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#11
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PaulaJay1 wrote:
: I have a voltmeter plugin in the cig lighter socket. It reads about 11.5 when : I trun on the master. Reads about 12.8 after engine start and after an hour : flight has worked up to maybe 13.7 or so. I plan on taking a known accurate : meter out Sat to check these reading. : My A&P says maybe the alternator needs rebuilt (at about $250). He says that : the voltage reg is solid state and either works or not - ie no adjustment. : I've had a couple of times when the bat needed a boost, so something is wrong. : Any comments before I start throwing money at the problem. The only way for voltage to drop is if there's current in the measurement chain. There are also a number of reasons that could cause these symptoms, and having a bad alternator isn't very high on the list. Since it's difficult for most people to measure current, it's worth measuring battery voltage with a number of load conditions to narrow down the search. To reduce the number of variables, measure the voltage *AT* the battery with master off, on (no engine), on (above idle some), on (cruise RPM). Do this with and without heavy loads on (pitot heat, nav, and landing light on/off together make for a good 25-40A transient). It would also be good to measure the DC and AC output of the alternator *AT* the alternator post during these tests. Possibly even the voltage at the regulator input to the alternator. Not all those measurements would likely be completely necessary, but with all of them the problem can almost certainly be found. Possible reasons: - Bad diode(s) in alternator - Bad connection on field to alternator (it will get a bit hot) - Bad connection on output of alternator (it will get a lot hot) - Bad connection with current draw between bus and cig lighter - Bad regulator (either adjustment or replacement if fixed) - Bad alternator (unlikely, since if it's turning and the windings aren't faulted, there's nothing else to be wrong) - Bad battery (unlikely since if it's dead it won't draw enough current to keep the voltage down for a long time) Lots of reasons... not quite enough info to determine the cause. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#12
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Pretty good idea. I'd imagine the spare belt would suffer some
deterioation over time, but should be good enough to get you home from some far away place. -- Gene Seibel Hangar 131 - http://pad39a.com/gene/plane.html Because I fly, I envy no one. |
#13
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On Fri, 28 Jan 2005 10:46:10 -0600, Ross Richardson
wrote: Hmmm, My solid state regulator has an adjustment under a screw that is removed. I believe it even has arrows to show increase/decrease direction. Yep, mine too. And amazingly it adjusts the bus voltage when the screw is turned! I suspect the OP's A&P is not that familiar with aircraft electrical systems. Very common. It is also explains the 'shotgun' replacement methodology that many owners have to go through to fix their electrical systems. -Nathan |
#14
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![]() - Bad battery (unlikely since if it's dead it won't draw enough current to keep the voltage down for a long time) Don't excuse the battery too quickly, although more accurate voltage and voltage drop measurements are certainly in order. Check also that the engine/alternator is grounded with respect to the battery negative, and do it under heavy load. Check also that the regulator is adequately grounded with respect to the battery negative. Remember that the airframe isn't necessarily a good conductor. Wires are used to carry current. The airframe only might do so. From reading these and other posts, Pipers seem to have an inordinate amount of electrical problems. Is it because of the aluminum wiring on the main cables? |
#15
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#16
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well.. your original post did say "strapped up against the engine"..
is part of the preflight to make sure the zip ties have not broken or gotten brittle? BT wrote in message news:UMkKd.262$by2.128@trnddc03... On 27-Jan-2005, "BTIZ" wrote: I would think the heat from the engine would raise a havoc with the belt.. and it might smell pretty bad it gets hot The "spare" belt is positioned in a way that it is well clear of the cylinders and heads. Actually, the belt doesn't even contact the crankcase that much, and the case doesn't get particularly hot. The mechanic says his shop has been doing this for a while now with no problems. -- -Elliott Drucker |
#17
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BTIZ wrote:
well.. your original post did say "strapped up against the engine".. is part of the preflight to make sure the zip ties have not broken or gotten brittle? BT Yes, I'd be worried about carrying it in the engine compartment. Why not just carry it in baggage compartment? Matt |
#18
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Matt Whiting wrote:
BTIZ wrote: well.. your original post did say "strapped up against the engine".. is part of the preflight to make sure the zip ties have not broken or gotten brittle? BT Yes, I'd be worried about carrying it in the engine compartment. Why not just carry it in baggage compartment? Matt Because from the baggage compartment you have to stretch it over the propeller to get it on (not likely!) - or remove the propeller :-) whereas if it's already between the engine and the propeller you just put it over the engine pulley, loosen the alternator, and put it over the alternator pulley. Tyler |
#19
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nrp wrote:
: Don't excuse the battery too quickly, although more accurate voltage Actually, the battery is quite likely screwed if the charging system is broken somehow. If a flooded lead-acid battery sits dead for even a short period of time (like overnight), it can be considerably damaged. If you replace the battery without fixing the charging system (a *very* common practice, BTW), you'll only succeed in destroying a brand new battery in a short period of time. When a battery goes bad, it almost always has a weak cell. In that case, It won't absorb any current without easily floating up to the max voltage. The "time-dependent" voltage rise he mentioned isn't consistent with that. If the battery is somehow taking lots of current but not charging, the energy is going somewhere else (read: heat)... badness will ensue in this unlikely failure mode. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#20
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On Fri, 28 Jan 2005 13:07:05 GMT, "Jay Honeck"
wrote: The "spare" belt is positioned in a way that it is well clear of the cylinders and heads. Actually, the belt doesn't even contact the crankcase that much, and the case doesn't get particularly hot. The mechanic says his shop has been doing this for a while now with no problems. I, for one, think it's a fabulous idea. I wish more shops would think proactively like this. I wonder what the FAA would have to say about a non standard attachment to the engine? Although this sounds really handy, I'd bet they would require it to be removed. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
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