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11-25-2008, 11:43 AM
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Join Date: Nov 2007
Location: Paris ( France )
Posts: 38
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Serious electrical problem
Hello to all,
Ready to start engine for the first time and had removed the battery for a final charging.( an Odyssey 680 ).I asked a friend to reinstall the battery when it was ready as I had to leave for a few hours. When I came back I did a quick check and everything looked normal so I switched on the master/battery switch to check cockpit lights and indications. I was suprised to see that the instrument panel warning lights were quite dim and indicated voltage was only about 12.5 V , the ammeter on the other hand indicated +30 A and the alternator breaker (60A) had tripped !!.
I immediately switched the battery switch off and checked the engine and battery -- I found the battery connections reversed !!.
As you can imagine my first engine run will not take place today.
Does anybody know what damage has been done to my electrical system in general and my instruments in particular.?
I have a basic Vans electrical system with Vans "steam " instruments. Radios etc. are on an avionics switched supply,which was off at the time. Alternator is an ND 35A model.
How could the master relay close with reversed polarity and allow power to trip the 60A alternator breaker?
Any help and information would be much appreciated
Mike
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11-25-2008, 11:55 AM
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Join Date: Nov 2006
Location: Boise, ID
Posts: 1,095
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Quote:
Originally Posted by tullow
Hello to all,
Ready to start engine for the first time and had removed the battery for a final charging.( an Odyssey 680 ).I asked a friend to reinstall the battery when it was ready as I had to leave for a few hours. When I came back I did a quick check and everything looked normal so I switched on the master/battery switch to check cockpit lights and indications. I was suprised to see that the instrument panel warning lights were quite dim and indicated voltage was only about 12.5 V , the ammeter on the other hand indicated +30 A and the alternator breaker (60A) had tripped !!.
I immediately switched the battery switch off and checked the engine and battery -- I found the battery connections reversed !!.
As you can imagine my first engine run will not take place today.
Does anybody know what damage has been done to my electrical system in general and my instruments in particular.?
I have a basic Vans electrical system with Vans "steam " instruments. Radios etc. are on an avionics switched supply,which was off at the time. Alternator is an ND 35A model.
How could the master relay close with reversed polarity and allow power to trip the 60A alternator breaker?
Any help and information would be much appreciated
Mike
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Hi Mike,
The master relay is pulled closed with a small wire wound electro-magnet. Any current flowing through it (forwards or backwards) will generate a magnetic field and pull it closed. Without looking at all of your instrument schematics, it's hard to say whether they're damaged, but some should have some type of circuit protection for this kind of thing. Even if they didn't, I'm not sure any damage would occur.
If it were my airplane, I would reconnect the battery properly and turn everything on one at a time. If it works, then move on. I would perform an electrical system check if everything works and call it good. Just my 2 cents.
__________________
Sonny W
Boise, Idaho
RV-7A Flying!
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11-25-2008, 12:04 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,687
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You'll just have to hook it up correctly and start checking things. I can almost assure you all the Van's gauges are toast as they have no polarity protection. The alt "may" be ok, other things like spike diodes across relays (like the master contactor) will also be fried. Master contactors don't care about polarity so they will pull hooked up either way. I would call it a "minor" setback since the avionics (expensive) stuff is ok 
__________________
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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11-25-2008, 12:10 PM
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Join Date: Apr 2007
Location: -
Posts: 502
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Consider yourself very luck that your avionics were all isolated. A few of them probably would not have lived to tell the tale.
As an electrical engineer, I second the idea of just fixing the polarity and turning it back on in a progressive fashion. Thats probably the best way to discover any problems, and its unlikely you'll cause any further damage. If everything seems to still work --- fire it up!
-DC
Last edited by digidocs : 11-25-2008 at 12:12 PM.
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11-25-2008, 04:22 PM
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Join Date: Nov 2007
Location: Paris ( France )
Posts: 38
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Well thanks for your advice,
I've just spent the last couple of hours at the hangar ( it's now past midnight here) and as you suggested I connected the battery correctly and find that my ammeter,voltmeter,manifold pressure and fuel guages work normally,so my fingers are crossed for the other Vans instruments on the panel. The avionics are all ok as they are on a separate switched power supply.
So not as bad as I initially feared, must get some sleep now and up to the hangar tomorrow to check out the rest,
Thanks again to those of you who replied to my question
best regards
Mike
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11-25-2008, 04:39 PM
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Join Date: Jan 2008
Location: Delaware
Posts: 79
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A couple of ways to prevent a reoccurance....Make the battery leads short enough that if the battery is installed in the box backwards they won't reach the terminals. Has anyone installed a diode in series with the master switch to prevent the master relay from energizing if the battery is backasward?
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11-25-2008, 05:13 PM
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Join Date: Jul 2007
Location: Keller, TX
Posts: 1,553
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replacement guages
I'm pulling my Vans engine guages out to put in an EIS-4000. Let me know if you need a replacement!
__________________
RV-8 180 hp IO-360 N247TD with 10" SkyView!
VAF Donations Made 8/2019 and 12/2019
"Cum omni alio deficiente, ludere mortuis."
(When all else fails, play dead.)
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11-25-2008, 06:28 PM
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Join Date: Jul 2006
Location: Houston, TX
Posts: 208
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Alternator toast?
The Vans (Ispro) gauges have a reverse polarity protection diode inside so they should be OK. While not all of the current paths are after the diode, they are through resistors which should make it OK.
On an alternator, reverse polarity will usually toast the diode packs, opening one or more diodes. When this happens, one or more of the 3 phazes will be inoperative. This condition can be misleading as under light loads the alternator can appear to carry the load with a phaze missing but not for long. If it seems that the alt survived, you should do a load test. Also, some outfits sell a cigarette lighter affair that looks for missing phazes in the alternator output (looks at the ripple voltage) as well as low volts etc. but if it were my plane, I'd pull it off and replace it (or have it rebuilt with new diode packs). The breaker popped because some of the diodes carried essentially everything the battery had to offer for as long as the breaker took to open.
Personally, I'd also replace any other diodes across solenoids etc. You could do a detailed analysis but those are cheap.
Glad you didn't have the avionics on.
__________________
John Oldenkamp
RV-7A project for sale 
VAF Paid 2018
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11-25-2008, 06:37 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Or at least some...
Quote:
Originally Posted by CESSNADON
A couple of ways to prevent a reoccurance....Make the battery leads short enough that if the battery is installed in the box backwards they won't reach the terminals. ....
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.... RED and BLACK heat shrink to color code the battery wires.
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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11-25-2008, 06:58 PM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,769
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Quote:
Originally Posted by az_gila
....RED and BLACK heat shrink to color code the battery wires.
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And remember that "BLACK" is not "HOT" as it is in AC circuits.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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