Bill Boyd
Well Known Member
I had a little episode on a local flight Sunday where my Alt trouble light flickered several times, then stayed on full-brightness followed by an OV warning on my EIS, voltage climbed rapidly to 36V. I popped the Alternator side of the ol' Cessna split master immediately, and continued the flight on battery with a bus voltage of 12.1-12.2 All avionics thankfully worked normally. No smoke released. Especially glad the dual P-mags continued to function normally.
I tried turning on the landing lights to load the charging system and bringing the alternator back online, got 18 volts and climbing, immediately turned the alternator off again. Tried it one more time at lower engine rpm and got a normal 13-14V range that seemed stable, no alternator light. Decided that aloft was no place to troubleshoot a runaway alternator that hadn't (yet) smoked anything expensive, and landed.
Clearly an intermittent problem that went away again before I landed, and I obviously have one of the Denso IR alternators that is not (further) harmed by turning it on and off under load, something I had never done before. I strongly suspect a wiring connector or split master problem brought on by airframe age (20 years) and poor building practices in my younger years. However, it's possible the internal regulator is toast. I'm willing to troubleshoot and to try the remove-and-replace thing. A house fire has left me with no documentation of my electric system as-is. I think I built it per Vans electric plans and when I "upgraded" to the IR Denso unit I just removed the old Vans ER alternator, the Ford regulator, the AeroElectric home made OVP module and bolted the new IR alternator in. But without wire tracing (my next step) I'm not sure of the architecture I'm dealing with.
I have current copies of Z-11, which is likely the progenitor of my current rat's nest of wires, and also Interim Z-24 - which is definitely being added soon. Anyone have a reference to the schematic Van was recommending for basic electrics in the 1990's? I sure would like to take a peek at it, as it's probably what I put in to begin with. Maybe all I need to get flying again is a new master switch and some squeezed and potted connections to the alternator, but I know there will be lots of opinions and welcome advice forthcoming
I tried turning on the landing lights to load the charging system and bringing the alternator back online, got 18 volts and climbing, immediately turned the alternator off again. Tried it one more time at lower engine rpm and got a normal 13-14V range that seemed stable, no alternator light. Decided that aloft was no place to troubleshoot a runaway alternator that hadn't (yet) smoked anything expensive, and landed.
Clearly an intermittent problem that went away again before I landed, and I obviously have one of the Denso IR alternators that is not (further) harmed by turning it on and off under load, something I had never done before. I strongly suspect a wiring connector or split master problem brought on by airframe age (20 years) and poor building practices in my younger years. However, it's possible the internal regulator is toast. I'm willing to troubleshoot and to try the remove-and-replace thing. A house fire has left me with no documentation of my electric system as-is. I think I built it per Vans electric plans and when I "upgraded" to the IR Denso unit I just removed the old Vans ER alternator, the Ford regulator, the AeroElectric home made OVP module and bolted the new IR alternator in. But without wire tracing (my next step) I'm not sure of the architecture I'm dealing with.
I have current copies of Z-11, which is likely the progenitor of my current rat's nest of wires, and also Interim Z-24 - which is definitely being added soon. Anyone have a reference to the schematic Van was recommending for basic electrics in the 1990's? I sure would like to take a peek at it, as it's probably what I put in to begin with. Maybe all I need to get flying again is a new master switch and some squeezed and potted connections to the alternator, but I know there will be lots of opinions and welcome advice forthcoming