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08-27-2016, 01:56 PM
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Join Date: Jan 2015
Location: Oklahoma City, OK
Posts: 533
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Need Help - Low voltage and negative amps
I went to fly to a YE event and after starting I got a low EFIS voltage warning and negative amp reading on my GRT EIS/EFIS. This is the second time it's happened to me this month. The first time it happened (last time I flew) I cleared the problem by shuting down the engine and restarting. I tried this again but there wasn't enough battery left for a restart. I pushed it back into the hanger and put the battery minder on it.
Thirty minutes later I checked the battery voltage and it was 13.58. A friend suggested with this voltage reading on the battery so quickly after hooking up the battery minder that it probably wasn't the battery. He suggested I pulled the alternator and have it tested. I have the alternator off now (quite the job) and will have it tested but if it checks good what should I check next?
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Jim Harris, ATP, T38, EC/KC-135A/E/R, 2008 RV7A, 2nd owner, N523RM (2015)
Superior XPIO-360, Hartzel CS prop, Aerotronics panel with Dual GRT Horizon WS, EIS, Garmin 340, 335 w/WAAS gps, Dual 430s (non-WAAS), TruTrak 385 A/P with auto-level, Electric trim, Tosten 6 button Military Grips, FlightBox wired to WS, Dynon D10A w/battery backup, 406 MHz ELT. Custom Interior, New TS Flightline hoses, Great POH!
Retired - Living the dream - going broke! 
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08-27-2016, 03:39 PM
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Join Date: Jan 2015
Location: Oklahoma City, OK
Posts: 533
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It looks like it's a Plane Power Alternator
I've been reading various posts about PP alternator failures. My plane has 250.5 hours on it and that appears (from various other posts) to be the mean failure time for PP alternators. I also read that it may not be a good idea to have an automotive alternator shop repair it. Looking at pictures of PP alternators on Aircraft Spruce, it appears that is the one I took off my RV7A.
I also read that B&C alternators seem to holdup better. Any idea which model I should order? My current one has a built in regulator and is 60 amps.
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Jim Harris, ATP, T38, EC/KC-135A/E/R, 2008 RV7A, 2nd owner, N523RM (2015)
Superior XPIO-360, Hartzel CS prop, Aerotronics panel with Dual GRT Horizon WS, EIS, Garmin 340, 335 w/WAAS gps, Dual 430s (non-WAAS), TruTrak 385 A/P with auto-level, Electric trim, Tosten 6 button Military Grips, FlightBox wired to WS, Dynon D10A w/battery backup, 406 MHz ELT. Custom Interior, New TS Flightline hoses, Great POH!
Retired - Living the dream - going broke!
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08-27-2016, 04:21 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,667
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Good move replacing with B&C, they have both 40 and 60 amp models available, unless you need the power of the 60 I'd go with the 40.
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Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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08-27-2016, 04:41 PM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,068
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Checking battery voltage soon after charging can give misleading readings. Wait for 12 or 24 hours after removing the charger before measuring battery voltage. After the battery is fully charged, I suggest that you do a capacity check on it. Connect an automotive headlight, measure the current, then time how long it takes the battery voltage to drop to 11 volts.
According to the chapter on batteries in Bob Nuckolls' book, a PC680 battery should run a 56 watt load (4.8 amps) for 3 hours, or a 43 watt load (3.7 amps) for 4 hours, or a 35 watt load (3 amps) for 5 hours.
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Joe Gores
RV-12 Flying
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08-27-2016, 06:36 PM
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Join Date: Jan 2005
Location: Hopkinsville, KY
Posts: 957
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Ground Wire
Also check your main ground wire from your battery or firewall going to your engine. Touch both ends to ensure that the terminals have not cracked.
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Bobby Hester - Builder/Pilot/A&P
Surfing the web from Hopkinsville, KY
N857BH RV7A XP-O360 - Garmin G3X ADS-B IN/OUT 2020 Compliant
Web site: http://www.newtech.com/bobbyhester/RVSite.htm
Dec. 2019 VAF donator - alot better than any magazine subscription
Last edited by bhester : 08-27-2016 at 06:38 PM.
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