Omega232Devils
Well Known Member
I am writing this post in hopes that one day someone troubleshooting an alternator issue will find it and it will save them time and keep them from pulling their hair out. I used VAF archives and was able to find a solution to my problem.
Background:
RV-6A with Lyc O-360-A1A, 909.3TTSN, dual P-Mags, Hartzell CS prop, VM1000 engine monitor, seperate master and field switches, EXP2 Bus Module.
Problem:
Alternator has worked solid for the 3.5 years I have owned the plane. All records indicate it is the original alternator Mitsubishi A1T40791 50amp. Voltage has read between 14.1-14.4 over the years. Gradually creeping higher. (Quick talk with my A&P after solution found and I have learned this is high! oops)
Last Thursday coming home from a breakfast run, the alternator voltage began to fluctuate between battery power and 13.8. I began to troubleshoot.
On subsequent check flights the alternator would work great through ground checks, but as soon as takeoff power was applied it would die and I would be on battery power alone. (No fluctuations)
Troubleshooting:
I downloaded the plane power alternator troubleshooting guide as well as an electrical system troubleshooting guide (I did not build my plane). At first all signs pointed to my alternator (ie. 12V on power wire and 12v on field wire when activated via field switch). So, off comes the alternator and a quick stop at PepBoys for a bench test. Alternator tested GOOD! Now what?
I re-installed, shot some more wires and all appeared good. So I replaced all the electrical butt connectors on my system thinking that maybe the vibration of takeoff power was causing a short. This did not fix my problem. This goes on and on for 2 more days until I replace my field wiring completely. Still did not fix my problem. All signs still pointed to the alternator, so off it comes again and away to O'Reilly's autoparts I go. Bench tested GOOD, AGAIN!
Solution:
After some additional research on VAF, I came across and old post here describing an issue with the EXP2 and an over-voltage protection circuit. I had not thought of that. So I began to learn more about my EXP2 system and sure enough, a high voltage will cause the system to shut off the alternator input and requires a reset via the master switch to take it out of over voltage protection. (This is starting to sound familiar, alternator putting out 14.4v till full power is applied, then shuts off.)
With very little hair left and my guess that the alternator is original (1999) and has served the plane for over 900+ hours it is time for a new one. If it didn't fix the problem, it wouldn't hurt it. I was a little sketchy putting down $88.77 for a new alternator (Ultima 14694) when the core I was trading in had passed two bench tests. However, I installed the new alternator and she is humming right along at 13.6-13.8v. (More normal readings I have come to learn).
OBTW:
-Neither store could tell me at what RPM they ran the bench test.
-I now have a lifetime warranty on my '1985 Mitsubishi Mirage' alternator
-Car alternators have less strict tolerances for voltage output. (This may be also linked to internal regulators)
Dan
Background:
RV-6A with Lyc O-360-A1A, 909.3TTSN, dual P-Mags, Hartzell CS prop, VM1000 engine monitor, seperate master and field switches, EXP2 Bus Module.
Problem:
Alternator has worked solid for the 3.5 years I have owned the plane. All records indicate it is the original alternator Mitsubishi A1T40791 50amp. Voltage has read between 14.1-14.4 over the years. Gradually creeping higher. (Quick talk with my A&P after solution found and I have learned this is high! oops)
Last Thursday coming home from a breakfast run, the alternator voltage began to fluctuate between battery power and 13.8. I began to troubleshoot.
On subsequent check flights the alternator would work great through ground checks, but as soon as takeoff power was applied it would die and I would be on battery power alone. (No fluctuations)
Troubleshooting:
I downloaded the plane power alternator troubleshooting guide as well as an electrical system troubleshooting guide (I did not build my plane). At first all signs pointed to my alternator (ie. 12V on power wire and 12v on field wire when activated via field switch). So, off comes the alternator and a quick stop at PepBoys for a bench test. Alternator tested GOOD! Now what?
I re-installed, shot some more wires and all appeared good. So I replaced all the electrical butt connectors on my system thinking that maybe the vibration of takeoff power was causing a short. This did not fix my problem. This goes on and on for 2 more days until I replace my field wiring completely. Still did not fix my problem. All signs still pointed to the alternator, so off it comes again and away to O'Reilly's autoparts I go. Bench tested GOOD, AGAIN!
Solution:
After some additional research on VAF, I came across and old post here describing an issue with the EXP2 and an over-voltage protection circuit. I had not thought of that. So I began to learn more about my EXP2 system and sure enough, a high voltage will cause the system to shut off the alternator input and requires a reset via the master switch to take it out of over voltage protection. (This is starting to sound familiar, alternator putting out 14.4v till full power is applied, then shuts off.)
With very little hair left and my guess that the alternator is original (1999) and has served the plane for over 900+ hours it is time for a new one. If it didn't fix the problem, it wouldn't hurt it. I was a little sketchy putting down $88.77 for a new alternator (Ultima 14694) when the core I was trading in had passed two bench tests. However, I installed the new alternator and she is humming right along at 13.6-13.8v. (More normal readings I have come to learn).
OBTW:
-Neither store could tell me at what RPM they ran the bench test.
-I now have a lifetime warranty on my '1985 Mitsubishi Mirage' alternator
-Car alternators have less strict tolerances for voltage output. (This may be also linked to internal regulators)
Dan