BeechTalk - BT

Username Protected · **Posted:** 06 May 2021, 22:01

So, tonight Michelle and I loaded up the dogs and our bags in the 182 and departed for Lake Havasu. Shortly after leaving the pattern I heard a slight pop in my headset and looked down and the STEC 30 autopilot was locked up and I thought that was odd. I turned it off and rebooted it and it rebooted fine. Then I looked up and noticed that the alternator charging gauge was on zero. I looked down and saw that the 60 amp alternator breaker was kicked so I started a return to the airport to land. (Homie don't reset breakers in the air...

) After we landed I tried to reset the breaker and it kicked back out right away. I shut off the avionics master switch as well as the autopilot and tried to reset the alternator breaker and no joy. I shut off the master switch and reset the alternator breaker but it tripped again when I switched on the master switch. If I'm thinking right I may have a short on the buss or shorted winding's in the alternator? :scratch:

Anyway, we're back on the ground at home enjoying a margarita and will tackle it in the morning with my mechanic. My slogan has always been that I don't need to be some where that bad. :rofl:

Dave

Username Protected · **Posted:** 06 May 2021, 22:20

Shorted alternator or a short on the big cable between the alternator and the buss.

Username Protected · **Posted:** 07 May 2021, 07:34

Wherever the short is, it has to be downstream of the circuit breaker.

Username Protected · **Posted:** 07 May 2021, 07:44

Good decision making!

:thumbup:

Username Protected · **Posted:** 07 May 2021, 08:36

What Paul said....my money is on a shorted cable.

Username Protected · **Posted:** 07 May 2021, 08:57

Username Protected wrote:

What Paul said....my money is on a shorted cable.

Or possibly an internal short in the master switch? :shrug:

Dave

Username Protected · **Posted:** 07 May 2021, 09:35

Check connections on back off the Alt. Maybe a loose or grounding output wire..

Username Protected · **Posted:** 07 May 2021, 09:36

Username Protected wrote:

What Paul said....my money is on a shorted cable.

Or possibly an internal short in the master switch? :shrug:

Dave

Username Protected · **Posted:** 07 May 2021, 10:21

Username Protected wrote:

the 60A breaker is just for the large lead and the alternator itself.

That schematic was helpful. So if the 60A breaker is blowing, the fault must be downstream of that, which eliminates anything on the alternator itself, or the large wire to the breaker. Just sayin'...

Username Protected · **Posted:** 07 May 2021, 10:37

Username Protected wrote:

the 60A breaker is just for the large lead and the alternator itself.

That schematic was helpful. So if the 60A breaker is blowing, the fault must be downstream of that, which eliminates anything on the alternator itself, or the large wire to the breaker. Just sayin'...

Username Protected · **Posted:** 07 May 2021, 11:11

Look first at places where wires are adjacent to grounded metal parts - repetitive vibration wearing a hole through the insulation of the wire. Note, also, that it need not be a "big" wire to trip that breaker, but rather, any wire connected to the hot side.

Special places to look are anyplace a wire comes through a bulkhead (like the firewall) - grommets wear out over time, and the sheet metal becomes a vibrating knife.

One other "dark horse" candidate would be a screw or other metallic bit of detritus falling down and bridging between the bus and the panel / structure.

Username Protected · **Posted:** 07 May 2021, 11:59

Username Protected wrote:

The question is, which way is downstream?

You make a good point. A circuit breaker is bi-directional so I guess it's possible for the ALT breaker to trip if the battery were connected to the buss and there was a short between the circuit breaker and the alternator. In theory, the diodes in the alternator would isolate the internals of the alternator. Does a C-182 have a split master switch so the battery can be connected to the buss but not the alternator? That might be a good troubleshooting step.

Username Protected · **Posted:** 07 May 2021, 12:24

Just like the diagram shows, the output of the alternator is always connected to the buss. You can take the master switch out and throw it in the trash and the alternator will still be connected to the buss. When the OP turns on the master switch, battery power is applied to the buss, through the circuit breaker and out the big wire to the alternator. With the engine not running, the alternator isn’t outputting any power TO the buss.

Username Protected · **Posted:** 07 May 2021, 13:34

Well Dave, you can always do what I used to do as an electronic tech back in the day. When we'd get a circuit board with a dead short on the power buss that we couldn't find, we had a desperation move. We'd hook a car battery across the buss and whatever the problem was - usually a solder whisker - just went away in a puff of smoke. Sometimes, though, the results were spectacular :rofl:

Username Protected · **Posted:** 07 May 2021, 13:42

Username Protected wrote:

Well Dave, you can always do what I used to do as an electronic tech back in the day. When we'd get a circuit board with a dead short on the power buss that we couldn't find, we had a desperation move. We'd hook a car battery across the buss and whatever the problem was - usually a solder whisker - just went away in a puff of smoke. Sometimes, though, the results were spectacular :rofl:

I've actually done that many years ago! Was usually a big pcb with lots of TTL. One of them is shorted, but which one? Put 5V on it from a power supply and the bad one explodes.

Nowadays we just see which one is getting warmer than the others, no need to risk melting tracks.

Electrical Problem Cessna 182