C172 Generator braked tripping


Filing Flight Plan
Jul 9, 2023
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today went for a night flight. i have a voltmeter installed in the cig lighter socket.
while doing runup, the generator light goes off as usuall but the volotmeter not showing charge (stable at 12.5v). I noticed that the generator braker was poped. Pushed it back in. Re did my runup, the red lignt still goes off and voltmeter still stable.
i went fir my 1h flight+1h patern exercice, the voltmeter veries between 11.8 and 12.9v, never over 12.9v, wich i assume means it s not charging.

what Could be the reason?

p.s : i changed the battery last week and polarized the generator on the regulator, the volmeter showed up to 13.9v during the flight.
At night, it’s likely you are using what the generator is putting out, but probably not putting out as much as it should. If it gets to 13.9 ever, then it’s working, but maybe not putting out as much as it should. If it wasn’t charging, then the voltage would continue to decrease. If it read 11.8 at any point, it would never go up unless maybe if you turned everything off, if the generator wasn’t charging at all.
what Could be the reason?
Probably for the same reasons from your last charging problem thread. The fact you flew a 2 hour night flight with a known battery charging problem speaks more to the underlying reasons why your aircraft is not working properly than anything. Not much I can help you with on that except to recommend have a mechanic actually check/fix your aircraft and dont fly it until he does.
As Paul Simon once sang, "I'll repeat myself at the risk of being crude"

This appears to be the typical owner fixing stuff he has no legal right to fix, and no education, reference materials, or experience to fix it properly. Too often this evolves into a fix-everything-illegally attitude, and sooner or later something fails in flight because it wasn't fixed properly, and someone dies.

Electrical problems can result in electrical fires, or an electrical failure at night or in IMC or in congested airspace. No lights, no radios, no turn coordinator, no pitot heat, no nothing electrical. Fuel leaks improperly fixed can kill the engine. People use RTV on leaking fitting threads, and pay the price when it breaks free inside and clogs something. Hydraulic stuff improperly fixed can result in no brakes, or gear extension if applicable. Flight and engine controls improperly fixed can result in control system failure, or controls so badly misrigged that stall behavior becomes dangerous, or flutter occurs, or the engine doesn't run reliably: misrigged carb heat or mixture or idle mix. I've even found the throttle misrigged. Magnetos fooled with can fail abruptly.

There is a long history of aviation that reveals why education and training and experience and exams are required to get a mechanic's certification. These laws are written with the blood of a lot of people.
It seems OP is not really familiar with the system.

This could be an excellent example of “ Owner assist” IF ( repeat IF) done properly.

#1 Start with contacting an experienced Tech that is familiar with gens. Not all are.

There are various checks that can be performed that the Tech can provide guidance with.

FaceTime or Skype maybe useful here.

Please note that ALL avionics and lights should be OFF during the tests.

A smoking Avionics Suite can cost a LOT more than the Tech’s bill!
Once the circuit breaker pops it’s time to go to a reputable electrical shop. Could be as simple as a worn out breaker or more serious problems.
Pretty easy to take the generator off and have it tested. Brushes do wear on these and are a common replacement item. Are you using the old mechanical voltage regulator or one of the newer electronic ones? There are some really good troubleshooting notes on the Zeftronics web site. You're going to need a voltmeter.

Having said this, I've found that 90% of my electrical issues over the past 20 years were NOT due to the major components in the system. If you have a generator, your airplane is most likely > 60 years old. The switches, breakers and wiring are common culprits. Check those carefully first.

Generator belt slipping due to high charging load.

I've had this happen the automotive world. The car would run fine during the day. At night, and on the interstate, with the headlights on, the battery would discharge and not keep up with the total load, and the lights got dimmer and dimmer... Periodically I would have to pull over to the curb, fast idle the car for 15 minutes or so, then drive like the wind until it got too dark again. Lather, rinse repeat.

The next morning I found a very loose belt on the alternator. I replaced it, tensioned it according to specs, and it was fine thereafter. It was astounding to me how tight the belt was supposed to be!

Depending on the plane, which frequently use old automotive generators and alternators in them, this could have been the problem. Check the belt tension. If it is too loose, replace it (it is probably crazed due to scuffing) and tension it according to specs.