Loose connections, no individual ground, high heat location (put a temp strip on it, it's cheap insurance) under and over loading the VR.
I'm sure a couple of people here can throw in a few other reasons.
My temp on my VR has never gone over 145F and it's now 10 years old. I also placed temp strips on my ignition modules. It's the only way to be sure and not guess.
Roger Lee LSRM-A & Rotax Instructor & Rotax IRC Tucson, AZ Ryan Airfield (KRYN) 520-349-7056 Cell
Roger, can you please define "under loading" and explain why that would be bad for the RR? Over loading being a problem is easy to understand, but under loading?
Ken Ryan, you asked about my regulator conditions:
Normal in flight load - 4-5 amps
Start-up & taxi load - 8-10 amps (until battery is fully charged). I always keep the idle at 2000+ rpm.
Average flight duration - 1.5-3 hrs
Air Temp at Regulator - Have not measured, but it is mounted in the cockpit behind the panel, not near any hot component. Would guess about 85-90 F on a warm day.
After my last failure I cut a little hole in an air vent duct to blow some outside air towards the regulator. Will see if that helps.
My point is that even if you can extend the life by doing all the proper things that Roger and others have mentioned, it should not be necessary to go to that extent. I have never heard of any other aircraft regulator that needs this kind of kid glove treatment and still leaves you with a feeling that you can't trust it for an extended trip.
Modifications based on anecdotal evidence will do noting to resolve the failure rate. The first step in fixing the regulator problem is identifying what is failing in the regulator. My findings show there are two failure modes, based on the version of the regulator.
The older pre 2010 regulators fail from the inability to adequately transfer heat from the diode assembly to the case. This causes the diodes to unsolder themselves from the assembly. This is less of an issue if the application does not demand a lot of power from the charging system. Additional cooling may help in some applications. But, it doesn't matter how much you cool the regulator if the weak link is getting the internal heat out to the case.
Current production since 2010 uses a different diode package. This resolved the internal heat sinking issue of the older regulator versions. Unfortunately at this time they changed to gel type potting compound. All the examined failures of this version are caused by vibration. Vibration is causing failed solder connections at the SCRs and bridge rectifier. These components are rigidly attached to the case but the PCB floats in the gel potting compound. This failure is unique to the regulators with the new gel potting compound, this failure mode is nonexistent on the older versions.
Rotax does not believe a problem exists. They continue to blame the aircraft manufactures and owner/operators.
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