Re: Alt Field Circuit Breaker Popping

Rick Hole

With breaker removed, Measure the resistance across the two terminals.  Breaker in= 0 ohms.  Breaker pulled= infinite ohms.

Ideally you would rig a rest with a DC power source, breaker, and load resistor.  Dial up 50 amps.  The breaker should hold.  Dial up higher, perhaps 60 or 70 amps, the breaker should trip within a minute.  

Or test without disconnecting the breaker.  Engine not running, Turn bus on, breaker button pushed IN.  Read battery voltage on both terminals.  Button pulled, battery voltage only one terminal, 0 volts on the other


Rick Hole


From: Q-LIST@... [mailto:Q-LIST@...]
Sent: Monday, July 29, 2019 11:30 AM
To: Q-LIST@...
Subject: Re: [Q-LIST] Re: Alt Field Circuit Breaker Popping



Update:  I’ve located a 50amp breaker labeled MAIN.  I turned on Master, electronics come on, and then I pulled the 50amp breaker.  Nothing turned off.  I’ve removed the breaker and would like to know how to test to confirm if it’s working or not.  


Should all electronics turn off if I pulled the MAIN breaker?


On Jul 29, 2019, at 11:59 AM, Rick Hole r.hole@... [Q-LIST] <Q-LIST@...> wrote:


An open alternator output, for example 50a breaker tripped or disconnected wire could cause the field breaker to blow only if the regulator suppling full voltage to the field draws enough current to trip the 5a field breaker. This should not be possible but if the 5a breaker is old and tired and, say, tripping at 3a your could see it trip. I have never seen this happen though. 

Don’t overlook wire fault as a cause, insulation worn through and he wire touching something grounded etc. 

Rick Hole

Email: r.hole@...

On Jul 29, 2019, at 10:23 AM, q2pilot@... [Q-LIST] <Q-LIST@...> wrote:


Ok, great news.


Now disconnect the Field wire from the back of the alternator and leave hanging.

Does the 5A break still blow?  If it does it's a bad regulator.  If it doesn't blow now, then we may have a shorted field in the alternator.


: )



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