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Troubleshooting odd issues

jeffsvan

Well Known Member
Trying to help my hangar neighbor diagnose some odd issues in his plane.
I'm going there tomorrow with my voltmeter.

he has a split bus bar with one side showing 12.3 volts and the other showing 14.1 while the engine is running.

He shows a voltage drop of .5 volts on the 12.3 side when the push to talk switch is depressed.

also has some alternator whine when transmitting on the #1 radio.
when receiving both radios are quiet.


anyone have any thoughts??

I'm going to check for proper grounds, & the headset jacks for isolation washers.
Going to check the alternator for ripple voltage/bad diode.
Will check the voltage regulator too. Seems to me both electrical busses should be regulated the same. How they differ by 1.8 volts is odd.
 
The first step is to look at what is providing current to the second (12.3V) bus bar. There is a resistance in that path somewhere. Loose crimp, bad breaker, something.
 
The low voltage buss is feeding the radio, that causes an even further drop when it is keyed on? You have a poor connection between the alternator and that buss. With electrical power on (engine off) and radios, etc., on, do you see that buss lower than the other? If so, use your voltmeter and trace back the wire that feeds that buss, thru switches, relays, etc, until you find where that voltage is lost. Replace or repair the high(er) resistance switch, connection, etc.
I think the alternator noise is a red herring here. I’ll bet the intercom or audio panel is on the same buss, and when you key the transmitter it draws more current, and the buss voltage drops so low that a small voltage regulating/filtering chip in the intercom can no longer function, and you hear the whine.
 
Does he have a diode between the two busses? They can cause a voltage drop.
 
Got contactors in the individual feeds? Try loading each side separately, and independently and watch the voltages. If it drops a little as load goes up, the contactors (drop across them) is probably the first thing I’d check based on knowing zero about the architecture.
 
I checked the electrical and charging system and feel the alternator and battery are OK. There is a Zeftronics voltage regulator on board. All three items are recently installed in the last few years. The alternator seems to provide clean power. My tester showed very little ripple. I do not feel these are causing the alternator whine.

I checked the headset jacks and made sure they had the proper isolation washers. everything is ok there.

First thing I noticed and did not like.
There is one 16 inch length ground wire attached to the frame that reinforces the foot well.

It is aprox. 18 or 20 gauge and has a eyelet on each end.

There are 4 ground wires coming from the radio stack. Each with an eyelet crimped onto the ends. The radio stack wires are connected to the single ground wire in a bundle with a brass screw and locknut sandwiching them together.

I need to reference my radio manuals, but i recall them calling out thicker gauge wires for BOTH power and ground.

Having 4 ground wires choke down to 1 wire is not proper.
 
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