I've been experiencing momentary loss of power to my autopilot (Dynon A/P 74) and EMS (D-100) when keying the mic on my primary radio (Garmin 430W). The voltage reading on the EMS is 10.8 inflight give or take a point or two. I'm assuming this is the Essential (avionics) bus I am viewing. I'm attaching a link to the electrical schematic for my AC and a photo of my EMS inflight readings.
I finally decided to take the plane to an avionics shop and here are the findings of the technician. I'd really appreciate second opinions on his conclusions.
The voltage you saw on the Dynon was indeed correct. You had 12.5 volts on the main bus but only 10.5 on the avionics (essential) bus when I first checked things. You are dropping an additional 0.5 volts when you key the radio, so the voltage got down to around 10- ish volts which is when the displays blanked during transmit.
AS PER THE TECH:
There is some kind of rectifier/diode in line with the essential bus feed wire that is dropping 1 to 1.5 volts and I have no idea what it is for. That, I believe, is most of your problem.
Additionally, after I wiggled the terminals on the avionics master switch, that mysterious rectifier, and the essential bus bar to check the security and attachment of the wires, I noticed the voltage came up to 11 - 11.5 volts, which brings up another issue I think will continue to plague you. That is the use of push-on terminals on high current carrying circuits.
I highly recommend changing those to ring terminals with screws. If the switch does not have screws then I would install a switch that does. Push-on terminals are notorious for intermittent connections with high current loads (more than 5 amps or so I’d say) – they get hot, begin to build up resistance and drop voltage which makes them get even hotter and compound the problem, eventually failing. The problem is even worse in high humidity climates like ours because corrosion builds on those terminals over time and compounds the problem we’re discussing.
In a 14 volt system, it is essential that you carefully manage any voltage drops, be it from using too-small gauge wires or from poor terminations (bad crimps, poor quality terminals, loose screws on breakers/switches, etc). 28 volt systems give you room to breathe, but 14 does not. Things begin to do strange things below 11 volts so that only leaves you with 3 volts of loss to work with as opposed to 12-13 volts of loss to manage on a 28 volt system. Simply put, 28 volt system is more forgiving than a 14 volt system…..
Hope this helps. Remove or replace that rectifier/diode behind the panel and change the push-on terminals to ring terminals and I think your problems should be solved.
Thanks for comments
I finally decided to take the plane to an avionics shop and here are the findings of the technician. I'd really appreciate second opinions on his conclusions.
The voltage you saw on the Dynon was indeed correct. You had 12.5 volts on the main bus but only 10.5 on the avionics (essential) bus when I first checked things. You are dropping an additional 0.5 volts when you key the radio, so the voltage got down to around 10- ish volts which is when the displays blanked during transmit.
AS PER THE TECH:
There is some kind of rectifier/diode in line with the essential bus feed wire that is dropping 1 to 1.5 volts and I have no idea what it is for. That, I believe, is most of your problem.
Additionally, after I wiggled the terminals on the avionics master switch, that mysterious rectifier, and the essential bus bar to check the security and attachment of the wires, I noticed the voltage came up to 11 - 11.5 volts, which brings up another issue I think will continue to plague you. That is the use of push-on terminals on high current carrying circuits.
I highly recommend changing those to ring terminals with screws. If the switch does not have screws then I would install a switch that does. Push-on terminals are notorious for intermittent connections with high current loads (more than 5 amps or so I’d say) – they get hot, begin to build up resistance and drop voltage which makes them get even hotter and compound the problem, eventually failing. The problem is even worse in high humidity climates like ours because corrosion builds on those terminals over time and compounds the problem we’re discussing.
In a 14 volt system, it is essential that you carefully manage any voltage drops, be it from using too-small gauge wires or from poor terminations (bad crimps, poor quality terminals, loose screws on breakers/switches, etc). 28 volt systems give you room to breathe, but 14 does not. Things begin to do strange things below 11 volts so that only leaves you with 3 volts of loss to work with as opposed to 12-13 volts of loss to manage on a 28 volt system. Simply put, 28 volt system is more forgiving than a 14 volt system…..
Hope this helps. Remove or replace that rectifier/diode behind the panel and change the push-on terminals to ring terminals and I think your problems should be solved.
Thanks for comments
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