help Electrical problems

[Bobby]

Help
1978 Sundowner
The main breaker (50A) kept popping so I had the shop test eveything and we
concluded a week breaker so we replaced it with a new one from Beech. Went up
on a Night IFR pre Check ride with a new instructor, loaded everything up on
the first two flights, no problem. Then last night went up again and pop goes
the breaker. Instructor gets excited and had me retuned to base. We were up
less then an hour when the main breaker popped.
Shop said they loaded everything and it was only drawing 40 Amps and alt was
putting out fine.
Does anybody have any ideas on where to start looking?

Bobby
78 Sundowner
N5161M



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[Rellihan]

Please post a list of every single item that is being turned on during the load testing on the ground.

Had anything just been touched or changed shortly before the most recent circuit breaker pop? Had the transmit keey been pressed? Anything at all?

It is also very possible to get a bad breaker out of the box. What brand and model number did you get and install?

[ChuzBear]

Bobby,
Some detective work is in store, as well as some very fine inspections.
Start at the CB and work back toward the equipment tied into it. Look for
burnt or charred residue on the wiring or the frame. It sounds to me like an
intermittent problem...a loose wire or hot lead making contact with a ground
somewhere along the route. Check connections first. 78 Sundowner? Wires are
nearly 30 years old and the insulation could be getting brittle and cracking
allowing a short to ground at a connection or within a wiring bundle. If on
preliminary inspection, nothing is obvious, you may want to untie your wiring ties
and separate wires; again checking for discoloration, cracks in the
insulation, or charring as a result of arcing. Since it happens in flight, my guess is
it is something loose or rubbing from the vibration.
On the other hand, it could be a faulty CB. Just because it is new,
don't rule it out; especially since the draw on the system is only 40 amps.
Disconnect your battery at the battery terminal BEFORE starting this
and, of course, remove your rings and watch. You'll be surprised how quickly
cracks in the wiring show up when you're moving wires around and your wedding
band makes contact. 40 amps will probably do more than char your ring and
discolor your finger and what it does to the LED in your watch...it will burn
bright, for a moment. But, unlike an analog watch, it won't even be right twice a
day <grin>.
Good luck,
Chuz


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[WA2EDN]

My landing light CB used to pop all the time after about 5 mins or op, then
every min or so.

Replaced the breaker (after checking the bulb wattage and wiring) and all is
well. CBs do go soft after a while especially when operating near the trip
current.
Dr Bill
76 Sundonwer
N9230S



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[vhcfy]

Does anybody have any ideas on where to start looking?

[AP: ] [AP] No but lots of sympathy. Goint through similar at the
moment. Painful, expensive and slow.

-ALlan Palmer
Brisbane, Australia


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