|
|
Have an alternator issue with my LNC2. Wondering if anyone has run across
this type of issue.
Symptoms
- Starting about 4-6 weeks ago the alternator field breaker (10A) has
been tripping after 20min or so of flight. Can immediately reset (within
5-10 seconds) and the alternator comes back on line everytime and will stay
on for another 15-30 minutes.
- External vibration tends to make it happen more quickly.
- When operating correctly, field current is 0.5 - 0.6A for 16A output
load and 1.3A for 50A output load (measured)
- 10A circuit breaker is not "weak". Tripped 15A ultra-fast blow fuse
in Fluke meter (put in series to make above measurement) and breaker didn't
trip
- Researched alternators over the weekend, found the Sacramento Sky Ranch
website, ran the static checks and everything's OK from that end.
- 9 months ago had the alternator field breaker trip once. Found primary
feed wire from the battery plus side had slowly chaffed against the ground
case of the voltage regulator (VR), causing a momentary battery short to
ground. Replaced the primary battery feed, improved the spacing, added better
wire insulation and never saw an issue again until 4 weeks ago (yes, checked
that and no sign of chaffing).
Equipment:
- Bosch 95A alternator, ~450 hours time in service (replaced the original
non-Bosch at ~100 hours when the PMA'd unit failed)
- External voltage reguator, single wire setup. May have an internal
OVP but not sure (should have the datasheet here on Wednesday)
- 10A field reaker feeds the VR high side input.
Some Ideas:
- Have checked all wiring from alternator to VR and have found no chaffed
wires.
- Checked the field wire from the alternator to the VR for intermittents
or shorts with DVM and didn't see any sign. Yep, did the wire giggling trick,
pulled, pushed and prodded but everything seemed solid.
- Alternator or VR (just behind firewall) could be getting heat soaked
but then would expect failure rate to increase as time goes on
- Could the momentary shorting of the +12V battery to the VR case have
weakened the main VR output regulating transistor?
- Pulling alternator and VR out as a pair and have them checked at our
local alternator/generator shop. Spoke with the owner (has over 45 years
experience with motors, alternators & generators) and the symptoms didn't
ring any bells.
Any other ideas out there?
Thanks,
jim...
N1222K
LNC2, 571 hours
(wow, didn't realize this ended up being such a ramble)
|
|