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  #1  
Old 07-08-2021, 11:34 PM
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werxcv01 werxcv01 is offline
 
Join Date: Aug 2008
Location: Brandon, MS
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Default Failing alternator? Or just undersized?

Iíve been practicing cruising at 90 knots at 1,800 feet in my RV-8 with a Lycoming O-360, fixed pitch prop, and 30 amp alternator. The airplane has a VFR GRT Sport EFIS, single radio, ADS-B transponder, autopilot, and a full set of EI gauges.

The best RPM is about 1720, but with the strobes, nav lights, and landing and taxi lights on, I am getting a discharge light and the voltage is showing 12.2 to 12.4 volts.

Iím concerned about discharging the battery on the Ripon approach. Could this mean my alternator is going out?

A new alternator is on the AirVenture shopping list.
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  #2  
Old 07-08-2021, 11:46 PM
BobTurner BobTurner is offline
 
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Certainly doesnít look good. If you use higher rpm and turn off the lights, does the buss voltage get up to 14 volts? If no, you have a problem.
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  #3  
Old 07-09-2021, 04:26 AM
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Did the problem just start? Some lights pull a lot of power - are yours LEDs or incandescent?
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  #4  
Old 07-09-2021, 05:35 AM
swordtail swordtail is offline
 
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I would resolve that electrical problem before you put yourself in a hectic environment under a heavy mental load. Your head will be rocking like a bobble head doll just doing the approach.
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  #5  
Old 07-09-2021, 06:07 AM
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werxcv01 werxcv01 is offline
 
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This did not just start, just became more noticeable during these practice flights. The lights are incandescent, maybe halogen for the landing and taxi light. Normal flights with all lights on during the descent keep the battery charged.

Iíve flown the approach in other aircraft six or seven times, so hopefully know what to expect. My plan is to arrive early afternoon the Friday before the show.
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  #6  
Old 07-09-2021, 06:20 AM
BillL BillL is offline
 
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Location: Central IL
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Some information is in order . . . to facilitate diagnosis.

Alternator rating.
Amps being drawn.
voltage in normal conditions (is it being regulated normally?)
Has the belt tension been set by the drag torque method?

You will probably draw a conclusion for your self with this in hand. Grossly, if it is producing 14.2-14.5v normally and not slipping, then it is overloaded.

More detailed information could be gained by measurement of the field amps, and voltage under normal and approach loading if the rating is high but amps are lower.
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  #7  
Old 07-09-2021, 06:40 AM
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werxcv01 werxcv01 is offline
 
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We replaced the alternator belt during the 2020 condition inspection. I work with an experienced A/P-I/A so trusted him to set the tension and then check it during the 2021 inspection completed in May. The alternator and voltage regulator were replaced at 410 tach hours in 2014. The current tach time is about 640.

The voltage usually settles just below 14 volts. The amperage usage seems to fluctuate from 11 to the high teens, low twenties. I usually just fly with the strobes on, as I currently fly day VFR.
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  #8  
Old 07-09-2021, 07:01 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by werxcv01 View Post

The voltage usually settles just below 14 volts. The amperage usage seems to fluctuate from 11 to the high teens, low twenties. I usually just fly with the strobes on, as I currently fly day VFR.
an alternator should be producing it's max output somewhere in the neighborhood of 2000 RPM, depending upon flywheel type. What did the ammeter read on the practice flight with the low voltage? If it gets to the low 20's without nav and landing ligths, I would not expect the load with both incandescent nav and landing lights on to be under 30 amps, so results not surprising. Using landing lights at OSH makes sense, but I don't see nav lights helping much in daytime recognition. I bet those are drawing at least 5 amps.

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Last edited by lr172 : 07-09-2021 at 07:06 AM.
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  #9  
Old 07-09-2021, 08:29 AM
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rv6ejguy rv6ejguy is offline
 
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I tested my 70A ND alternator. Produced 26 amps at 1500 rotor rpm, 60 amps at 2800 rotor rpm. Given the typical drive ratio on a Lycoming setup, I'd guess you should have at least 90% of the full output at 1700 engine rpm.
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  #10  
Old 07-09-2021, 08:36 AM
rick9mjn rick9mjn is offline
 
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first;;;; you derisive a grade of A+ , for practicing flying, some parts, of flying into OSK , and i back up the idea, from the poster #5 saying ""but I don't see nav lights helping much in daytime recognition. I bet those are drawing at least 5 amps.
good day and good job on your practicing / rick
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