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Charging system failure cuts short a long X-Country
I first flew to Memphis to enter the Memphis 100 race. I did it.
Then on to Atlanta to visit family. The next day I flew to Kitty Hawk. That was uneventful other than flying over water and turbulence on approach and departure from the 15 knots gusting 25. An aerial view is he http://home.pcisys.net/~ronlee/RV6A/...wkAirSmall.jpg This is my aircraft with the memorial in the background: http://home.pcisys.net/~ronlee/RV6A/...roundSmall.jpg I thought they took off from the hill but no. It was flat terrain north of the hill. The starting point is he http://home.pcisys.net/~ronlee/RV6A/...StartSmall.jpg And the end of the first flight he http://home.pcisys.net/~ronlee/RV6A/...stEndSmall.jpg I refueled at an airport west of Kitty Hawk and planned on getting back to Atlanta right around sunset. Unfortunately, around Rayleigh the voltage went to just over 12 and the amperage went negative. I had been hearing a static like popping since leaving Kitty Hawk and someone suggested that it was arcing from the failure. I told approach that I was getting lower than the approaching cloud deck and decided to make a precautionary landing at Sanford NC (KTTA). No mechanics were around so I got a rental car and went into town for the night. The next morning I replaced the voltage regulator with no success so I removed the lower cowl and found that the battery ring terminal wire on the alternator B point was fatigued and broken. It was previously bent to make proper contact. I had a mechanic install a new ring terminal but that did not make the alternator work. Using advice from a primo mechanic at home (and not being able to find a replacement alternator), I bought a battery for my Blazer, wire, ring terminals and added the new battery in parallel with my aircraft battery. Nothing blew up so I prepared to leave. The engine started normally and to my surprise the alternator worked. It worked all the way home with four restarts. On this trip I flew below an overcast with less than 6000' between me and the ground (perhaps 1500'). I flew over a broken cloud layer. I flew in less than 100 nm visibility. As I approached Springfield MO towards sunset, I descended thinking that I was about to overfly a cloud layer. Nope. It was haze. Silly me. It made more sense to stay where I could see ground to the sides anyway. I had planned on going to Key West and the Bahamas but elected to get home to fix the alternator problem. TS Noel would have kept me from doing that anyway. In retrospect, the alternator to bus wire/ring terminal should have been made better long ago. That will be corrected. I am now in the process of trying to decide which readily available alternator I will install. The current one will not fly again. I also did not know what my safe flying time was when the ring terminal broke. Perhaps I could have flown another two hours (4-5 amp current draw and one EI) on a PC925 battery. But since I did not know for sure, I played it safe and landed at the nearest airport. With the truck battery, it may well be 20 hours. Regardless, I did buy a battery charger just in case. I did find out that the RV community is awesome. Three guys stopped by to offer assistance (I did the repairs on the ramp). The FBO at Sanford was great as was the mechanic shop. Stopping at new airports is fun. I expanded my flight experience beyond CAVU but nowhere near scud running. The haze illusions were baffling but I just reacted with safe flight adjustments. |
#2
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Charging system failure cuts short a long X-Country
Ron Lee wrote:
In retrospect, the alternator to bus wire/ring terminal should have been made better long ago. That will be corrected. I am now in the process of trying to decide which readily available alternator I will install. The current one will not fly again. Not that I wish to impose upon your own maintenance decisions or state that safe is, in fact, not better than sorry, but the alternator may well be just fine (excepting the ring terminal, of course). Alternators have to be supplied with a sufficient current from the battery in order to generate the larger currents required by the aircraft systems. This is fine as long as the alternator is functioning, because it is generating enough current to recharge the battery (and then some). Without that initial current, though, the alternator will never work, no matter how hard you spin it (a generator, on the other hand, would). It sounds as though the ring terminal broke, disconnecting the alternator, and the battery discharged sufficiently in the intervening time such that the alternator couldn't achieve a proper magnetic field. Your mechanic's suggestion to add an additional battery in parallel provided the system with the amperage it needed, and the alternator began to work again. My advice is to have the alternator tested before chucking onto yonder scrapheap. Regardless, glad to hear you and the aircraft escaped unharmed. TheSmokingGnu |
#3
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Charging system failure cuts short a long X-Country
