CB Problem

[AWC Jeff]

Working the tailwheel endorsement, the IP and I decided to make a short hop over the mountains, eat breakfast and do some pattern work and landings.
Landed, taxi to the fuel pump, put in a couple gallons, then taxi to tie down.
Crank the engine, get a half a rev, no more. Battery is dead. No indication of any electrical problem until then. No CB, including the GEN CB are popped.
OK, it's VFR, hazy from the wildfire smoke, but the tower at Mojave is closed, we can go NORDO. Get the airplane home.
Prop start, fly back to Mojave, still no popped CB's. It's Sunday, so I decide I'll work on the airplane next Saturday. I have a day job, and I'm not working in a tin hanger when it's 110+ in the afternoon.
Saturday, I take off the cowling, check all the wiring from end to end, while under the panel checking the GEN CB I push on it. It goes in and out, won't reset.
Isn't the first time I've seen a CB pop, but the button doesn't move, and it sure can make your day miserable. Glad the button popped out while the airplane was sitting idle for 5 days.

[Pilot DAR]

I have found CB's to be less than ideally reliable. They are the first thing I look for if there is a circuit problem. To make matters worse, the later model C 150's have a hidden, self resetting CB for the alternator field. If it opens, and does not reclose, you have no charging, and no indication, unless your keen eye notes an ammeter discharge. ..

I attended a Cessna aging aircraft presentation many years ago. Cessna had bought back two 400 series Cessnas, both of which had had long and tough careers. The presenter told us that the deterioration of the structure they had expected to see, really was not too much a concern. In both cases, it was wiring, and electric components which were in horrible condition. Though Cessna has implemented structural SID inspections, the real message was to rewire the whole plane when it is aged. I guess this is why brand new Cessnas have better wiring, and many ground wires.

Pilots, know your electrical systems, so you are more able to diagnose, and assist the mechanic in finding the fault. "It doesn't work." will mean a larger repair bill, than a detailed description of the failure, and description of fault checking you have already done, and your observations.

When I have CB's removed, if I don't replace them, I at least measure the current at which they pop. I find it's often half again the rated value.

[oggers]

When I have CB's removed, if I don't replace them, I at least measure the current at which they pop. I find it's often half again the rated value.

That is not surprising. The rated value is nominal. They should not pop at that. They will pop in a certain amount of time which is dependent on the degree of overload. The higher the current the quicker they will pop.