CenterHillAg
PATRON
Texas Coast
Curious if anyone is familiar with the older charging systems on the PT6. I have a turbine Ag Cat with the Mills PT6 conversion, which is essentially the firewall forward off an early King Air. The charging system consists of the starter generator, and the ancient reverse current relay and voltage regulator that have been around since WWII.
The plane was completely rewired in 2014 and everything is very well done and good grounds. I put a new engine on it this year and put a overhauled starter generator, new battery, plus an EI voltmeter/ammeter. The voltage would either show 24 volts and discharging, or turn the voltage regulator one click and it would go to 31 volts and overvolt. Changed the voltage regulator and it seemed to settle in at 27-28 volts on the test flight, but once I started working the volts would drop to 24.5 and the discharge light on the EI gauge would come on, but the generator warning light on the dash was still off. You could cycle the generator switch and it would start charging again, but after a few minutes it would start discharging. Here’s the kicker, once you’ve been flying a couple hours and everything is warm and the air conditioner is running, it’ll charge at 27.8 all day with no issues.
My mechanic thinks the EI gauge is just too sensitive and as long as the voltage is showing over 24 it’s ok, but admittedly he isn’t real familiar with this style of charging system, and I don’t like that answer. The voltage at startup the next day is 24.8 when the system is giving me fits, compared to 25.3 if the system has been charging normally. That’s a difference of 30 degrees on the ITT at start, still well below redline but the cooler the better. Is the solution just to run with all the lights, gps, ac, etc. on to keep a load on the charging system at all times and cycle the generator switch as needed to keep it charging, or is there something else I’m missing? I have a reverse current relay on the shelf I can install, I just don’t know if it could be the source of the intermittent issues.
Thanks for any help you might have.
The plane was completely rewired in 2014 and everything is very well done and good grounds. I put a new engine on it this year and put a overhauled starter generator, new battery, plus an EI voltmeter/ammeter. The voltage would either show 24 volts and discharging, or turn the voltage regulator one click and it would go to 31 volts and overvolt. Changed the voltage regulator and it seemed to settle in at 27-28 volts on the test flight, but once I started working the volts would drop to 24.5 and the discharge light on the EI gauge would come on, but the generator warning light on the dash was still off. You could cycle the generator switch and it would start charging again, but after a few minutes it would start discharging. Here’s the kicker, once you’ve been flying a couple hours and everything is warm and the air conditioner is running, it’ll charge at 27.8 all day with no issues.
My mechanic thinks the EI gauge is just too sensitive and as long as the voltage is showing over 24 it’s ok, but admittedly he isn’t real familiar with this style of charging system, and I don’t like that answer. The voltage at startup the next day is 24.8 when the system is giving me fits, compared to 25.3 if the system has been charging normally. That’s a difference of 30 degrees on the ITT at start, still well below redline but the cooler the better. Is the solution just to run with all the lights, gps, ac, etc. on to keep a load on the charging system at all times and cycle the generator switch as needed to keep it charging, or is there something else I’m missing? I have a reverse current relay on the shelf I can install, I just don’t know if it could be the source of the intermittent issues.
Thanks for any help you might have.