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10-07-2013, 08:54 PM
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Join Date: Sep 2012
Location: GA
Posts: 50
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Alternator field fault
I am getting a field fault on the alternator occasionally. The wire has been checked from end to end. The alternator has been bench checked twice. I can reset it on the VPX and it never recurs on the same flight. Airpower 60 amp. Output is normal when the field is not shorted.
It was doing this before the panel upgrade and VPX.
Any ideas?
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10-07-2013, 10:12 PM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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It's virtually impossible to diagnose electrical problems on internet forums, but I'll try.
Does your alternator have an overvoltage crowbar built in? If so, it may be tripping and shorting the field circuit.
You said you have an Airpower alternator, but is this actual brand or just the distributor?
__________________
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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10-08-2013, 06:34 AM
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Join Date: Sep 2012
Location: GA
Posts: 50
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Alternator fault
Whoops
AL12-EI60/B PlanePower alternator.
Yes I know it is nearly impossible to do over internet. I can't do it and I am standing here looking at it!
Just want to perform obvious checks before sending back to PlanePower for a real bench check.
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10-08-2013, 07:31 AM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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What do you have the field current set at? The PP alternator will draw a full 5A (and maybe a little more) when asked.
__________________
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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10-08-2013, 07:48 AM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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__________________
===========
V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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10-08-2013, 09:38 AM
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Join Date: Sep 2012
Location: GA
Posts: 50
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Field fault
Walt
Field amps are usually around 4.5 . I don't know that it is adjustable.
Vern
Very interesting thread. My fault generally occurs during run up. I reset and field is usually around 4.5 and output is 14.5 volts. I have not tested for over voltage protection. Thanks for info
Phil
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10-08-2013, 10:32 AM
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Join Date: May 2007
Location: Inver Grove Hgts, MN
Posts: 329
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Phil,
How is your field switch wired? I just finished a project here at SteinAir and Marc at Vertical Power told me to use the dedicated alternator field C/B in the VP, and to make sure to tie it to a switch input (not "always on"). The field switch on your panel then only provides a ground to close that VP switch. If you do it this way a field trip will annunciate "overvoltage" instead of "short circuit". It also insures full functionality of the VP with respect to the charging system. This may not solve the tripping problem but since your VP shows "short circuit" after a trip it's probably not wired the way Marc recommends.
__________________
Mike Hilger
RV-6 N207AM w/G3X, 1,600 hours +
South St. Paul, MN (KSGS)
A&P, EAA Tech Counselor
We're all here because we're not all there...
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10-08-2013, 03:07 PM
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Join Date: Sep 2012
Location: GA
Posts: 50
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Little knowledge
Thanks Mike. A little knowledge is dangerous snd I didn't
even have that much! Will check and fix it.
Phil
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10-08-2013, 08:14 PM
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Join Date: Sep 2009
Location: St. Louis, MO
Posts: 1,788
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Since this was happening pre VPX I would suggest that the over voltage crowbar is kicking in to soon and tripping the over current protection in the VPX. Sounds like the alternator is bad. The PP alternators have a built in over voltage crowbar. The crowbar shorts the field to ground when an over voltage condition exists. Thus tripping the field breaker.
__________________
Bill Peyton
RV-10 - 1125 hrs
N37CP
First Flight Oct 2012
Aviation Partners, LLC
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10-08-2013, 10:03 PM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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Quote:
Originally Posted by Bill.Peyton
Since this was happening pre VPX I would suggest that the over voltage crowbar is kicking in to soon and tripping the over current protection in the VPX. Sounds like the alternator is bad. The PP alternators have a built in over voltage crowbar. The crowbar shorts the field to ground when an over voltage condition exists. Thus tripping the field breaker.
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It's critical to make sure every connection in the field circuit is solid. Turn on the master, measure the voltage at the master bus then measure the voltage at the input to the field connector on the alternator. This is a bit tricky... you'll need to push the voltmeter probe into the back of the connector to intercept the terminal.
You should have less than 0.25 volt difference. Any more and you need to start looking for problems.
If this measures OK, then start looking into the alternator. It's possible to remove the alternator and build a bench tester like I did, but it's probably easier to remove the brush/regulator/ovp assembly and test it on the bench.
You'll need a current limited variable voltage power supply. Set the current limit to 1 amp and vary the voltage upwards starting at 12V. The OVP trip point should be around 17V. My failed OVP tripped at 13.8V.
This takes some electrical skills, so find the guy on the field named 'Sparky' and ask for help.
__________________
===========
V e r n. ====
=======
RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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