jma201 Posted September 10, 2019 Report Share Posted September 10, 2019 I noticed something concerning on my last flight. When starting the engine with the avionics master off, the audio panel and number two radio briefly lit up with power. After engine start, I turned on the avionics master and everything came on as normal. Any thoughts about what might be happening. What would cause the avionics buss to get power with the avionics master off? Thanks! Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted September 10, 2019 Report Share Posted September 10, 2019 That's normal. The avionics relay is designed to fail ON, so when you turn the master switch on, the avionics solenoid takes a moment flip from the ON to the OFF position, so you might see your radios or LEDs flash for a moment. When you turn the avionics relay ON, it actually cuts power to the avionics solenoid, allowing it to return to the ON position. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted September 11, 2019 Report Share Posted September 11, 2019 Yes and no... The idea behind the avionics relay is to not be sending waves of current to the avionics... The avionics relay is wired to be on in the event the relay fails... What you are describing is an Avionics relay that isn’t working properly... it isn’t switching fast enough to avoid sending power To the avionics... then when it does switch the avionics go off... Probably time to get a new avionics relay...faster and cheaper than trying to OH the existing relay... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
PT20J Posted September 11, 2019 Report Share Posted September 11, 2019 If I understand correctly, the radios came on while you were cranking. If the battery were weak and/or the starter drawing too much current, the bus voltage might drop enough during cranking to cause the the avionics bus relay to drop out and power up the avionics bus. As described, the fail safe design is that the relay must be energized to depower the avionics bus. Skip Quote Link to comment Share on other sites More sharing options...
jma201 Posted September 11, 2019 Author Report Share Posted September 11, 2019 Thank you all for the replies. One more thing for the upcoming annual punch list. Quote Link to comment Share on other sites More sharing options...
larryb Posted September 11, 2019 Report Share Posted September 11, 2019 I agree with the weak battery theory. Quote Link to comment Share on other sites More sharing options...
EricJ Posted September 11, 2019 Report Share Posted September 11, 2019 I had this, where turning the key to START turned all the avionics on. The avionics relay had been "fixed" by a previous AI that mistakenly thought it was wired wrong. IIRC there was a relay involved that had both Normally Open and Normally Closed sides and the fix was mostly just swapping sides on that relay. Quote Link to comment Share on other sites More sharing options...
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