Electrical Problem

CareBear

CareBear

Filing Flight Plan
Joined
Jun 12, 2008
Messages
11
Location
Birmingham AL
Display Name
Display name:
CareBear
I have a problem that I have not been able to diagnose. When flying, any lights I have on will flicker along with the vacuum gauge, ammeter, and digital clock. With all lights and radios off, the flicker is present (indicated by the flickering ammeter. I pulled the alternator to have it tested and it is okay. All connections have been checked for breaks and looseness. Battery is good and connections are tight. The plane does not have a voltage regulator but it does have an ACU (Alternator Control Unit) that is in the J Box. The voltage varies from 28V down to 24 volts. Has anyone experienced this? Is it possible the ACU has gone bad? Any comments or suggestions are welcome.
 
CareBear said:
Is it possible the ACU has gone bad? Any comments or suggestions are welcome.
Click to expand...
A few question: What are you flying? Make, Model, Year.
* Is this a continuing problem or does it come and go?
* Is it a regular flicker - like might be caused by a blinker of some sort? What frequency? Or is it an irregular flicker?
* Can you get rid of the flicker by powering down radios, autopilot, etc. one at a time?

-Skip
 
I can't see any electrical influence on the vacuum gage unless it is panel lighting. Dirty switch contacts for the alternator field switch can act like a blinker with a regular pulsation from a heating and cooling cycle.
 
Skip Miller said:
A few question: What are you flying? Make, Model, Year.
* Is this a continuing problem or does it come and go?
* Is it a regular flicker - like might be caused by a blinker of some sort? What frequency? Or is it an irregular flicker?
* Can you get rid of the flicker by powering down radios, autopilot, etc. one at a time?

-Skip
Click to expand...

Cessna 172S, 2000 Model. This is a continuous problem. I noticed it about a week ago during my night currency. All lights in the panel flickers. I turned off all non-essentials and the flicker continued. While checking it during the day the same thing happens. Even if I turn everything off it still flickers--I know this because the analog guage needles flicker. I also noticed that when the plane is idling there is no flicker. Any rpm other than idle the flicker is present. I'm at a loss.
 
Graueradler said:
I can't see any electrical influence on the vacuum gage unless it is panel lighting. Dirty switch contacts for the alternator field switch can act like a blinker with a regular pulsation from a heating and cooling cycle.
Click to expand...

Interesting info. I had the alternator tested and it is ok. I also replaced the wiring connector to the alternator.
 
The ACU is in that black box on the firewall. The box is full of connections, any one of which might be loose.

Dan
 
Are things like fuel pumps and radios affected?
Wiggle wires around breakers?
Can you duplicate the problem just running lights off the battery?
How about open the cowl and wiggle all the wire bundles, while the engine is running, just watch the prop.
Voltage changing from 28V to 24V could be alt vs battery.
Maybe loose field wire on alt?
Any maint coincident with start of problem.
Have you got a schematic/wiring diagram or are you working blind?
 
Last edited:
Bad light dimmer? If it were the older rheostat I'd suggest squidging the knob a bit to see if you can get a better contact. I suspect however that this plane has an electronic dimmer for the panel lights and it may be faulty. However a flicker sounds more like a loose connection somewhere.

I know a lot of A&Ps are hopeless when facing electrical problems (don't get me started about the Appalachian-American guys who were poking at my charging system), but it shouldn't be that hard to figure out.
 
Turn the charging system off via the split switch or pull the field breaker, now if the problem is gone you have isolated it into the charging system, if still there....eliminated the charging system.
As someone else said you are looking for either a loose wire/connection or a bad ground, the later most likely associated with the field control.
Tim
 
You must log in or register to reply here.
Back
Top