltage on the E-bus. It fluctuates continuously + or - 0.2 volts. My wiring is scrupulously Nuckoll's Z-11 .... with the exception of my yesterday-discovery that the main bus feed comes off the line side of the solenoid, rather than the load side.
Hmmmmm. I have to ponder this awhile. :rolleyes:
 
Interesting. That makes sense to me, but my system has been operating fine this way for 400 hrs, and none of the devices on the main bus will energize until I turn the master on. In fact, I leave the tail strobe switch on full time to serve as a warning if I leave the master on.
I found the solenoid wiring oddity while troubleshooting a rapidly fluctuating voltage on the E-bus. It fluctuates continuously + or - 0.2 volts. My wiring is scrupulously Nuckoll's Z-11 .... with the exception of my yesterday-discovery that the main bus feed comes off the line side of the solenoid, rather than the load side.
Hmmmmm. I have to ponder this awhile. :rolleyes:

I would track down which Big Cable goes where. You may have another solenoid that disconnects your battery, or possibly the starter solenoid is always hot. I would certainly track this down before making any changes.
 
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