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recapen(at)earthlink.net
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 Posted: Tue Feb 05, 2013 5:23 am Post subject: SD-20 Alternator / SB1B-14 regulator failure modes |
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Looking to see if anyone has ever experienced a failure of either of these two types of units. This is a backup unit be design so a failure might not get noticed - until you need it. My start-up checklist has me powering on the backup unit first, checking for amps generated and the warning light on...then power up the primary unit - I get more amps and the secondary light goes out...
Not looking to bad-mouth anyone.....my back-up alternator did not come on-line during my start-up checklist. No biggie - I was going on a local VFR fun flight close enough to get back to home-plate if necessary. Anyone experienced anything with theirs - how did it present? what was the cause? How did you determine / diagnose? What did you do to repair?
My line of troubleshooting thinking has me first checking to make sure the unit turns when the engine turns - then looking at the two ckt breakers and finally testing for current at the field wire on the back of the alternator.
Thanks,
Ralph Capen
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RV7ASask
Joined: 25 Jan 2006
Posts: 36
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| Posted: Tue Feb 05, 2013 7:43 am Post subject: Re: SD-20 Alternator / SB1B-14 regulator failure modes |
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Ralph,
I have an SD-20/SB1B-14 as a back-up unit with a Z12 architecture. I had an anomaly early on where, on my after start check, I would have both alternators selected ON. With everything stable at a low load and the main alternator pulling around 8 amps, I would select the main alternator OFF. The Aux would come on line and the amps would increase up to 16 amps.
After much sleuthing by this great team on the Aeroelectric List I changed the Aux alternator shunt and replaced the original supplied 40 amp shunt with a 60 amp shunt and now all is well.
I still do the same check in the 'After Start' but the amp reading remains the same on both alternators.
Regards
David Lamb
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recapen(at)earthlink.net
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| Posted: Mon Feb 11, 2013 12:04 pm Post subject: SD-20 Alternator / SB1B-14 regulator failure modes |
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As a follow up to my recent failure.
The issue ended up being the gear coupling in the alternator.
The gear coupling is a field replaceable item and I have one on the way.
More when it happens....
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