Replacement Jabiru Voltage Regulator: Follow-up
Posted: Thu Aug 08, 2019 12:08 pmIn Nov 2017 my original Jabiru Voltage Regulator (the Kubota OEM unit) failed after approximately 3 yrs and 250 hrs in service. I replaced the Kubota with a Caltric model R11-2 voltage regulator. You can find the details of that replacement in my original post, below.
viewtopic.php?f=8&t=2059&p=30468#p30468
This unit worked well, and I especially liked the slightly increased charging voltage that kept my Odyssey batter topped off better than the old Kubota. However, the unit failed on me last weekend while out on a cross country flight, after approx. 150 hrs in service over 18 months of use. The unit apparently got VERY hot internally and melted the output area of the internal circuitry, so much that it liquefied some of the black potting resin and dripped a bit down the case. There was no fire, nor any apparent risk of one, but it did make a small mess and stink badly!
In the past we've discussed the need to keep regulators cool, and recommended things such as mounting the case to a good heat sink surface, using heat transfer paste, mounting the cooling fins vertically to promote convection, and even adding a blast tube or small 12v fan to the force air over the fins. My unit was well mounted to the battery box mounting bad, with fins oriented horizontally, and good airflow around it (but free convection only). I've since replaced the regulator with a like unit and added a 60mm 12volt cooling fan strapped to the heat sink fins. We'll see how this works, and how the fan holds up.
I'm not sure why the unit overheated. The battery was topped off before the flight, and the voltage seemed normal for the 3 hr flight earlier in the day, so I don't believe the alternator was working especially hard to recharge a low battery. It's possible that when I taxi'd through a wet ramp on the way to the fuel pump that some water splashed up inside the cowl and got into something it shouldn't have. This seems unlikely, but it may not be coincidental that the very next full-power application after the water is when it died. The first indications of pending failure was an erratic rpm reading (the Dynon picks the tach signal off the alternator pigtail near the regulator); rpm jumped around for about 10 seconds until quitting all together, likely when the unit burned up. Interestingly, the voltage output remained at or below battery bus voltage (about 12 volts) the entire time, and the crowbar over-voltage protection system did not trip and take the alternator offline - as far as the crowbar was concerned, everything was working properly. When I lost RPM and saw the output voltage at 12 volts, I realized the problem and manually turned off the alternator switch.
Four conclusions come to mind from this experience. First, ensure you carry the spare parts you've identified to carry in your travel kit. I had both my charger and spare voltage regulator sitting in the hangar, where they did me no good. This was just going to be a quick day-trip, and I let myself become somewhat lax in my preparations. Second, erratic rpm readings might suggest an imminent alternator or voltage regulator failure, and it might be a good idea to immediately take the alternator offline to stop the failure in its tracks (maybe, maybe not). Third, know how long your battery will power your electrical needs without the alternator working. I had an estimate of this, but I had never tested it in actual use. After the regulator quit is was not very comforting to have any hard numbers to go on. I plan to do a full-up actual timed test to see how long my battery will keep things running at a typical flight load. Finally, I really am looking forward to buying one of the new B&C PM alternator voltage regulators that should be out in the next couple months. I spoke to B&C at AirVenture, and they promised them soon!
Jeff
viewtopic.php?f=8&t=2059&p=30468#p30468
This unit worked well, and I especially liked the slightly increased charging voltage that kept my Odyssey batter topped off better than the old Kubota. However, the unit failed on me last weekend while out on a cross country flight, after approx. 150 hrs in service over 18 months of use. The unit apparently got VERY hot internally and melted the output area of the internal circuitry, so much that it liquefied some of the black potting resin and dripped a bit down the case. There was no fire, nor any apparent risk of one, but it did make a small mess and stink badly!
In the past we've discussed the need to keep regulators cool, and recommended things such as mounting the case to a good heat sink surface, using heat transfer paste, mounting the cooling fins vertically to promote convection, and even adding a blast tube or small 12v fan to the force air over the fins. My unit was well mounted to the battery box mounting bad, with fins oriented horizontally, and good airflow around it (but free convection only). I've since replaced the regulator with a like unit and added a 60mm 12volt cooling fan strapped to the heat sink fins. We'll see how this works, and how the fan holds up.
I'm not sure why the unit overheated. The battery was topped off before the flight, and the voltage seemed normal for the 3 hr flight earlier in the day, so I don't believe the alternator was working especially hard to recharge a low battery. It's possible that when I taxi'd through a wet ramp on the way to the fuel pump that some water splashed up inside the cowl and got into something it shouldn't have. This seems unlikely, but it may not be coincidental that the very next full-power application after the water is when it died. The first indications of pending failure was an erratic rpm reading (the Dynon picks the tach signal off the alternator pigtail near the regulator); rpm jumped around for about 10 seconds until quitting all together, likely when the unit burned up. Interestingly, the voltage output remained at or below battery bus voltage (about 12 volts) the entire time, and the crowbar over-voltage protection system did not trip and take the alternator offline - as far as the crowbar was concerned, everything was working properly. When I lost RPM and saw the output voltage at 12 volts, I realized the problem and manually turned off the alternator switch.
Four conclusions come to mind from this experience. First, ensure you carry the spare parts you've identified to carry in your travel kit. I had both my charger and spare voltage regulator sitting in the hangar, where they did me no good. This was just going to be a quick day-trip, and I let myself become somewhat lax in my preparations. Second, erratic rpm readings might suggest an imminent alternator or voltage regulator failure, and it might be a good idea to immediately take the alternator offline to stop the failure in its tracks (maybe, maybe not). Third, know how long your battery will power your electrical needs without the alternator working. I had an estimate of this, but I had never tested it in actual use. After the regulator quit is was not very comforting to have any hard numbers to go on. I plan to do a full-up actual timed test to see how long my battery will keep things running at a typical flight load. Finally, I really am looking forward to buying one of the new B&C PM alternator voltage regulators that should be out in the next couple months. I spoke to B&C at AirVenture, and they promised them soon!
Jeff