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First, I'm happy with the unit, 582 hours and 8 years before failure. Second, if anyone has a core unit they want to trash, please write me offline. I need a stator.
In the Legacy, I normally get low voltage on this unit until 1800 rpm or so. There have been some symptoms but nothing pointing to the alternator. This past weekend, the light stayed on with zero amps. Long story compressed, the wiring in the plane checked out, local shops can't spin the unit because of the fragile coupling so I put it on a drill and only got 8v. Out of warranty, I ordered a new one and decided this morning to look inside as these things are fairly standard. Field (rotor) windings were fine and amps checked out. Diodes all checked out. Stators never have a problem? When the cover was removed, the stator has three windings and a common terminal. Two of three stator leads were broken off and the the third tested open somewhere and is not repairable. I also found the rear bearing spinning in the case which isn't great because the bearing seems fine and it should have been a good press fit or otherwise firmly attached. The brushes are in good shape as is the rotor and drive bearing and coupling.
Vibration could be the culprit and this engine has had shakes for a while. Maybe this unit is part of the problem? Fortunately, they are not horribly expensive but as I spoke to Bill at B&C he had hoped to see 1700 hour life but this has multiple problems that would never make it that far. The failure mode on these stator wires suggests a problem so if your SD-20 fails or is intermittent, you can easily check these 4 wires for continuity. While I am not advising changing any parts, the diode packs, bearings and rear case parts are fairly easy to source. B&C makes STCd units so parts out the door is not permitted. Repairs on this unit would equal the cost of a new unit according to B&C which is too bad because a reasonable repair/overhaul is a good business model versus buy new. Photo one shows the stator with the common (three leads together) and only two of the three coil leads showing. The third broke off, one is open circuit and one is broken at the screw in the next photo. The second photo shows two of the stator wires that are screwed to the diode pack. One broken at the stator level and one broken at the screw itself. If anyone has a core, I'll pay shipping, get a bearing and put this on the shelf as a spare. Thanks, Paul, Legacy, Spruce Creek.
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