"Ron Lee" wrote The engine started normally and to my surprise the alternator worked. It worked all the way home with four restarts. Hi Ron, Thanks for the report of your electrical problem. I always learn valuable insights from reports like this. Thanks for sharing. By the way, beautiful RV6! I'm not arguing, just curious; why replace the alternator if it performed normally on the way home? I'm no expert, but I wonder if the problem is in the control circuitry or the old, partially discharged battery. How old was the battery? The real expert on stuff like this is Bob Nuckolls at http://www.matronics.com/Navigator/?AeroElectric-List Glad it worked out, Dennis |
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Charging system failure cuts short a long X-Country
TheSmokingGnu wrote:
Alternators have to be supplied with a sufficient current from the battery in order to generate the larger currents required by the aircraft systems. This is fine as long as the alternator is functioning, because it is generating enough current to recharge the battery (and then some). Without that initial current, though, the alternator will never work, no matter how hard you spin it (a generator, on the other hand, would). This may be exactly what happened. The workings of an alternator are "magic." Since I did have a similar alternator experience where it would not start once before...and the solution was for an alternator shop to energize it by touching the "N" terminal I believe with positive voltage, I did that as well. Either it should have been the "F" or "E" terminal or I did it incorrectly. I am changing out to an internally regulated alternator that is easily obtainable. My current alternator is not either. Ron Lee |
#5
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Charging system failure cuts short a long X-Country
SockPuppet wrote: In article cc1Xi.198$Cb.81@trnddc08, anonymityisavirtue@ 1111011010011.com says... Alternators have to be supplied with a sufficient current from the battery in order to generate the larger currents required by the aircraft systems. This is a new concept to me, can you elaborate? My understanding of alternators is that mechanical energy from the engine causes the alternator to spin, which then powers aircraft components and (when regulated correctly) can recharge the battery. Is there something about aircraft alternators that requires the battery to power them (rather than the other way around)? Yes, they need a little charge in the battery to start charging themselves. Absolutely dead battery? Alternator is useless. |
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Charging system failure cuts short a long X-Country
"SockPuppet" wrote Is there something about aircraft alternators that requires the battery to power them (rather than the other way around)? Your car alternator works the same way. The only difference is that if your car engine is running (and it's not a diesel) then it has electricity in the first place, (to run the ignition, and probably a fuel pump) then there will be electricity to create the magnetic field around the alternator for it to produce more electricity. The same can not be said for an airplane. It is perfectly happy to run without any electricity, so with no electricity in the first place, there is nothing to make the magnetic field in the alternator for it to produce more electricity. That, plus the fact that most alternators in airplanes have external voltage regulators, and a switch in place as a standard device that is there to turn off the magnetic field for the alternator windings. I can't think of any cars that have that feature in place. -- Jim in NC |
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Charging system failure cuts short a long X-Country
Newps wrote:
Alternators have to be supplied with a sufficient current from the battery in order to generate the larger currents required by the aircraft systems. Is there something about aircraft alternators that requires the battery to power them (rather than the other way around)? Yes, they need a little charge in the battery to start charging themselves. Absolutely dead battery? Alternator is useless. I was able to start my engine several times easily so I doubt that battery charge was an issue. My best recollection is that the voltage was around 12.2 V. Yet adding another battery in parallel did seem to make a difference. It really is magic or I just am not well educated on the intricacies of how they work...or don't work. Ron Lee |
#8
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Charging system failure cuts short a long X-Country
SockPuppet wrote:
