petehowell
Well Known Member
I need some help from the hive-mind......
RV-9A with 2700 hours. Coming back from fly in on Sat morning, noticed that Bus voltage was variable from 13.4 - 13.8. It's normally 14.1 - 14.3.
Equipment
- 87 Samurai 40 amp Int Reg alternator (this is #3 -they seem to last 800-1000 hrs)
- PC680 Battery 5ish yrs old
- 60 amp P&B breaker b/t the Alt B term and the main buss
Things I have done:
- Verified bus voltage at the F term on the alternator 12.8 with engine off
- snugged up the terminals in the ALT plug - they are tight(Just using the F and L terminal of the 3 prong plug.
- Swapped alt for a known good unit - no change
- Tested the battery at the parts store - passed as an AGM Batt with 220 CCA it is 12.7-12.8 at rest
- swapped out the battery for an older one that holds a charge well - no change. Battery connections are tight
- Ran a lead from the B term of the Alt to the cockpit - with engine running it is a solid 14.3 volts
- Used a VOM to verify the bus voltage actually is 13.4-13.6 volts (it is)
- Chased connections from the alt to the breaker and bus they seem to be solid(did not disassemble and clean any of them)
- Flew it near the field tonight - Same voltages, but noticed if I turned the lights on, the voltages actually would go up a bit to 13.8 and then return to ~13.6. However, if I then, shut off all the lights, the voltage would run up to 14.2 and stay there for a few min, then migrate back down to 13.6. Also, when I landed and shed the lights, AP and TPX, the volts would climb back above 14 for bit.
- Checked Voltage drop across the main contactor - negligible - snugged up the connections for giggles - nothing was loose.
- Checked voltages on both side of the 60 amp breaker they were same as bus volts. If i pulled the breaker while at idle - the volts on the feed side went to about 15.2 (I know this is not great for the alternator)
- Checked Ohms across the 60 amp breaker - negligible.
Thoughts:
- Alternator seems good - 14.3 at the output terminal
- There seems to be something causing a big load on the main bus, the battery comes to mind. I don't mind replacing it, but it does seem to be good, and had same behavior using 2 diff, albeit older batteries
- Bad connection? Undo and clean all the connections.
- Replace the 60amp breaker again - maybe it goes high resistance under high load?
- Replace the Master contactor
I'm kinda lost here - any thoughts appreciated!
RV-9A with 2700 hours. Coming back from fly in on Sat morning, noticed that Bus voltage was variable from 13.4 - 13.8. It's normally 14.1 - 14.3.
Equipment
- 87 Samurai 40 amp Int Reg alternator (this is #3 -they seem to last 800-1000 hrs)
- PC680 Battery 5ish yrs old
- 60 amp P&B breaker b/t the Alt B term and the main buss
Things I have done:
- Verified bus voltage at the F term on the alternator 12.8 with engine off
- snugged up the terminals in the ALT plug - they are tight(Just using the F and L terminal of the 3 prong plug.
- Swapped alt for a known good unit - no change
- Tested the battery at the parts store - passed as an AGM Batt with 220 CCA it is 12.7-12.8 at rest
- swapped out the battery for an older one that holds a charge well - no change. Battery connections are tight
- Ran a lead from the B term of the Alt to the cockpit - with engine running it is a solid 14.3 volts
- Used a VOM to verify the bus voltage actually is 13.4-13.6 volts (it is)
- Chased connections from the alt to the breaker and bus they seem to be solid(did not disassemble and clean any of them)
- Flew it near the field tonight - Same voltages, but noticed if I turned the lights on, the voltages actually would go up a bit to 13.8 and then return to ~13.6. However, if I then, shut off all the lights, the voltage would run up to 14.2 and stay there for a few min, then migrate back down to 13.6. Also, when I landed and shed the lights, AP and TPX, the volts would climb back above 14 for bit.
- Checked Voltage drop across the main contactor - negligible - snugged up the connections for giggles - nothing was loose.
- Checked voltages on both side of the 60 amp breaker they were same as bus volts. If i pulled the breaker while at idle - the volts on the feed side went to about 15.2 (I know this is not great for the alternator)
- Checked Ohms across the 60 amp breaker - negligible.
Thoughts:
- Alternator seems good - 14.3 at the output terminal
- There seems to be something causing a big load on the main bus, the battery comes to mind. I don't mind replacing it, but it does seem to be good, and had same behavior using 2 diff, albeit older batteries
- Bad connection? Undo and clean all the connections.
- Replace the 60amp breaker again - maybe it goes high resistance under high load?
- Replace the Master contactor
I'm kinda lost here - any thoughts appreciated!