Needed to fly up to KGRB from KATW (10 min) to pick up some Camguard and warm things up for an oil change. Returning to KATW my wife and I decided to fly to lunch, so I stopped for gas at self-serve. After fueling, I cranked up to repo to hangar where my wife was waiting, and during the short taxi I noticed the distinct smell of burning rubber..not an acrid electrical burning smell. My braking was normal and there was adequate cooling during fueling, but I started looking for smoke for a brake fire or evidence I had a flat tire. I shut down at the hanger and popped out for a look, everything appeared normal and all systems were operating normally, so we continued to lunch because I thought the smell wasn't originating for my aircraft.
Mid-flight, I smelled the rubber burning smell again for a couple seconds and it went away. Everything indicated normal, and again looked normal after landing. I took an extra hard look around and in cowling and still nothing, because I was now convinced the smell was from my airplane. The totally confusing part was it smelled exactly like burning rubber...the smell you encounter when you're downwind of large aircraft touchdown. It did not smell electrical.
After lunch I returned back to KATW, but what I didn't notice is that my system voltage was battery voltage (~12.5) the entire flight (20 min). It wasn't until I stopped for gas again and restarted that I noticed cranking was different and saw there was no alternator output after start.
I changed my oil, and the next day attempted fixing the alternator. I initially thought it was bad regulator because mine is modified to receive field input only from the IGN wire. However, the problem ended up being a bad rectifier...it appears one of the diodes completely fried. I didn't save the part or take pictures, but it was burned up pretty good underneath, near the A stator output...assuming the diode in that spot? Luckily there's an alternator shop down the road and they had a rectifier in stock for $40. I changed it out and proper alternator output resumed.
Finally my question...what would cause this? I'm not a fan of things burning in flight and wondering if there's another root-level problem. The auto electric shop thought it was a weak battery or high resistance somewhere causing the rectifier to heat up. Though this doesn't seem to be the case...I was able to do two starts and fly almost 30 minutes with only 0.1v drop in voltage, and as indicated by the G3X graph, the charge recovery is looks quick and the loads all look normal prior to failure. The only thing that is different recently is the installation of a IBBS, but that and every other system is operating normally.
I've attached the Volts and Amps reading from the G3X...first picture shows the point in flight where I smelled burning rubber...you can see the voltage drop below normal battery voltage and amps go to -39 indicating a significant load on the battery originating from the alternator (my Hall effect sensor is installed on the B+ lead), but then recovery eventually to normal volts and amps. The second picture shows the beginning of the flight home where only battery voltage is indicated and the cursor pointing to the voltage drop during the start.
Thoughts?
Mid-flight, I smelled the rubber burning smell again for a couple seconds and it went away. Everything indicated normal, and again looked normal after landing. I took an extra hard look around and in cowling and still nothing, because I was now convinced the smell was from my airplane. The totally confusing part was it smelled exactly like burning rubber...the smell you encounter when you're downwind of large aircraft touchdown. It did not smell electrical.
After lunch I returned back to KATW, but what I didn't notice is that my system voltage was battery voltage (~12.5) the entire flight (20 min). It wasn't until I stopped for gas again and restarted that I noticed cranking was different and saw there was no alternator output after start.
I changed my oil, and the next day attempted fixing the alternator. I initially thought it was bad regulator because mine is modified to receive field input only from the IGN wire. However, the problem ended up being a bad rectifier...it appears one of the diodes completely fried. I didn't save the part or take pictures, but it was burned up pretty good underneath, near the A stator output...assuming the diode in that spot? Luckily there's an alternator shop down the road and they had a rectifier in stock for $40. I changed it out and proper alternator output resumed.
Finally my question...what would cause this? I'm not a fan of things burning in flight and wondering if there's another root-level problem. The auto electric shop thought it was a weak battery or high resistance somewhere causing the rectifier to heat up. Though this doesn't seem to be the case...I was able to do two starts and fly almost 30 minutes with only 0.1v drop in voltage, and as indicated by the G3X graph, the charge recovery is looks quick and the loads all look normal prior to failure. The only thing that is different recently is the installation of a IBBS, but that and every other system is operating normally.
I've attached the Volts and Amps reading from the G3X...first picture shows the point in flight where I smelled burning rubber...you can see the voltage drop below normal battery voltage and amps go to -39 indicating a significant load on the battery originating from the alternator (my Hall effect sensor is installed on the B+ lead), but then recovery eventually to normal volts and amps. The second picture shows the beginning of the flight home where only battery voltage is indicated and the cursor pointing to the voltage drop during the start.
Thoughts?