In article cc1Xi.198$Cb.81@trnddc08, anonymityisavirtue@ 1111011010011.com says... Alternators have to be supplied with a sufficient current from the battery in order to generate the larger currents required by the aircraft systems. This is a new concept to me, can you elaborate? My understanding of alternators is that mechanical energy from the engine causes the alternator to spin, which then powers aircraft components and (when regulated correctly) can recharge the battery. First, recall that electricity induces magnetic fields and magnetic fields induce electricity and vice versa, and vis a vis and so forth. A simple generator is a wire coil rotating in opposite poles of two permanent magnets. The magnetic field is provided by the magnet, and the faster the coil spins, the more often the magnetic field cuts through the coil (or more properly, the coil cuts through the magnet's field), the more current is generated. Alternators use a different method to generate current. There is a wire-wound stator, within which spins a drum coil (with soft iron cores). The drum coil (or rotor) has to be energized from an outside source in order to generate the magnetic fields, necessary to induce current in the stator windings. While the process is self-sustaining once begun, alternators cannot "bootstrap" themselves into current generation (since you can't generate the current to generate the fields to generate the current, so to speak). Much like the magnetos need the impulse coupling to push the engine over with a hot spark, the alternator needs the external "kick in the pants" to begin outputting current, which is the battery. Now, as I recall, we use alternators instead because they're lighter, more efficient, and higher output than can be achieved with a bog-standard generator. TheSmokingGnu |
#9
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Charging system failure cuts short a long X-Country
On Nov 5, 7:30 am, TheSmokingGnu
wrote: SockPuppet wrote: In article cc1Xi.198$Cb.81@trnddc08, anonymityisavirtue@ 1111011010011.com says... Alternators have to be supplied with a sufficient current from the battery in order to generate the larger currents required by the aircraft systems. This is a new concept to me, can you elaborate? My understanding of alternators is that mechanical energy from the engine causes the alternator to spin, which then powers aircraft components and (when regulated correctly) can recharge the battery. First, recall that electricity induces magnetic fields and magnetic fields induce electricity and vice versa, and vis a vis and so forth. A simple generator is a wire coil rotating in opposite poles of two permanent magnets. The magnetic field is provided by the magnet, and the faster the coil spins, the more often the magnetic field cuts through the coil (or more properly, the coil cuts through the magnet's field), the more current is generated. Alternators use a different method to generate current. There is a wire-wound stator, within which spins a drum coil (with soft iron cores). The drum coil (or rotor) has to be energized from an outside source in order to generate the magnetic fields, necessary to induce current in the stator windings. While the process is self-sustaining once begun, alternators cannot "bootstrap" themselves into current generation (since you can't generate the current to generate the fields to generate the current, so to speak). Much like the magnetos need the impulse coupling to push the engine over with a hot spark, the alternator needs the external "kick in the pants" to begin outputting current, which is the battery. Now, as I recall, we use alternators instead because they're lighter, more efficient, and higher output than can be achieved with a bog-standard generator. TheSmokingGnu The alternator has diodes in it, and those cause a slight voltage drop in the output process. If the battery is too weak to produce a sufficiently strong magnetic field in the rotor to generate sufficient voltage in the stator to overcome diode resistance, bootstrapping cannot occur. The old generators had no diodes, and residual magnetism in the field pole shoes would start the thing generating. There's a bit of residual magnetism in the alternator's stator but not enough to do any good with those diodes in the way. Alternators in aircraft should be taken off, opened up and inspected every 500 hours. The brushes wear and if they get short they'll fall out of the holder and their springs will gouge up the slip rings. Gets a lot more expensive than the 500 hour check. Airplanes that don't fly much have alternator bearings in which the grease dries out, and bearing failures happen. Regulators, especially the newer electronic replacements for the electromechanical-switch types, give us plenty of grief. Regulators fail more often than alternators. And as the OP found, those dumb crimp terminals breal through vibration fatigue. Alternator output breakers age, their contacts corrode and cause resistance heating and they start popping off,causing the naive mechanic to spend lots of time looking for a short. Dan |
#10
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Charging system failure cuts short a long X-Country
"Ron Lee" wrote I was able to start my engine several times easily so I doubt that battery charge was an issue. My best recollection is that the voltage was around 12.2 V. Yet adding another battery in parallel did seem to make a difference. It really is magic or I just am not well educated on the intricacies of how they work...or don't work. Could be that after starting it several times, there was voltage available, but that it could not push enough amps to excite the alternator field. Could also be that the voltage regulator has the ability to see very low voltage, and not use any of the remaining electricity to excite the alternator field. -- Jim in NC |
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